US20110060738A1 - Media item clustering based on similarity data - Google Patents

Abstract

Methods and arrangements for facilitating generation of media mixes for a program participant based at least in part on media library inventory information provided by a number of program participants. Those individuals that decide to be program participants are interested in organizing, maintaining and playing their music, based at least in part, on data derived from a population of other participants in the program. A program participant must send, and the system, receive, data representative of that program participant's media inventory. The system or program determines a relative similarity of each item from the collection of program participants as compared to each other item and from the similarity information clusters of similar items are identified. The clusters can be used to identify clusters of similar items in an individual program participant's media library and therefrom mixes of similar media items can be created.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• This application claims the benefit of U.S. Provisional Patent Application No. 61/240,630, entitled “MEDIA ITEM CLUSTERING BASED ON SIMILARITY DATA”, filed on Sep. 8, 2009, and which is hereby expressly incorporated herein by reference in its entirety.
BACKGROUND
• 1. Technical Field
• The present disclosure relates to clusters of media items and more specifically to generating media mixes based on clusters of media items.
• 2. Introduction
• Before the age of compressed media files such as MPEG, ACC, WMA media was stored on magnetic tapes and later compact discs (CDs). Especially with reference to music media files, consumers typically bought music media as albums comprising several music tracks. Frequently these albums contained tracks which a listener would associate with varying degrees of enjoyment, either because of the suitability of the individual track to the listener's tastes or the listener's present listening mood.
• This frequently led to the situation where the tracks a listener would like to listen to were scattered over several or even many albums. Motivated by this situation, user's commonly created “mixes” of their favorite audio tracks or “mixes” of audio tracks that were similar and therefore sounded great when played together on the same tape or compact disc.
• To create these mixes, users had to have great knowledge of all of the tracks in their collection. Further users had to record each track from its original media onto another media. Often user's spent hours listening to tracks to determine which tracks could fit on the limited space of a tape or CD and to determine the order.
• Today many media consumers buy individual tracks rather than buy complete albums. Also users today often listen to a greater number of tracks in their library since their entire collection can fit on one device instead of many tapes or CDs.
• Despite this relative convenience of having access to every track in their media library at any time and being able to access each track with a scroll and a click, listener's still create mixes of tracks, often in the form of playlists. However, creating these mixes is still time consuming processes requiring a great deal of user interaction and many user decisions. Accordingly there is a need to eliminate the burden on the listener while still creating high quality mixes.
SUMMARY
• Additional features and advantages of the concepts disclosed herein are set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the described technologies. The features and advantages of the concepts may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the described technologies will become more fully apparent from the following description and appended claims, or may be learned by the practice of the disclosed concepts as set forth herein.
• The present disclosure describes methods and arrangements for identifying clusters of media items in a program participant's media library for use in creating mixes of media items. To create the highest quality mixes, the clusters are based on the input of an entire population of users.
• A population of program participants all share information about the contents of the individual media items in their music libraries with a server hosting the program in exchange for receiving clustering data related specifically to their individual music libraries.
• In some embodiments items are identified as similar based on an analysis of the program participants' libraries. For every media item represented in at least two program participants' media libraries a vector is plotted representing the presence of that media item in the respective program participants' libraries. Each vector, represents a media item and can be compared to every other vector. For any two items, the closer the relationship between any two vectors, the more similar those two items are said to be with respect to each other.
• Using the similarity data identified above, a clustering analysis can map the individual media items collected from the program participants' libraries into server clusters or groupings of media items in the server database that are all relatively similar to each other. In some embodiments, the clustering analysis can be applied recursively on each server cluster to result in smaller server clusters comprising media items having a stronger similarity relationship to each other than the media items comprising the “parent” cluster. By recursively applying the cluster analysis a tree-like relationship of server clusters can be generated with each “parent” server cluster having two or more “child” server clusters dividing the contents of the “parent” server cluster among the “child” server clusters. This recursive analysis can be applied as often as desired, but in some embodiments the analysis is reapplied until “child” server clusters have 1000 media items or less, or 100 media items or less, or 50 media items or less. Server clusters meeting this criterion will be the lowest-level server clusters in the tree.
• In some embodiments the clustering analysis is combined with editorial partitions. While it is simplest to perform the editorial partitions before the clustering analysis, the editorial partitions can be performed at any time. In some embodiments canopies of non-overlapping groups of potentially similar media items are created based on genre information before the clustering analysis is performed. For example, in the case of music, music media items that belong to the “rap” genre will never be considered similar to music media items that belong to the “opera” genre. Accordingly, the entire collection of media items can be separated into large canopies of non-overlapping groups such as “rock”, “rap”, “classical”, “opera”, etc. However, just because media items are grouped together into the same canopy, it does not mean that each of those items is similar to each other, but they can be.
• The server can generate participant clusters that contain only media items present in a program participant's media library by projecting the similarity relationships represented by the server clusters into a program participant's media library. Since the server already knows of the contents of a program participant's media library, the server can determine which lowest-level server clusters contain each item in the program participant's media library and form participant clusters therefrom.
• If any one of the participant clusters contains too few media items, for example less than 20 or less than 50 media items, the server can recursively agglomerate clusters sharing a common parent server cluster. By repeating the agglomeration action, a program participant's media items that descend from a common parent are accumulated into a larger participant cluster until the participant cluster has reached an acceptable size. In some embodiments the agglomeration action continues until only a determined number of clusters remain.
• The server can send, and a client device can receive, information about participant clusters created from the media items of a program participant's media library. The client device can receive a listing of all media items contained in any given cluster from the server. As described above, the clusters have been compiled based on an agglomeration of the program participant's tracks found in hierarchically related participant clusters of media items on the server. The clusters of media items have been determined based on a cluster analysis of the media items in the server's inventory based on the relative similarity of each song in the inventory to each other, the relative similarity among songs have been determined by an analysis of the incidences of co-occurrence of media items within different program participants' media libraries.
• The resulting participant clusters can be used to generate and play a mix of media items. The mix comprises media items represented in one of the clusters of media items contained within the program participant's collection of media items received from the server. In some embodiments, the mix contains a selection of some of the items represented in a cluster and other songs deemed similar to those media items. In other words, the media items of the cluster can act as seed items for the rest of the mix. It will be appreciated that there are numerous ways to select which media items from within the cluster will be used as seed items to create the mix. For example in some embodiments, the media items can be selected based on their relative similarity to the cluster as a whole. In some embodiments, all the items of the cluster can be used in creating the mix.
• It should be appreciated that unique aspects of this overall program or system take place on servers of the media supplier (online music store), the media playing devices of the participants, and often intermediate facilities, such as the users' personal computer that accommodates communication between the playing device and online store's computer systems.
BRIEF DESCRIPTION OF THE DRAWINGS
• In order to best describe the manner in which the above described embodiments are implemented, as well as define other advantages and features of the disclosure, a more particular description is provided below and is illustrated in the appended drawings. Understanding that these drawings depict only exemplary embodiments of the invention and are not therefore to be considered to be limiting in scope, the examples will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:
• FIG. 1 illustrates an example system embodiment;
• FIG. 2 illustrates an example method embodiment for receiving and identifying items in a program participants library and generating similarity data;
• FIGS. 3A and 3B illustrate a method of determining correlation data;
• FIG. 4 illustrates a sample purchase matrix;
• FIG. 5 illustrates a column in a master similarity table;
• FIG. 6 illustrates an individual similarity table;
• FIG. 7 illustrates an exemplary method of identifying clusters in a vector space;
• FIG. 8 illustrates an exemplary method of identifying sub-clusters in a vector space;
• FIG. 9 illustrates an example server cluster embodiment;
• FIG. 10 illustrates an exemplary method of generating server clusters;
• FIG. 11 illustrates an exemplary method of generating server clusters;
• FIG. 12 illustrates an exemplary method of computing a cluster vector;
• FIG. 13 illustrates an example server clusters and canopies embodiment;
• FIG. 14 illustrates an exemplary method of generating participant clusters;
• FIG. 15 illustrates an exemplary method of generating participant clusters;
• FIG. 16 illustrates an example system embodiment;
• FIG. 17 illustrates an exemplary method of receiving similarity data;
• FIG. 18 illustrate an example playlist method embodiment;
• FIG. 19 illustrates an example media mix method embodiment;
• FIG. 20 illustrates an exemplary method embodiment for recommending items for purchase;
• FIG. 21 illustrates an example system embodiment; and
• FIG. 22 illustrates an example system for synching media and similarity tables to a digital media player.
DETAILED DESCRIPTION
• Various embodiments of the disclosed methods and arrangements are discussed in detail below. While specific implementations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components, configurations, and steps may be used without parting from the spirit and scope of the disclosure.
• With reference toFIG. 1, an exemplary system includes a general-purpose computing device100, including a processing unit (CPU)120 and asystem bus110 that couples various system components including the system memory such as read only memory (ROM)140 and random access memory (RAM)150 to theprocessing unit120.Other system memory130 may be available for use as well. It can be appreciated that the system may operate on a computing device with more than oneCPU120 or on a group or cluster of computing devices networked together to provide greater processing capability. Thesystem bus110 may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. A basic input/output (BIOS) stored inROM140 or the like, may provide the basic routine that helps to transfer information between elements within thecomputing device100, such as during start-up. Thecomputing device100 further includes storage devices such as ahard disk drive160, a magnetic disk drive, an optical disk drive, tape drive or the like. Thestorage device160 is connected to thesystem bus110 by a drive interface. The drives and the associated computer readable media provide nonvolatile storage of computer readable instructions, data structures, program modules and other data for thecomputing device100. In one aspect, a hardware module that performs a particular function includes the software component stored in a tangible computer-readable medium in connection with the necessary hardware components, such as the CPU, bus, display, and so forth, to carry out the function. The basic components are known to those of skill in the art and appropriate variations are contemplated depending on the type of device, such as whether the device is a small, handheld computing device, a desktop computer, or a large computer server.
• Although the exemplary environment described herein employs a hard disk, it should be appreciated by those skilled in the art that other types of computer readable media which can store data that is accessible by a computer, such as magnetic cassettes, flash memory cards, digital versatile disks, cartridges, random access memories (RAMs), or read only memory (ROM), may also be used in the exemplary operating environment.
• To enable user interaction with thecomputing device100, aninput device190 represents any number of input mechanisms, such as a microphone for speech, a touch-sensitive screen for gesture or graphical input, keyboard, mouse, motion input, speech and so forth. Thedevice output170 can also be one or more of a number of output mechanisms known to those of skill in the art. In some instances, multimodal systems enable a user to provide multiple types of input to communicate with thecomputing device100. Thecommunications interface180 generally governs and manages the user input and system output. There is no restriction on the disclosed methods and devices operating on any particular hardware arrangement and therefore the basic features may easily be substituted for improved hardware or firmware arrangements as they are developed.
• For clarity of explanation, the illustrative system embodiment is presented as comprising individual functional blocks (including functional blocks labeled as a “processor”). The functions these blocks represent may be provided through the use of either shared or dedicated hardware, including, but not limited to, hardware capable of executing software. For example the functions of one or more processors presented inFIG. 1 may be provided by a single shared processor or multiple processors. (Use of the term “processor” should not be construed to refer exclusively to hardware capable of executing software.) Illustrative embodiments may comprise microprocessor and/or digital signal processor (DSP) hardware, read-only memory (ROM) for storing software performing the operations discussed below, and random access memory (RAM) for storing results. Very large scale integration (VLSI) hardware embodiments, as well as custom VLSI circuitry in combination with a general purpose DSP circuit, may also be provided.
• The logical operations of the various embodiments are implemented as: (1) a sequence of computer implemented steps, operations, or procedures running on a programmable circuit within a general use computer, (2) a sequence of computer implemented steps, operations, or procedures running on a specific-use programmable circuit; and/or (3) interconnected machine modules or program engines within the programmable circuits.
• The computing device described above is particularly useful for generating and using mixes of media items based on a clustering analysis of similarity data derived from a large sample of users. Based on mathematical analysis to determine the incidence of correlation of two or more songs across multiple users' libraries, a statistical similarity can be determined. From the statistical similarity data, a clustering analysis can divide a large data set into smaller sets of related media items. By projecting the results of the analysis of the large data set into smaller data sets (media libraries of individual program participant's) high quality mixes of media items can be created.
• This similarity data can be used for a variety of helpful functions including generating high quality playlists, determining suggested products for recommendation to a user for purchase, keeping a user's media device up-to-date with a fresh selection of songs, generating mixes from a user's media library among others. In one example, users may upload information relating to the contents of their entire media database to a server accessible to a wide audience of users. Based on how often two or more media items co-occur in the libraries of the entire audience of users, media items become correlated to each other and are noted as similar. Based on this similarity, the server can create a playlist to include one or more similar songs based on the selection of a seed track, or the server could recommend purchase of similar songs not in the user's library. These and other features of the system will be described in more detail below.
• The clusters can be used in any way in which a collection of similar items can be used. In one example, clusters are useful in generating playlists based on the contents of a cluster. In another example, clusters are useful in generating mixes of media items. Mixes in this context are analogous to the concept of music mixes wherein a listener would create a CD or tape of a selection of music items that went well together. In this case, clusters provide the device with a method of automatically generating mixes of media items.
• While many of the features of the described techniques and products will be described with reference to an online music store such as Apple Inc.'s ITUNES Store, it should be appreciated that the system does not require any media sales whatsoever to carry out the preferred embodiments of the system. Further, while some of the descriptions may refer only to one particular form of media, the principles described herein can be applied to any media, such as audio, video, still pictures, documents and other types of data files.
ServerUploading
• FIG. 2 illustrates an example method embodiment for generating similarity data. The method includes receiving by a server, user data related to program participants' personal media inventory (202). The user data comprises identifying information regarding individual media items in a user's library usually in the form of metadata. The origin of the media items within a user's library is not relevant to the system. Even if the method described is employed by a music content store, the present embodiment does not require that a user's files originate from the music store since the server does not differentiate between file information based on source—all media items are treated the same. The method applies equally to physical media, such as CDs, DVDs, or HD-DVDs, as well as instances where the physical media is transcoded to digital format and entered into the user's media library. In a preferred embodiment, the server does not require that a user upload information regarding all media items in their library; information regarding only a limited number of media items or only partial information about the media items is also accepted by the server.
Identifying User Data
• The method also includes identifying the user data as specific media items (203). This step may be accomplished in any one of a number of ways including examining the file name, metadata or through a detailed analysis of a portion of the file. In the example of a music track, the server can identify the music track through a variety of mechanisms. For example, a given track such as Led Zepplin's Stairway to Heaven having a length of approximately eight minutes can have a variety of data associated with the file including the file name or metadata identifying the artist, song name, genre, length of track, album name, track number, etc. A portion of this data can be sufficient for the server to identify the file as Led Zepplin's Stairway to Heaven from the album Led Zepplin IV. Alternatively, commercial song identification services can be used to identify the file. It is also possible to identify the track by sampling a portion of the music track or by recognizing a unique identifier from a purchasing store or by recognizing the songs digital fingerprint. For example, the server or service can recognize that a song was bought from the ITUNES Store and the file's metadata contains a unique identifier specific to the ITUNES Store. The server can identify the media item by that identifier. It should be appreciated that many other possible methods of recognizing media items are well known and all of which are encompassed by the disclosed method and arrangement.
Correlation
• Each media item is associated with a unique identifier (204) and stored in a table (205). If the server has never encountered the song before, the server assigns a new identifier to that track. However, for most media items, an identifier will already be assigned and media need only be correlated with that identifier. Continuing with the example of Stairway to Heaven, once the media item has been identified as that track, the server can look up the unique identification data for that track. This process is repeated for each media item received by the server.
• Although the server will already have an identifier to associate with most songs, in some cases, the media item will be completely new to the server, or at least recognized as such. In these cases, the server will issue a new identifier and assign it to that media item. For example, a new artist or garage band might not be recognized by the server. However, the server will issue a new identifier for that artist's track and when the server encounters the same track in a different user's library, it will assign the same identifier to that track as was previously issued.
• In some cases, the server might not supply a new identifier to a media item that is new to the server. For example, a media item might be unique to a user's library and therefore providing an identifier would not be of any value since there would be no incidences of co-occurrence for that item. Accordingly, the system need not supply a unique identifier to all new items. Later, the system can supply a unique identifier for that track and supply similarity data for that item if and when other users also have that media item in their libraries.
Master Purchase Matrix
• Each media item is stored in a master purchase matrix instep205. An illustration of the master purchase matrix is shown inFIG. 4. Thepurchase matrix402 is a table that containscolumns404 corresponding to each unique media item in the table. In the embodiment wherein the table is hosted by a music content seller, such as the ITUNES Store, the purchase matrix will also include all media items available for purchase from the ITUNES Store. The rows of themaster purchase matrix404 are associated with user unique user identification numbers406. This identification code represents users by an anonymous identification code possibly known to the user, but not the system. Thus the master purchase matrix contains a record of every file received by the program server from every user that participates.
• As the purchase matrix accommodates all program participants and all media in each program participant's library, thepurchase matrix402 is likely to be staggeringly large. For example, if a music store has approximately 2.25 million users and more than 5 million songs, a purchase matrix for such an online store would be a table of approximately 2.25 million rows and 5 million columns, or 1,125 billion individual cells. ITUNES Store has over 50 million registered users and contains over 10 million songs. A purchase matrix for such an online store could be a table of approximately 50 million rows and 10 million columns, or 500,000 billion individual cells.
• For songs in a user's library, the cell in the matrix corresponding to that user and that song is marked. The marking may be done with a data type as simple as a Boolean, 1 for purchased408 and 0 for not purchased410. Other data types may be used when more data must be stored than a Boolean data type will allow. While the matrix can be very large, it is very sparsely populated because most users have relatively few songs (compared to 5 million) in their library. Each user row may only contain a handful of entries while each song column may contain tens, hundreds, thousands, or even millions of entries for more popular songs, but the vast majority of the purchase matrix is empty.
• It should also be appreciated that the master purchase matrix or table will require updating as user libraries change, from adding new songs to their library, changing file metadata, or deleting files. The purchase matrix may be updated in real time or transactions may be queued up for insertion at a later date. One arrangement for queuing inserts transactions into the purchase matrix on a regular basis, such as every day at 11:30 p.m. Another queuing arrangement inserts transactions into the purchase matrix when some minimum number of transactions is ready for insertion.
• Updates to the purchase table do not requirerepeating steps203 and204 for all media items. Media items that have already been identified and correlated to a program-based identification number do not require the identification and correlation step because it has already been performed when the user's data initially populated the table. In one embodiment, once the server has correlated the media item to its identification data, the server can send the identification data back to the user for storage in metadata. In future communications with the server, the server can receive updates to a media item with the associated identification data thus avoiding the need to redostep204.
• In some embodiments the purchase matrix may be part of a larger table or matrix including additional information regarding each transaction such as time and date of sale, what format the media is in, whether the media is high definition or standard definition, whether the transaction is a gift or whether it was paid for, which devices are authorized for playback, etc. The purchase matrix may be discrete, separate tables or may be wholly integrated into a larger table or matrix.
• In still yet another embodiment, the master purchase matrix need not contain uploaded information about a user's media inventory. The master purchase matrix can be essentially comprised of purchase information. Purchase information can be only items purchased from the online store by users or can include additional information. In this embodiment the table can contain a list of all items purchased by each user. Still, the master purchase matrix would likely contain at least a limited set of data regarding the content of a user's media inventory.
Collabarative Filter Engine
• The method illustrated inFIG. 2 next comprises running a calibration filter engine (shown as308 inFIG. 14) on the master purchase matrix to generate similarity data (206) and store the similarity data in a master similarity table (207). Similarity data can be derived from a media item's incidence of co-occurrence with some other media item in the master table. When users have the same two media items, they are said to co-occur. Such co-occurrence in multiple users' libraries is an indication that the two media items are “similar.” The more often two media items co-occur in program participants' libraries, the more similar the media items are said to be.
• Thecollaborative filter engine308 calculates the similarity between individual media items in the master purchase table. In one embodiment the collaborative filter engine can be as simple as a program that tallies the number of times pairs of songs in the database co-occur in the program participants' libraries.
• In some embodiments, the collaborative filter engine can calculate the similarity between two different media items by representing each item as a vector in a multidimensional vector space. The number of dimensions is equal to the number of users in the purchase matrix306 (inFIG. 14). A correlation between items is developed by computing the distance between the vectors. A pure or modified trigonometric function (e.g. cosine or sine function) can be used to calculate the distance between vectors. If the two vectors have a small angle, they are considered to be similar and if the two vectors have a large angle, they are considered to be less similar. This process is carried out by comparing each song in the master purchase matrix to every other song in the master purchase matrix.
• In some embodiments the collaborative filter engine can take into account more than the incidence of co-occurrence data. For instance, the incidence of overall occurrence can be factored into the similarity rating. For example, songs A and B may co-occur equally as often as songs A and C, but songs A and B can have a higher similarity score (that is, deemed more similar) than songs A and C if song B is more popular overall. One way of determining the popularity of the different songs is by measuring how often each song occurs in the overall data set.
• Likewise there can be other inputs into the collaborative filter engine which affect similarity scores, such as usage inputs. For example, ratings given to the media items, play counts, and skip counts can all be inputs into the collaborative filter engine for determining similarity between media items.
• FIGS. 3A and 3B illustrate the concept of representing each song as a vector. InFIG. 3A, a vector for Media ID629 in the master table has been mapped out based on the songs existence in the libraries ofusers 2, 899, 1,343 and 2,000 Likewise, a vector has been mapped forMedia ID1,263,999 in the master table based on the song's existence in the libraries ofusers 2, 12, 444, 1,343. The angle between these two vectors is measured to be twenty degrees and calculates to a cosine value of approximately 0.939. The cosine value represents the correlation value between Media ID629 andMedia ID1,263,999.FIG. 3B represents another correlation calculation to determine the correlation between Media ID629 andMedia ID15. In this example only one user has both Media ID629 andMedia ID15 in their libraries and therefore the cosine value between these two vectors is approximately 0.707. The lower score indicates thatMedia IDs629 and15 are not closely correlated to each other.
• In another embodiment, other functions can be used to calculate the similarity scores between items. By way of example the similarity score can be calculated in a method that takes into account the percentage of an item's total co-occurrences that is made up by a particular item. For example item A co-occurs with items1-5 and the item A's total co-occurrences is the sum of all the co-occurrences with items1-5. For instance, if item A co-occurs withitem1 two times,item2 two times,item3 two times,item4 ten times, anditem5 two times, then item A has 18 total co-occurrences. It can be valuable to learn what percentage of the total number of co-occurrences is due to a particular pair. For example,item 4 represents approximately 55% of all of item A's co-occurrences and therefore is more strongly correlated with item A than any of the other items which represent only about 11% each of the total of A's co-occurrences. This data can also be used to determine similarity data. Although two specific methods of calculating similarity data are illustrated above, it will be appreciated that any number of other methods of calculating the similarity between two items can be used.
• The process above is computed between every item and every other item at some regular interval. As this process could take inordinate amounts of time, it is typically performed offline. It could be performed once a month, once a week, once a day, or as frequently as computing capability allows.
Similarity Table
• The correlation data compiled by the collaborative filter engine is used to generate a master similarity table (207 ofFIG. 2).FIG. 5 illustrates data stored in a master similarity table502. For a given media item, there is an entry in the master similarity table identifying the media item by its program-basedidentification data504. Each other media item considered to be similar or correlated to that media item is also listed in the table508. In this way the table502 maintains a list of all media that is similar to each media item in themaster purchase matrix402.
• Items are included in the master similarity table if they have a sufficient score to be considered similar or correlated to the media item. For any given item, most of the other items are not similar at all. When the similarity score is sufficiently low, it is not included in the similarity table. The threshold for determining if a similarity score is sufficiently low or high may be dynamic or static. For example, if a similarity score ranges from −1 to 1, −1 being completely dissimilar and 1 being extremely similar, the threshold may be statically set to 0.5. The threshold may be dynamically set based on the number of occurrences of the song in the master purchase table, such as a threshold of 0.9 for songs occurring under 100 times, 0.7 for songs occurring under 5,000 times, 0.6 for songs occurring under 25,000 times, and 0.5 for songs occurring 25,000 times or more. The threshold may also be based on available storage or any other parameter.
• In other words, the master similarity table502 may incorporate all or some of the similarity scores. If the master similarity table must be constrained to fit a certain storage size, then only the best or strongest similarities are included and the rest are culled out. Similarly, if not enough program participants have an item in their media inventory, it could be excluded. One variation on this is to require a minimum number of occurrences in users' libraries before an item is eligible for inclusion into the master similarity table. For example, if two items have a co-occurrence of five or less, i.e. if five or less people have both of these items, the system does not compute the rest of the score.
• In some embodiments the master similarity table can also store equivalency relationships. For example,media ID17 in table502 may correspond to “O Sole Mio” by Luciano Pavarotti, as performed in 1990. Multiple renditions of “O Sole Mio” by artists such as Enrico Caruso and Mario Lanza are available in the online store and are consideredequivalent media506. Other notable types of equivalent media include official album tracks, unplugged acoustic tracks, live concert tracks, cover tracks by other bands, and even foreign language tracks of the same song. A single song may exist in all the listed forms, and more. The determination of equivalency can be performed by hand or can be automatically performed based on the actual media content, metadata, and/or other available data. Equivalent media IDs for each are presented alongside themedia ID504 to identify that each of them is considered the same and that they are counted together.
• The IDs in the master similarity table may be the same as those used in thepurchase matrix306 to index media or they may be based on an entirely different scheme. If the two do not align, a translator function or reference translation table can be provided to convert one ID to the other and vice versa. A common ID space shared between the two is likely to be the easiest and simplest to maintain without a performance penalty.
User Similarity Tables
• Although the master similarity table contains the universe of similar media, a personal media library is almost certain to include a lesser subset of that universe of similar media. Thus, a constrained set, or an individual similarity table, is generated. The constraint is tailored to media availability in a given library. The constrained set may also include references to similar media not found in the media library. This can be done in order to target suggested media purchases to a user. Such targeted suggested purchases are likely to be more appealing to the user because other people with some common media tastes already have the suggested purchase in their library.
• Once the master similarity table502 is calculated and populated, individual similarity tables602 are generated.FIG. 6 illustrates an individual similarity table. An individual similarity table602 contains amedia ID604 for each song contained in the individual's media library and media correlated to that media ID. Correlatedmedia606 are shown in braces. Correlated media in an individual similarity table are a subset of the entire list of sortedsimilar items508 located in the master similarity table of items. The subset is selected based on which media are present in the individual's media library. In other words, for each song in the individual's library, a list of similar media also contained in the individual's library is generated.Items608 represent an alternate embodiment wherein the values are media IDs of songs that are not in the program participant's library, but are recommended for purchase.
• Individual similarity tables can be generated by the server at the server and downloaded by client devices or individual similarity tables can be created by the client by downloading only similarity data for items in the user's media inventory. Regardless of where the similarity tables are created, the process is the same. Media items are looked up in the master similarity table by that item's program-based similarity identification data. Next the system can lookup the location of the similarity data for that media item in an index. Based on the results of the lookup operations, the system can retrieve the similar items. These items are further compared with those media items in a user's media library and only those items that are present in the user's media library are stored in the individual similarity table. In an additional embodiment, some highly similar tracks could also be recorded in the individual similarity table to be used for suggesting purchases to the user.
• In some embodiments, at least one individual similarity table per library can be generated by the server. The client can send the library data to the server, which can identify the items in the library and generate the individual similarity table for that library by extracting the similarity data from the master similarity table pertaining to the items in that library. The resulting individual similarity table can then be downloaded to the client for use in generating playlists. The same individual similarity table can also be used by the client to create individual similarity tables for peripheral devices.
• Using these individual similarity tables, users can benefit from data derived from the entire population of users. Users can use the similarity data to create playlists, receive suggestions for new media purchases, and a variety of other possibilities.
User Data Influencing Collaborative Filtering
• In the embodiments wherein a playlist is generated based on similarity data, users can provide, or the system can require, feedback by skipping songs that they do not want to hear in that playlist or they can give positive ratings to media items that they enjoy hearing in the playlist. Such data can be uploaded from the client devices and received by the server. Feedback data can be stored in any number of different modes such as in the master purchasing index or in separate tables. Feedback can also be derived from online music stores such as the ITUNES Store. In this embodiment, user activity on the online store304 (inFIG. 14) generates feedback data. User activity on the online store can include: purchasing media items, previewing media items, searching for a particular media item title, searching for a particular media item artist or searching for a particular media item genre. Feedback data can be used by the collaborative filter engine to modify correlation scores between items.
• Feedback data from the population could potentially eliminate a correlation that otherwise exists. For example, the song Mrs. Robinson by Simon and Garfunkel may receive a strong correlation to the same song by the Lemonheads or Frank Sinatra, but users intending to generate a playlist based on the Simon and Garfunkel version might not like the different versions—perhaps due to the different genres of the cover songs. Over time, feedback data such as skipping the song or removing the item from the playlist could be used to eliminate one or both cover versions from the list of correlated items.
• In some embodiments, user feedback can also be used to modify similarity data directly on the client device without sending the feedback to the server first for use by the collaborative filter engine. In these embodiments, user feedback data can directly effect the relationships stored in the individual similarity table on the client device without first synching with the server. Alternatively, the similarity table can remain the same, but constraints can be generated based on user feedback data. For example, if a user skips a similar item often, the client itself can either no longer consider that item as similar by removing the item from the individual similarity table or can prevent the addition of the frequently skipped item from inclusion in the playlist by other means, such as a constraint in the playlist algorithm.
Updating Similiarity Table
• Over time, new media items can be added to the online store, and by extension, the master purchase table, as artists create new music and new artists emerge. Accordingly, a correlation between existing items in theonline store304 and newly added items in the online store may form. For example, if a user has Song A in his/her media library and subsequently purchases a newly added Song B that was recently introduced on theonline store304, then a new correlation between Song A and newly added Song B may form. When a user purchases newly added Song B, the transaction is recorded in thepurchase matrix306 and an updatedpurchase matrix306 is generated. Alternatively, Song B may have been added to a user's library by copying the track from a CD. In such a circumstance, the result would be the same. As long as both Song A and Song B are in the user's media library, this co-occurrence is recorded in the updated master purchase matrix.
• Thecollaborative filter engine308 uses information from the updatedpurchase matrix306 to generate an updated master similarity table ofitems316 as described above. Thereafter an updated individual similarity table322 can be generated for each user by extracting only those items in the updated master similarity table316 which have been changed. Alternatively, an entirely new individual similarity table can be created based on the new data.
Clusters
• The similarity data discussed above can also be utilized in a clustering analysis to identify groups of media items. At a conceptual level, the clustering analysis graphs items based on the similarity vectors and selects items that are plotted relatively closely together in the graph. For example,FIG. 7 illustrates a graph of several media items420-428 as similarity vectors representing media items and every media item similar to that item, wherein the vectors are grouped together to form three clusters of similarity vectors. A cluster analysisgroups media item420 in itsown cluster430, media items421-426 incluster432 and media items427-428 incluster434.
• In a music context, theclusters430,432, and434 could represent media items belonging to separate genres, sub-genres, or just groups of media items that are more related to each other than other media items.
• FIG. 8 illustrates child clusters ofcluster432.FIG. 8 shows the same similarity vector space as illustrated inFIG. 7, however, media items421-426, which were grouped intocluster432 inFIG. 7, are subdivided intochild clusters435,436, and437. Child clusters435-437 can be generated by reapplying the cluster analysis on the smaller group of items contained incluster432.
• FIG. 9 illustrates the clusters computed inFIGS. 7-8 in a tree diagram. At the top level, CLUSTER0, contains all of the media items represented inFIGS. 7-8. The secondlevel having clusters432,430,434 correspond to the same clusters inFIG. 7. The child clusters at the bottom of the diagram435,436,437 correspond to the same clusters inFIG. 8. More specifically, performing a clustering analysis on CLUSTER0 arrives at the clusters shown inFIG. 7 and illustrated by the middle nodes inFIG. 9. Likewise, performing a cluster analysis onparent cluster432 results inchild clusters435,436,437 shown inFIGS. 8 and 9.
• There are many known mathematical forms of clustering analysis. In the present technology mechanisms of hierarchical clustering are employed. Hierarchical clustering creates a hierarchy of clusters that may be represented in a tree structure, as discussed above. These algorithms can be either agglomerative (“bottom-up”) or divisive (“top-down”). Agglomerative algorithms begin with each element as a separate cluster and merge them into successively larger clusters. Divisive algorithms begin with the whole set and proceed to divide it into successively smaller clusters. A divisive clustering analysis was illustrated inFIGS. 7-9. It will be appreciated that many techniques for clustering analysis exist and can be applied in the present technology.
• In some embodiments the type of clustering analysis applied is art as a k-means analysis. The k-means algorithm assigns each point to the cluster whose center is nearest. The center is the average of all the points in the cluster—that is, its coordinates are the arithmetic mean for each dimension separately over all the points in the cluster. For example: if the data set has three dimensions and the cluster has two points: X=(x1, x2, x3) and Y=(y1, y2, y3). Then the center Z becomes Z=(z1, z2, z3), where z1=(x1+y1)/2 and z2=(x2+y2)/2 and z3=(x3+y3)/2.
• A k-means analysis performs the following steps: (1) Choose the number of clusters, k; (2) Randomly generate k clusters and determine the cluster centers, or directly generate k random points as cluster centers; (3) Assign each point to the nearest cluster center; (4) Re-compute the new cluster centers; (5) Repeat the two previous steps until the lowest level clusters have less than a determined number of media items within each lowest-level cluster. An example implementation of a K-means analysis is illustrated inFIGS. 10-12.
• In some embodiments, the database of media items is divided into canopies (102) based on any reasonable criteria. While not necessary to achieve clusters of highly similar media items, this step can be useful in a variety of ways. First, in the case of large datasets, a simple division of the database can reduce the computation resources required to compute clusters for the top level of the database. Instead of performing a statistical clustering analysis on the entire database of millions or billions of media items, the statistical clustering analysis can be performed on smaller subsets of the whole.
• Additionally, dividing the database into canopies can also enhance the quality of the resulting clusters. For example, the canopies can be generated based on editorial divisions. InFIG. 13,canopies450,451, and453 are examples of divisions of an entire database of music items into non-overlapping groupings of non-similar genres of music media items. In such instances, the editorial decision that varieties ofrock450,rap451 andopera453 music media items are never similar to each other has been made and the database of media items has initially been split into these canopies.
• In some embodiments the canopies can be divided into sub-canopies based on editorial decisions. However, in preferred embodiments, the canopies should only be divided so that the canopies or sub-canopies separate items that should never be grouped together because items in two different canopies cannot later be grouped in the same cluster.
• Next, the chosen clustering algorithm can be performed on each canopy/sub-canopy to further subdivide the database into clusters. As illustrated inFIG. 13, therock canopy450 has been divided into two sub-groupings of similar media items, pop/alt/classic rock454, and hard/metal rock455. Likewise therap canopy451 has been further divided intoeast coast rap459 andwest coast rap460 clusters. It should be noted that whileFIG. 13 illustrates the clusters being sub-divided by genre and sub-genre, this is for purposes of illustration only. The statistical clustering algorithm will sub-divide clusters according to the statistical analysis of similarity data, which is based on occurrences of media items in the libraries of program participants, and will likely produce clusters having media items in a variety of compatible genres.
• The clustering analysis can be performed as follows: The items in a given canopy or sub-canopy are randomly divided in to X (X being an arbitrary number greater than 1) number of clusters (1013). For each cluster a centroid is calculated.
• FIG. 12 illustrates one method of calculating a centroid.1050 is a collection of similarity vectors for the media items in a given cluster. The similarity vector lists media items that are the most similar to the media item in order of descending similarity. For example1050 illustrates a vector foritems1,2 and25 which are grouped in a cluster.Item1 hasmedia item1 as most similar to it anditem25 as second most similar and so on. Each item in the cluster is then given a value based on how similar the item is to the other items in the cluster. This is accomplished by assigning weighted values (weighting more similar items greater than less similar items) to each item and adding up the values. For example,1052 illustrates a table having each item found in the similarity vectors of the media items presented in the cluster and their associated weighted values. Notice that not every media item in the table is actually in the cluster.
• Item1 was most similar toItem1 and thus is given a value of 100 anditem25 was second most similar and is given a value of 99. The scores for each item are totaled to result in each item's score. For thiscluster Item1 receives a score of 199.Item25 is highly ranked in each list and accordingly receives a higher score of 298. The scoring is calculated for each item. The final scores can be sorted and used to create a similarity vector for theentire cluster1054. This process is repeated for each of the X number of clusters to result in X centroids.
• Many different scoring mechanisms are conceivable and are considered within the present technology. The illustrative method described above is just one method of calculating a centroid for the given cluster. In the present example the centroid is effectively an average of all the media item's similarity vectors of those media items within the cluster.
• Once the centroids have been calculated, the randomly created clusters can be discarded. Their purpose was only to establish centroids. Next, the similairity vector for each media item within the canopy is compared to each centroid (also a vector) (1015) and each media item is assigned to the cluster containing the nearest centroid (1016) to create X clusters.
• The process is run iteratively to generate the highest quality cluster by computing the centroid for the existing cluster (1014), and then comparing each items similarity vector to each new centroid (1015) and clustering items to the nearest centroid (1016). The process ends (1026) once either the maximum number of iterations has been completed (1022) or media items no longer migrate from one cluster to another (1024). In this way, the iterative process slowly refines the cluster analysis by refining the centroid and migrating songs into the appropriate cluster.
• The entire process can be re-run on any given cluster. For example, the process can be re-run on any of the X clusters created above to create sub-clusters as illustrated inFIG. 11. Anyone of the X clusters can be randomly divided into X sub-clusters (1028) (again, X can be any arbitrary number greater than 1). The centroid for each sub-cluster is calculated (1030), each media item's similarity vector is compared to the vector for each centroid (1034) and grouped into clusters (1036). A new centroid is calculated (1030), and each media item is compared to that centroid (1034) and grouped into clusters (1036). The process repeats until the max number of iterations has been completed (1046) or no media items change clusters (1048) and the process ends (1050).
• The process can continue to repeat until the population of media items has been reduced to a desired number of clusters or clusters of a desired size.
• In an alternate variation on the clustering method described above, instead of clustering the media items individually, the items can be clustered by artist. Just as described above, the media items will be divided based on editorial decisions which eliminates the possibility of non-similar songs by the same artist from being group together.
• For each artist represented in a canopy, a vector can be created in the same way the centroids are created and illustrated inFIG. 12. Each song by an artist in a canopy is grouped together and an artist vector is generated. The vector contains each song from the artist that is the canopy. Having computed vectors for each artist, the clustering algorithm can use the artist vectors in place of media items and organize the artists into clusters. The iterative clustering process is complete once the process has repeated a selected number of times or only a chosen number of artists remain in each cluster, for example 3 artists. Having completed the clustering process, the artist vectors can be returned into media items by identifying each song in the artists' vector.
• The process described above can be used to generate clusters of every media item in a database on a server. Once the entire database has been divided into a complete tree of server clusters, the tree of server clusters can be used to generate participant clusters. Participant clusters are specific to an individual user's library and contain only media items contained in the participant's media library.
• A program participant's media library can be mapped to the server clusters by finding each media item in a program participant's media library in a lowest-level server cluster in the tree and working up the tree of clusters until a participant cluster having at least a determined number of items is accumulated. This method is illustrated inFIG. 14.FIG. 15 illustrates a program participant's library mapped to a tree of server clusters labeled according to hierarchy. The tree represents the same relationship as the entire server cluster tree structure, but the clusters are shown illustrating the number of a program participant's media items that are in any one of those server clusters (clusters without any numbers within them do not contain any of the program participant's media items).
• A program participant's media items are mapped to the lowest level server clusters (470). See, for exampleFIG. 15, server cluster 1.1.1.1 contains 3 of the program participant's items. Table 1, below identifies the number of a program participant's media items in the lowest-level child clusters.

• 	TABLE 1
  		Number of Program
  		Participant's Media
  	Cluster Id	Items

  	1.1.1.1	3
  	1.1.1.2	2
  	1.1.1.3	1
  	1.1.3.1	5
  	1.1.3.2	3
  	1.1.3.3	4
  	1.1.3.4	5
  	1.2.2.1	10
  	1.2.2.2	12
  	1.3.1	1
  	1.3.2	1
  	1.4.1.1.1	5
  	1.4.1.1.2	5
  	1.4.1.1.3	5
  	1.4.3.1	2
  	1.4.3.2	1

• Returning toFIG. 14, the process determines if the cluster contains more than a determined number of items. In some embodiments the determined number of items can be 10 or greater, 20 or greater or 50 or greater. In some embodiments the size of the cluster can also be limited to a determined maximum. For the purposes of the present example the determined number of items is 20 or greater. Thus at471 the process determines that server cluster 1.1.1.1 contains less than 20 items and proceeds to472 and adds media items from other participant clusters into a common parent. Since cluster 1.1.1.1 shares a common parent with clusters 1.1.1.2 and 1.1.1.3 containing 2 and 1 of the program participant's media items respectively, these media items are merged into one larger participant cluster. Again the process checks the number of media items in the participant cluster and since only 6 items are present in the cluster the process repeats (472). This time, server clusters 1.1.1, 1.1.2 and 1.1.3 all share a common parent and by merging these clusters a participant cluster of 28 media items results. Now when the process checks for a determined number of items (473), the participant cluster exceeds 19 and the process ends474. The cluster is designated as475 inFIG. 15.
• As discussed above, this process of grouping similar items together by merging clusters higher in the tree is called agglomeration.
• FIG. 15 illustrates several other potential outcomes of the process illustrated inFIG. 14. Forexample participant cluster476 only required one iteration to have agglomerated a sufficient number of items.Cluster477 illustrates that the lowest level of the tree diagram for every branch will not necessarily be the same.Cluster477 began at a 5^thorder server cluster and merged all 5^thand 4^thorder server clusters into the same parent to result inparticipant cluster477.
• 478 illustrates a failed cluster. In order to agglomerate enough items to achieve the desired size,478 would need to encompass the top order server cluster. In such an instance, it can be concluded that these items to do exhibit sufficient similarity to be combined into a cluster. The cluster could fail because a programming decision has been made to disallow agglomeration beyond a certain level of the tree, or the cluster could fail for now having too many items.
System Overview
• FIG. 16 illustrates an example of onesuch system300 that can carry out the embodiments described above.Purchase Matrix306 stores data regarding all media items from each user's library. Thecollaborative filter engine308 uses the data in thepurchase matrix306 to determine the incidence of co-occurrence of each media item relative to each of the others. Thecollaborative filter engine308 can optionally use feedback data stored inobjects324 and326 to adjust similarity scores according to user preference across the population of program participants. The output of the collaborative filter engine is stored in the master similarity table by storing all media items that are deemed similar320 to a givenmedia item318. Thesimilar media items320 can be sorted to be presented in order from the most correlated items to the least correlated.
• Likewise, the collaborative filter engine can also process its inputs to divide the database in a tree ofserver clusters332. Alternatively, the tree ofserver clusters332 can be generated from the data output by the collaborative filter engine. Either data set is appropriate for a clustering analysis.
• Theonline management tool304 serves as the interface for theclient side302 and theserver side301. In a preferred embodiment, theonline management tool304 can be associated with an online store. In one embodiment, the online store may generatedata310 which can also be used by thecollaborative filter engine308 in generating similarity data. Regardless, theclient302 serves to both upload information regarding the media items stored on aclient302 and to download similarity data and clustering data from theserver301. Similarity data specific to the client may be downloaded through theonline management tool304 directly from the master similarity table316 to generate an individual similarity table322 on theclient device302 or the individual similarity table may be generated by theserver301 and downloaded to theclient device302. The client device can also communicate feedback data through theonline management tool304 to thecollaborative filter308 to aid in generating better similarity data.
• Similarly, theclient device302 can download clustering information from theserver301. In some embodiments, theserver301 calculates participant clusters for a program participant and sends information identifying the participant clusters and the media items belonging to theparticipant clusters330. In some embodiments, the server could send information detailing the presence of each of the program participant's media items in each server cluster and let the client agglomerate the participant clusters.
Client
• As is illustrated inFIG. 16, theclient device302 can take any one of a variety of forms.Client devices302 include devices such as portable digital audio players, portable digital video players, smartphones, desktop and laptop computers, television set top boxes, and any other device capable of playing media. Client devices can include offline portable devices which sync to theonline store304 through a desktop computer or other intermediate device, such as an IPOD digital audio player syncing through a cable connection with a desktop computer, an IPOD TOUCH digital audio player syncing wireles sly through a wireless router, or a smartphone syncing wirelessly through a cellular connection. As is apparent from the discussion above, the client device contains an inventory of a variety of media items. If the user of the client device wishes to benefit from the use of similarity data, the user accesses the service through an online interface. Alternatively, the client device can access the similarity data service through a client based application such as the ITUNES desktop application which communicates with a remote server via the Internet.
• Theonline store304 can be a single server or a cluster of servers which allow client devices to purchase digital media. The online store may also grant access to other ancillary media management features.
• FIG. 17 illustrates a method embodiment for downloading similarity data to the client. If this is the client's first time accessing thecollaborative program842, then the client must choose to participate by opting into theprogram844. The client is given a private user identification code atstep846. While the server will use this code to associate with the client's library, only the client contains additional identifying information. The server knows no personal or identifying information regarding either the client device or the user (program participant). Once the private identification code has been assigned, the client device can upload information regarding itsmedia library848. In some embodiments, a user may select which media items to share with the server.
• If the outcome ofstep842 indicates that the user is already a participant in the collaborative program, the client can log into the server using its private identification code instep850. Instep852, the server may request information from the client regarding changes to the media library or alternatively the client may share this information without first being requested. If changes to the library have occurred, the client uploads information regarding thechanges854. Changes can take the form of edited metadata, new items, deleted items, etc. Once up-to-date information regarding the client's media library has been sent to the server, the client can request new similarity and/or cluster data (collectively “participant data”) from the server instep856. Alternatively, the server may initiate the transmission of new or updated participant data.
• In some embodiments the client can skip the above steps and simply request updated results from the master similarity table without the need to identify the library. For example, the client can request an update for a particular item or list of items without identifying itself by identification number and without notifying the server of changes to the client's media library inventory.
• Similarity data and/or cluster data is downloaded instep858. Similarity data can be downloaded in the form of a table previously created by the server or the information can be downloaded and formatted into an individual similarity data table in real time. Cluster data can be downloaded as a list of clusters and media items belonging to the cluster. The data can be provided in the same or separate data structures or transmissions.
• Playlists are generated based on the individual similarity tables. The playlists can be generated at theclient side302, in theonline store304, or in thecollaborative filter engine308. Playlists can be generated based on the statistical similarity to one song or multiple songs. When a client device employs playlists based on individual similarity tables, certain songs may not be what the user expected or may not be pleasing to the user. When a user often skips a song that is put in the playlist based on statistical similarity, the system “penalizes” the song, reduces its similarity value, includes it in playlists less frequently, and can eventually discard it entirely from playlisting. This is effectuated by reporting when a user skips a song. That act is recorded on the client device and transmitted as feedback to the online store. The online store sends this feedback to the collaborative filter engine which stores it in a negative correlations table326. The negative correlations table stores negative indications of similarity. In this manner each user does not need to individually skip a song many times before it is rejected from the similarity table. The cumulative negative feedback will filter out unpopular songs for the group of users based on group behavior. As such, these playlists act as living organisms which evolve to suit the changing media tastes of the population of users.
• For example, if many users always skip a particular song in a playlist or if many users delete the song from their playlists, that information is recorded and assigned a weight to influence the generation of the master similarity table. The weight may be based on the number of negative correlations reported or on other aspects of user interaction. Conversely, positive user interactions with a particular song provide positive correlations. For example, if many users add the same song to an existing playlist or if many users turn the volume up during a particular song, those positive correlations are reported through the online interface to the server and are stored in a positive correlations table.
• In addition to interacting with the server, the client may also interact with other clients or peripheral devices. In one preferred embodiment, the client can be a personal computer which interacts with a portable music player such as an IPOD portable music player. In such an instance the client device can also prepare individual similarity tables for use on the peripheral device. Just as the server can prepare an individual similarity table for a client containing information for only those media items in the client's library, the client can prepare an individual similarity table for the peripheral device containing information for only those media items in the peripheral device's library. The client can load the individual similarity table onto the peripheral device just as it would any other data item.
Peripheral Device
• The peripheral device is meant to work with the client just as the client works with the server. For example, the peripheral device can notify the client of changes to its contents and request similarity data for those contents. In a more preferred embodiment, the peripheral device can be managed by the client just as a personal computer running the ITUNES desktop application manages an IPOD portable media device. In this embodiment, the client usually does not need to be updated with changes to the peripheral device's contents because the client already knows the changes by being the tool that effected those changes. In this embodiment the client can also keep the peripheral device's similarity table up-to-date based on the available data in the client's individual similarity table. Further, the peripheral device can communicate feedback data to the client for later transmission to the server.
• Again, cluster data can be sent to the peripheral device in a similar manner as to how the similarity data is updated. The client can send a cluster ID along with only media items present on the peripheral device.
• In some embodiments, the peripheral device can interact directly with the server as a client device itself. As more and more portable media players have capabilities for accessing the internet, the portable device could interact directly with the server to download the most up-to-date similarity data or to update the master purchase matrix. In such an embodiment the peripheral device could have all the capabilities of the client.
Generating Playlists
• As has been discussed, one use of the similarity data generated by the methods described herein would be to use similarity data to generate playlists. While generating playlists can be as simple as playing all similar items in the individual similarity table, the best results will likely be obtained through the use of a playlist generation module.FIG. 18 demonstrates a method embodiment for the generation of a playlist. Atstep802 one or more seed tracks are selected and are added to the playlist atstep804. Instep806 the similarity data for the seed track(s) is looked up in an individual similarity table and the similar tracks are added to a candidate list instep808. Candidates are a list of potential tracks to be added to the playlist. Whether a candidate is added to the playlist is determined by evaluating the candidate against a series of constraints.
• Constraints serve as limits on whether a song can be added to a playlist. In most cases the constraints will serve to enhance the quality of the playlist. One constraint may require certain spacing in the playlist. For example, two songs by Radiohead could not play back-to-back if the artist spacing constraint were active. In a similar example, constraints may prevent songs from the same album or song title from occurring within a given number of songs of each other in a playlist. Another constraint would prevent songs from non-compatible genres from playing in the same playlist. Still yet another could be a “jitter” function. Jitter can randomly prevent a song that would otherwise be acceptable from being added to the playlist. Jitter provides randomness to a playlist to prevent the same playlist from being generated every time based the selection of the same seed track. Still yet another constraint could be a skip count constraint wherein any song that has been skipped more than a given number of times would fail the constraint and not be included in the playlist.
• It should be appreciated that the constraints are dependent on certain parameters or variables that can be easily varied. For example, the required number of intervening songs between two songs from the same album or artist can be varied. Similarly, the number of skip counts needed to exclude a track or the members of compatible genres can be varied. In one embodiment, such variable settings can be configured by the user. In another embodiment, such settings are chosen by and issue from the server and may be adjusted by the server whenever the client connects to download updated similarity data.
• It should also be appreciated that positive constraints are also contemplated. Songs with high play rates or high ratings can be moved up in the playlist or can be immune to the jitter function or effects of some other negative constraint. Many variations are possible by adding more restraints, removing constraints, making constraints more or less strict, each of which is contemplated by the method described herein.
• Instep810 the next candidate to be considered is selected and its metadata is retrieved instep812. The metadata provides information about the candidate that will be needed in evaluating the constraints. Insteps814,815, and816 the track is evaluated by the constraints. While only three constraints are represented inFIG. 18, it is contemplated that there can be any number of possible constraints. If the song passes one constraint, it is passed to the next constraint until all constraints are passed instep818 and the track is added to the playlist. Thereafter the method proceeds to step820 and fetches similarity data for the new song in the playlist. That similarity data can be appended to the candidate list for consideration for inclusion in the playlist.
• If a track fails a constraint the method skips to step830 and returns to step810 if there are additional candidates in the list to evaluate. However, if there are no additional candidates in the list, meaning that all candidates either failed the constraints or are in the playlist, step832 checks the constraints to determine if they are set to their default value. If they aren't, the constraints are relaxed atstep828 in the hope that relaxing one or more of the constraints will allow a previously rejected candidate to be added to the playlist upon reconsideration atstep826. If all candidates once again fail the constraints,step832 determines that the constraints were already relaxed and ends the process.
• Relaxing constraints can take any one of a variety of forms. In some cases only one constraint becomes less strict. In other cases multiple constraints are relaxed. For example, if the first constraint requires that two songs from the same artist do not play within 4 songs of each other, the constraint can be relaxed to only require one intervening song or the constraint can be eliminated entirely. In some embodiments, not all constraints can be relaxed. An example is the genre constraint. Certain genres may never be compatible and thus the genre constraint would not be relaxed to include additional genres.
• Returning to step826, in the instance where the candidate track failed the constraints and no additional candidates are available, the constraints are relaxed. If, due to the relaxed constraints, a candidate passes all constraints and is added to the playlist, the constraints are returned to normal atsteps822 and824. Step822 checks the constraints to determine if they are relaxed or are at their default settings. If they are at their default settings, the method returns to step810 and considers the next track in the list. If, however, step822 determines the constraints are relaxed, the method proceeds to step824 which returns the constraints to normal and then returns to step810 to consider the next candidate in the list. This process continues until no candidate passes the relaxed constraints and the routine ends atstep834.
• Songs need not be added to a playlist in order of the most similar to least similar; songs can be added in any order using a randomization algorithm or other logic.
• Generated playlists can be static or dynamic. Dynamic playlists can be updated over time as the similarity data evolves and as new items are added to a user's library. Alternatively, when a playlist is generated that a user enjoys and wants to retain without change, the user can save the playlist as a separate, static playlist which is no longer influenced by the similarity data. In this manner, when users feel that a particular generated playlist is “perfect”, it can be preserved unsullied from the changing tastes of the masses reflected in the similarity table through the server.
• Mixes from Participant Clusters
• The participant clusters are useful in generating mixes of media items. As an exemplary embodiment, the mixes can be music media item mixes.
• As discussed above, a client device downloads information regarding the clusters contained within the program participant's media library. While any number of clusters can exist, in some embodiments it is desired to only keep track of a limited number of clusters, for example twelve. Since each of the clusters includes media items that do not overlap with any other cluster, each cluster will represent different collections of similar media items. The result is that each of the twelve clusters can represent different types of music. A program participant might be in the mood to listen to their classical media items, or their popular media items and the clusters can create mixes from these collections.
• FIG. 19 illustrates the basic method for generating the mixes. Since the mixes are intended to be a representation of media items within the program participant's media library that are similar, an average similarity or affinity for the cluster is calculated865. This can be done in a number of different ways including taking an average of all similarity vectors for the media items represented in a cluster. The average vector will represent the average affinity of the media items for the cluster. An alternative method is to choose a media item for which the similarity scores of the other media items with respect to the chosen media items are strongly similar and use that media item as a representative media item for the cluster.
• The process can then select several songs (without any user involvement) from the cluster. Ideally, these items will have an approximately average similarity score to the cluster average so that the seed songs are representative of the cluster. In some embodiments it is desired to avoid selecting the most strongly correlated or the most weakly correlated items to the cluster. But, in some embodiments, the most strongly correlated items can be selected. And in some embodiments the selection of the several media items can be a random selection of media items from within the cluster.
• The selectedmedia items867 are input into aplaylist algorithm869 such as the one described above. Each of the selected items constitutes a seed track for the playlist algorithm. Since the playlist module will lookupsimilar items808,820 for all items in the playlist to use as candidates for inclusion into the playlist, the playlist may eventually include media items outside the cluster. Once the playlist is created, it is played871 until the program participant discontinues playback. As illustrated inFIG. 19, once the playlist has reached its end, the process continues so that the mix is endless. The result will be that media items that are generally similar to the other items in the selected cluster will continuously play.
Uses of Similarity Data for Syncing Devices
• Just as playlists can be generated, similarity data can also be used to keep a peripheral device such as a portable music player updated with new or different music from the user's media library. Many portable media players suffer from limited capacity and thus not all of a user's media library can be stored on a portable device such as an IPOD portable media player. In such instances users often must select a portion of their media items to be stored on their portable device. Some user's may consider this process burdensome and may find that they get tired of the media items that are currently stored on their portable device.
• One solution to the problem identified above is to use similarity data to keep the portable device updated with new media items. In this embodiment a user selects a certain number of seed tracks that represent the type of music that they would like on their portable device. Just as a playlist can be generated from seed tracks, so too can data items from a user's library be chosen for inclusion on a portable media player. As similarity data changes, and as new songs are added to a user's library, similarity data can be used to keep the portable device up-to-date with new tracks.
Purchase Recommendations
• Similarity data can also be used to recommend new items for purchase by a user. Items that occur in the master similarity table, but are not present in the user's library can be recommended for purchase by the system. In one embodiment the online store can make purchase recommendations based on the user's library or the selection of a seed track. The online store can also recommend items for purchase using recent purchases as the seed track. In another embodiment the playlist module can recommend songs for purchase by informing the user of where the song would have been included in the playlist if it were part of the user's library. Purchase recommendations can occur at any level of the system from the server to the client to the portable media player.
• Similarly, items in a sever cluster that are not owned by a program participant can be suggested for purchase to the program participant.
• In some embodiments, the item to be recommended can be a new item that does not yet have similarity data associated with it. In such a scenario, a similarity score can be provided by an administrator of the online store so that the new item will be recommended for purchase by users. The provided similarity score can remain until similarity data based on co-occurrence or other embodiments is available.
• Similarly, movie rentals or purchases could also be recommended. While most of the embodiments have been described with respect to songs, media items can also be any file including videos or movies. In this embodiment, a user can request similar movies based on the selection of a seed item. Alternatively, the system can recommend movies based on previous rentals. It is even contemplated that similarity data can be used to automatically download new movies to a client or portable media player for the user's viewing at a later time. This embodiment could be part of a subscribed service or the user could choose to not watch the movie and not-incur a rental fee.
• FIG. 20 illustrates one method embodiment in which similarity data can be used for recommending media items for purchase. Instep1002, a seed track is selected. Purchase recommendations are based off of a seed track, just as playlists are generated based on a seed track. However, in at least one embodiment, purchase recommendations can be based on content most similar to a user's entire library.
• Once a seed track is selected, the illustrated method next looks up similarity data for that seed track from the individual similarity table instep1004. In this embodiment, it will be appreciated that the individual similarity table will also contain media items that are not in the user's library, but are related by similarity data to items that are present in the user's media library. In another embodiment, the purchase recommendation can come directly from the server, rather than the locally stored similarity table. Similarity lists from the master similarity table can provide similarity data and the server or client can subtract out the tracks identified from the user's library. This embodiment has the benefit of generating the smallest possible individual similarity tables, since purchase recommendations do not need to be included, and all users share the master table for recommendation purposes.
• To prevent the items that are already in a user's library from being recommended for purchase,step1006 filters items that are already in the user's media library from the similarity data retrieved instep1004. In some cases media items have already been purchased by a user, but those items are not in the user's media library. This could be for any number of reasons such as: the user did not like the song and deleted it, or the user has stored the media item in another library, or the user may have purchased the media item but has not downloaded it yet. In at least these scenarios it would not be desirable to recommend these media items for purchase, so they too are filtered out instep1008.Step1010 displays the recommended items for purchase.
• Of course, the method can repeat for every song that is currently selected by the user. In some embodiments, the user need not affirmatively seek purchase recommendations. In such embodiments, purchase recommendations can be displayed within a media organizer or media store whenever a media item is selected for playback. As the media item is played, a graphical user interface can display other recommended media items, or groups of media items, such as albums, for purchase. In a preferred embodiment, the media items can be purchased directly by selecting, with an input device, the recommendation itself, or at least the recommendation can hyperlink to an online store so that the media item can be purchased therefrom.
• In another embodiment, purchase recommendations can also be shown using this methodology where a selection is not available. For example, in a View An Artist page which would display top songs by a designated artist that listeners have also bought, the system can display recommendations that are filtered to eliminate recommendations of items already in the user's library.
Server>Client>Ipod
• In one particularly preferred embodiment, the methods that are useful at one location are equally applicable at each location in the system.FIG. 21 illustrates this concept. Anonline music store902 is shown containing a similarity table908 and aplaylist module914. The similarity table908 contains all of the relationships for each item in the server's media inventory. Theplaylist module914 operates based on the data in the similarity table just as it would on any other client or portable media player in the system. Likewise, theclient904 is shown containing a smaller media inventory than the server contains and similarity data for each item in the client's media inventory is stored in its similarity table910.Playlist module916 operates based on the data in the local similarity table910 just as it would on theportable media player906 ormusic store902. Finally,portable media player906 is shown containing a smaller media inventory than that of theclient904. The similarity table912 stores information relevant to items in the portable media player's906 media inventory and theplaylist module918 operates based on that data.
• FIG. 21 illustrates the concept that the client can behave like a server to a group of portable media players or a larger client can behave as a server to smaller clients; all of which is contemplated herein.
• In most embodiments, the server will be the only location maintaining the master purchase matrix and master similarity table, but the generation of local similarity tables can occur on any device based on the data derived from the server. Another function that will likely be carried out by the server is updating. Not only will the server be the source of similarity data updates in most embodiments, but the server can also update the playlist module or software components of the system.
• It will be appreciated that not all processes described herein must occur in real time. In many cases it will be desirable to save processing resources and carry out certain tasks offline. For example, the collaboration filter engine may run only at scheduled times to generate the master similarity data table. It is further conceived that the need for offline processing may be relieved as technology advances. In such instances, those processes that are now preferred to be carried out offline could be carried out in real time.
• In another embodiment, although each device is capable of carrying out certain functions locally, it may be desirable to have the server carry out specified tasks. For example, the server could generate individual similarity tables for the client or generate playlists for the client. This may be of greater use for the client to carry out these tasks for the portable media player which typically lacks the processing resources desired for large processes. In another example, it might be beneficial for the server to carry out some of the constraints used in playlist generation and incorporate the results in the similarity table data. For example, in the case of a genre constraint which will never be relaxed, the server may exclude media items from a non-compatible genre from an item's similarity data. In this way, the playlist module will not need to run the constraint when generating a playlist because the server would have already excluded items that would not pass the constraint from the individual similarity table.
• FIG. 22 illustrates an example system for syncing media and similarity tables to a digital media player. Thecommunication medium920 is most likely to be the Internet, but can include any channel(s) allowing devices to communicate with each other. Theonline store922 communicates with aclient924, typically a personal computer, with special software installed to communicate and interact with the online store. Aportable media player926, such as an Apple IPOD media player, typically syncs via a 30-pin USB connector with apersonal computer924 connected to theonline store922. Other ways to connect aportable media player926 to apersonal computer924 include USB, Firewire, 802.11 series or Bluetooth wireless connections. The online store has a master library ofmedia930, a master similarity table932, and a tree ofserver clusters931. When theportable media player926 is synced, thelocal media934 metadata and the local subset similarity table936 andparticipant server clusters935 are transmitted through thepersonal computer924 and thecommunication medium920 to theonline store922. It is important to note that only metadata is transmitted, not the actual media. The online store does not need a copy of the media, it only needs sufficient information to positively identify which media are located on theportable media player926. The online store is able to generate and/or retrieve the appropriate information and send it back to the device, updating the local subset similarity table936 andparticipant clusters935 with fresh data corresponding to the locally storedmedia934. The local subset similarity table is then used to generate individualized playlists at the online store level, the computer level, and/or on the device itself.
• In another embodiment theportable media player926 can obtain data directly from theserver922. In such an embodiment the portable media player can be equipped with various capabilities for connecting to the online store such as through 802.11 series communications (Wi-Fi) or through a mobile telephone network. The portable media player can connect directly to a server and perform just as a client device would in the example above. The portable media can be assigned a unique identification number, or if the library is also associated with a client device, the portable media player can use the same identification number as would the client device. Regardless, the portable media player can upload information about media items stored in its library and download similarity data about those same items. It should be appreciated that the portable media player can have more than one method of connecting to the server. Not only can the portable media player have multiple mechanisms for connecting to an online store, but the portable media player can also have capabilities to synchronize with a client device and communicate directly with the online store.
• Embodiments within the scope of the present invention may also include computer-readable media for carrying or having computer-executable instructions or data structures stored thereon. Such computer-readable media can be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code means in the form of computer-executable instructions or data structures. Combinations of the above should also be included within the scope of the computer-readable media.
• Computer-executable instructions include, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing device to perform a certain function or group of functions. Computer-executable instructions also include program modules that are executed by computers in stand-alone or network environments. Generally, program modules include routines, programs, objects, components, and data structures that perform particular tasks or implement particular abstract data types. Computer-executable instructions, associated data structures, and program modules represent examples of the program code means for executing steps of the methods disclosed herein. The particular sequence of such executable instructions or associated data structures represent examples of corresponding acts for implementing the functions described in such steps.
• Those of skill in the art will appreciate that other embodiments of the invention may be practiced in network computing environments with many types of computer system configurations, including personal computers, hand-held devices, multi-processor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, and the like. Embodiments may also be practiced in distributed computing environments where tasks are performed by local and remote processing devices that are linked (either by hardwired links, wireless links, or by a combination thereof) through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices.
• Communication at various stages of the described system can be performed through a network cloud328 (shown inFIG. 16) such as a local area network, a token ring network, the Internet, a corporate intranet, 802.11 series wireless signals, fiber-optic network, radio or microwave transmission, etc. Although the underlying communication technology may change, the fundamental principles described herein are still applicable.
• The various embodiments described above are provided by way of illustration only and should not be construed to limit the invention. For example, the principles herein may be applied to an online store accessible wirelessly by a portable media playback device or by a personal computer physically connected to a network. Those skilled in the art will readily recognize various modifications and changes that may be made to the present invention without following the example embodiments and applications illustrated and described herein, and without departing from the true spirit and scope of the present disclosure.

Claims (31)

1. A computer implemented method for clustering similar media items in a program participant's media library comprising:

dividing a collection of media items that each exist in at least one program participant's media library of a population of program participants into canopies comprising respective groups of potentially similar media items;

recursively sub-dividing the media items in each canopy, each recursion producing non-overlapping, increasingly refined, server clusters of media items determined to be similar to other items in a respective server cluster based on a cluster analysis of similarity data derived from the population of program participants;

terminating the recursive sub-dividing responsive to determining that the server clusters produced from the latest recursion each comprise no more than a determined number of media items, resulting in a plurality of lowest-lowest server clusters; and

creating one or more media item clusters for a particular program participant from items present in that program participant's media library, comprising:

determining respective participant media item clusters for media items found in that program participant's media library from their membership in any of the lowest-level server clusters; and

recursively agglomerating participant clusters that share a common parent server cluster, and which have fewer than a participant cluster minimum number of media items, into respective larger participant clusters until each of those larger participant clusters comprises at least the participant cluster minimum number of media items.

2. The method ofclaim 1, wherein the canopies divide the program participants' collective media library inventories into groupings based on editorial data from which it can be concluded that media items in different groupings can never be considered similar.

3. The method ofclaim 2, wherein the editorial data comprises genre information.

4. The method ofclaim 1, wherein the cluster analysis comprises a k-means analysis.

5. The method ofclaim 1, wherein the media items in each canopy are grouped by artist before the cluster analysis.

6. The method ofclaim 1, wherein the determined number of media items in a lowest-level server cluster is 1000 or less.

7. The method ofclaim 1, wherein the determined number of media items in a lowest-level server cluster is 100 or less.

8. The method ofclaim 1, wherein the determined number of media items in a lowest-level server cluster is 50 or less.

9. The method ofclaim 1, wherein the participant cluster minimum number of media items comprising is equal to or greater than 20 items.

10. The method ofclaim 1, wherein the participant cluster minimum number of media items comprising a participant cluster is equal to or greater than 50 items.

11. The method ofclaim 1, wherein the similarity data derived from the population of program participants comprises a vector space, wherein each vector within the vector space represents a media item and all media items similar to the media item.

12. A method of creating mixes of media items from a program participant's collection of media items comprising:

sending to a server, information describing individual media items of a program participant's collection of media items;

receiving from the server, data describing clusters of media items contained within the program participant's collection of media items, the clusters having been compiled based on an agglomeration of tracks found in hierarchically related clusters of media items in a media item inventory available to the server, the clusters of media items in the inventory having been determined based on a cluster analysis of similarity data derived from a population of program participants; and

determining a mix of media items, the mix comprising media items selected from one of the clusters of media items contained within the program participant's collection of media items received from the server.

13. The method ofclaim 12, wherein the mix of media items comprises a playlist generated from songs selected from one of the clusters and songs similar to the songs selected from one of the clusters.

14. The method ofclaim 12, wherein the songs comprising the mix of media items are chosen based on a degree of similarity between each of the songs and the one cluster.

15. The method ofclaim 12, wherein the similarity data derived from the population of program participants comprises a vector space, wherein each vector within the vector space represents a media item and all media items similar to the media item.

16. A device comprising:

a media storage unit configured to store data describing clusters of media items stored in a program participant's collection of media items, the clusters having been compiled based on an agglomeration of tracks found in hierarchically related clusters of media items available from a server inventory, the clusters of media items in the server inventory having been determined based on a cluster analysis of similarity data derived from a population of program participants;

a tangible computer readable medium storing instructions for configuring a processor to select a mix of media items selected from media items identified in one of the clusters of media items in the program participant's collection of media items; and

a processor to be configured by instructions obtained from the computer readable medium.

17. The device ofclaim 16 further comprising:

a communications interface configured to send to the server, information describing individual media items contained with a program participant's collection of media items, and further configured to receive, from the server, the data describing the clusters of media items in the program participants collection of media items.

18. The device ofclaim 17, wherein the cluster data comprises information identifying a plurality of clusters and media items identified within each of the plurality of clusters.

19. The device ofclaim 17, wherein the mix comprises a list of similar media items generated from the cluster data.

20. A system for clustering similar media items in a program participant's media library comprising:

a server configured to recursively sub-divide a collection of media items formed from the media items that exist in at least one program participant's media library of a population of program participants, each recursive sub-division producing non-overlapping, increasingly refined, server clusters of media items determined to be similar to other items in a respective server cluster based on a cluster analysis of similarity data derived from the media libraries of the population of program participants and to terminate the recursive sub-dividing responsive to a determination that the server clusters produced from the latest recursive sub-division each comprise no more than a determined number of media items;

a server configured to create one or more media item clusters for a particular program participant from items present in that program participant's media library based on the server clusters, by performing a method comprising: determining participant clusters for media items from that program participant's media library that are found in one or more lowest-level server cluster, and recursively agglomerating, into larger participant clusters, participant clusters that share a common parent server cluster until each of those larger participant clusters comprises at least a determined minimum number of media items; and

a media playing device configured to generate a mix of similar media items for playback based on a selection of media items represented in one of the participant clusters.

21. The system ofclaim 20, wherein the servers make up part of one server array.

22. The system ofclaim 20, wherein the servers comprise the same server.

23. The system ofclaim 20, wherein the similarity data derived from the population of program participants comprises a vector space, wherein each vector within the vector space represents occurrences of an individual media item in each program participant's media library.

24. The system ofclaim 20, wherein the similarity data derived from the population of program participants comprises a similarity matrix representing incidences of co-occurrences of an individual media items in among program participants' media libraries.

25. A machine-readable medium having stored thereon machine-readable instructions for causing a machine to perform a method comprising:

recursively sub-dividing a collection of media items that each exist in at least one program participant's media library of a population of program participants, each recursion producing non-overlapping, increasingly refined, server clusters of media items determined to be similar to other items in a respective server cluster based on a cluster analysis of similarity data derived from the population of program participants;

terminating the recursive sub-dividing responsive to determining that the server clusters produced from the latest recursive sub-division all comprise no more than a determined number of media items; and

creating one or more media item clusters for a particular program participant from items present in that program participant's media library, comprising:

forming respective participant clusters of media items found in that program participant's media library based on membership of those media items in respective lowest-level server clusters; and

recursively agglomerating participant clusters that share a common parent server cluster into larger participant clusters until each of those larger participant clusters comprises at least a determined minimum number of media items.

26. The machine-readable medium ofclaim 25, wherein the method further comprises

dividing the collection of media items that each exist in at least one program participant's media library of a population of program participants into canopies comprising respective groups of potentially similar media items, wherein items in different canopies cannot be divided into the same server cluster.

27. The machine-readable medium ofclaim 26, wherein the canopies are determined based on editorial data.

28. The machine-readable medium ofclaim 27, wherein the editorial data comprises genre information.

29. The machine-readable medium ofclaim 25, wherein the cluster analysis comprises a k-means analysis.

30. A machine-readable medium having stored thereon machine-readable instructions for causing a machine to perform a method comprising:

sending to a server, information describing individual media items contained with a program participant's collection of media items;

receiving from the server, data defining clusters of the media items contained within the program participant's collection of media items, the clusters having been compiled based on an agglomeration of tracks found in hierarchically related clusters of media items in a server inventory, the clusters of media items in the server's inventory having been determined based on a cluster analysis of similarity data derived from a population of program participants; and

determining a mix of media items, the mix comprising media items represented in one of the clusters of media items contained within the program participant's collection of media items received from the server.

31. The machine-readable medium ofclaim 30, wherein each of the clusters identifies a determined minimum number of items, and the cluster was formed by agglomerating increasingly dissimilar items until the cluster identified the minimum number of items.

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