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Network Working Group                                           J. AllenRequest for Comments: 2651                                WebTV NetworksCategory: Standards Track                                    M. Mealling                                                 Network Solutions, Inc.                                                             August 1999The Architecture of the Common Indexing Protocol (CIP)Status of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (1999).  All Rights Reserved.Abstract   The Common Indexing Protocol (CIP) is used to pass indexing   information from server to server in order to facilitate query   routing. Query routing is the process of redirecting and replicating   queries through a distributed database system towards servers holding   the desired results. This document describes the CIP framework,   including its architecture and the protocol specifics of exchanging   indices.1. Introduction1.1. History and Motivation   The Common Indexing Protocol (CIP) is an evolution and refinement of   distributed indexing concepts first introduced in the Whois++   Directory Service [RFC1913,RFC1914]. While indexing proved useful in   that system to promote query routing, the centroid index object which   is passed among Whois++ servers is specifically designed for   template-based databases searchable by token-based matching.  With   alternative index objects, the index-passing technology will prove   useful to many more application domains, not simply Directory   Services and those applications which can be cast into the form of   template collections.Allen & Mealling            Standards Track                     [Page 1]

RFC 2651                  The CIP Architecture               August 1999   The indexing part of Whois++ is integrated with the data access   protocol. The goal in designing CIP is to extract the indexing   portion of Whois++, while abstracting the index objects to apply more   broadly to information retrieval. In addition, another kind of   technology reuse has been undertaken by converting the ad-hoc data   representations used by Whois++ into structures based on the MIME   specification for structured Internet mail.   Whois++ used a version number field in centroid objects to facilitate   future growth. The initial version was "1". Version 1 of CIP (then   embedded in Whois++, and not referred to separately as CIP) had   support for only ISO-8895-1 characters, and for only the centroid   index object type.   Version 2 of the Whois++ centroid was used in the Digger software by   Bunyip Information Systems to notify recipients that the centroid   carried extra character set information. Digger's centroids can carry   UTF-8 encoded 16-bit Unicode characters, or ISO-8859-1 characters,   determined by a field in the headers.   This specification is for CIP version 3.  Version 3 is a major   overhaul to the protocol.  However, by using of a short negotiation   sequence, CIP version 3 servers can interoperate with earlier servers   in an index-passing mesh.   For unclear terms the reader is referred to the glossary inAppendixA.1.2 CIP's place in the Information Retrieval world   CIP facilitates query routing. CIP is a protocol used between servers   in a network to pass hints which make data access by clients at a   later date more efficient. Query routing is the act of redirecting   and replicating queries through a distributed database system towards   the servers holding the actual results via reference to indexing   information.   CIP is a "backend" protocol -- it is implemented in and "spoken" only   among network servers. These same servers must also speak some kind   of data access protocol to communicate with clients. During query   resolution in the native protocol implementation, the server will   refer to the indexing information collected by the CIP implementation   for guidance on how to route the query.   Data access protocols used with CIP must have some provision for   control information in the form of a referral. The syntax and   semantics of these referrals are outside the scope of this   specification.Allen & Mealling            Standards Track                     [Page 2]

RFC 2651                  The CIP Architecture               August 19992. Related Documents   This document is one of three documents. This document describes the   fundamental concepts and framework of CIP.   The document "MIME Object Definitions for the Common Indexing   Protocol" [CIP-MIME] describes the MIME objects that make up the   items that are passed by the transport system.   Requirements and examples of several transport systems are specified   in the "CIP Transport Protocols" [CIP-TRANSPORT] document.   A second set of document describe the various specifications for   specific index types.3. Architecture3.1 CIP in the Information Retrieval World3.1.1 Information Retrieval in the Abstract   In order to better understand how CIP fits into the information   retrieval world, we need to first understand the unifying abstract   features of existing information retrieval technology. Next, we   discuss why adding indexing technology to this model results in a   system capable of query routing, and why query routing is useful.   An abstract view of the client/server data retrieval process includes   data sets and data access protocols. An individual server is   responsible for handling queries over a fixed domain of data. For the   purposes of CIP, we call this domain of data the dataset. Clients   make searches in the dataset and retrieve parts of it via a data   access protocol. There are many data access protocols, each optimized   for the data in question. For instance, LDAP and Whois++ are access   protocols that reflect the needs of the directory services   application domain. Other data access protocols include HTTP and   Z39.50.3.1.2 Indexing Information Facilitates Query Routing   The above description reflects a world without indexing, where no   server knows about any other server. In some cases (as with X.500   referrals, and HTTP redirects) a server will, as part of its reply,   implicate another server in the process of resolving the query.   However, those servers generate replies based solely on their local   knowledge. When indexing information is introduced into a server's   local database, the server now knows not only answers based on theAllen & Mealling            Standards Track                     [Page 3]

RFC 2651                  The CIP Architecture               August 1999   local dataset, but also answers based on external indices. These   indices come from peer servers, via an indexing protocol. CIP is one   such indexing protocol.   Replies based on index information may not be the complete answer.   After all, an index is not a replicated version of the remote   dataset, but a possibly reduced version of it. Thus, in addition to   giving complete replies from the local dataset, the server may give   referrals to other datasets. These referrals are the core feature   necessary for effective query routing. When servers use CIP to pass   indices from server to server, they make a kind of investment. At the   cost of some resources to create, transmit and store the indices,   query routing becomes possible.   Query Routing is the process of replicating and moving a query closer   to datasets which can satisfy the query. In some distributed systems,   widely distributed searches must be accomplished by replicating the   query to all sub-datasets. This approach can be wasteful of resources   both in the network, and on the servers, and is thus sometimes   explicitly disabled. Using indexing in such a system opens the door   to more efficient distributed searching.   While CIP-equipped servers provide the referrals necessary to make   query routing work, it is always the client's responsibility to   collate, filter, and chase the referrals it receives. This gives the   end-user (or agent, in the case that there's no human user involved   in the search) greatest control over the query resolution process.   The cost of the added client complexity is weighed against the   benefits of total control over query resolution. In some cases, it   may also be possible to decouple the referral chasing from the client   by introducing a proxy, allowing existing simple clients to make use   of query routing. Such a proxy would transparently resolve referrals   into concrete results before returning them to the simple-minded   client.3.1.3 Abstracting the CIP index object   As useful as indices seem, the fact remains that not all queries can   benefit from the same type of index. For example, say the index   consists of a simple list of keywords. With such an index, it is   impossible to answer queries about whether two keywords were near one   another, or if a keyword was present in a certain context (for   instance, in the title).   Because of the need for application domain specific indices, CIP   index objects are abstract; they must be defined by a separate   specification. The basic protocols for moving index objects are   widely applicable, but the specific design of the index, and theAllen & Mealling            Standards Track                     [Page 4]

RFC 2651                  The CIP Architecture               August 1999   structure of the mesh of servers which pass a particular type of   index is dependent on the application domain. This document describes   only the protocols for moving indices among servers. Companion   documents describe initial index objects.   The requirements that index type specifications must address are   specified in the [CIP-MIME] document.3.2 Architectural Details   CIP implements index passing, providing the forward knowledge   necessary to generate the referrals used for query routing. The core   of the protocol is the index object. In the following sections, the   structure of the index objects themselves is presented. Next, how and   why indices are passed from server to server is discussed. Finally,   the circumstances under which a server may synthesize an index object   based on incoming ones are discussed.3.2.1 The CIP Index Object   A CIP index object is composed of two parts, the header and the   payload. The header contains metadata necessary to process and make   use of the index object being transmitted. The actual index resides   in the payload.   Three particular headers warrant specific mention at this point.  The   "type" of the index object selects one of many distinct CIP index   object specifications which define exactly how the index blocks are   to be created, parsed and used to facilitate query routing.  Another   header of note is the "DSI", or Dataset Identifier, which uniquely   identifies the dataset from which the index was created.  Another   header that is crucial for generating referrals is the "Base-URI".   The URI (or URI's) contained in this header form the basis of any   referrals generated based on this index block. The URI is also used   as input during the index aggregation process to constrain the kinds   of aggregation possible, due to multiprotocol constraints.  How that   URI is used is defined by the aggregation algorithm.  The exact   syntax of these headers is specified in the CIP MIME specification   document [CIP-MIME].   The payload is opaque to CIP itself. It is defined exclusively by the   index object specification associated with the object's MIME type.   Specifications on how to parse and use the payload are published   separately as "CIP index object specifications". This abstract   definition of the index object forms the basis of CIP's applicability   to indexing needs across multiple application domains.Allen & Mealling            Standards Track                     [Page 5]

RFC 2651                  The CIP Architecture               August 1999   A precise definition of the content and form of a CIP index block can   be found in the Protocol document [CIP-MIME]3.2.2 Moving Index Objects: How to Build a Mesh   Indices are transmitted among servers participating in a CIP mesh. By   distributing this information in anticipation of a query, efficient,   accurate query routing is possible at the time a query arrives.   A CIP mesh is a set of CIP servers which pass indices of the same   type among themselves. Typically, a mesh is arranged in a   hierarchical tree fashion, with servers nearer the root of the tree   having larger and more comprehensive indices. See Figure 1. However,   a CIP mesh is explicitly allowed to have lateral links in it, and   there may be more than one part of the mesh that has the properties   of a "root". Mesh administrators are encouraged to avoid loops in the   system, but they are not obliged to maintain a strict tree structure.   Clients wishing to completely resolve all referrals they receive   should protect against referral loops while attempting to traverse   the mesh to avoid wasting time and network resources.  See the   section on "Navigating the Mesh" for a discussion of this.Allen & Mealling            Standards Track                     [Page 6]

RFC 2651                  The CIP Architecture               August 1999     base level             index                    index     directory             servers                  servers      servers                for                      for                          base level               lower-level                           servers                index servers     _______    |       |    |   A   |__    |_______|  \            _______                \---CIP----|       |     _______               |   D   |__    |       |   /---CIP----|_______|  \             ------    |   B   |__/                       \--CIP------|      |    |_______|                                      |  F   |                                       /--CIP------|______|                                      /     _______                _______  /    |       |              |       |-    |   C   |-------CIP----|   E   |    |_______|              |_______|-                                |    \                                r     \     _______                    e      \            ______    |       |                   f       \--CIP-----|      |    |   G   |-------CIP---------e------------------|  H   |    |_______|                   r                  |______|            \--referral---|     r      --referral-/                          |     a     |                          |     l     |                          \ 3   | 2   | 1                            \--------/                            |        |                            | client |                            |        |                             --------             Figure 1: Sample layout of the Index Service meshAllen & Mealling            Standards Track                     [Page 7]

RFC 2651                  The CIP Architecture               August 1999   All indices passed in a given mesh are assumed, as of this writing,   to be of the same type (i.e. governed by the same CIP index object   specification). It may be possible to create gateways between meshes   carrying different index objects, but at this time that process is   undefined and declared to be outside the scope of this specification.   In the case where a CIP server receives an index of a type that it   does not understand it _can_ pass that index forward untouched.  In   the case where a server implementation decides not to accept unknown   indices it should return an appropriate error message to the server   sending the index. This behavior is to allow mesh implementations to   attempt heterogeneous meshes. As stated above heterogeneous meshes   are considered to be ill defined and as such should be considered   dangerous.   Experience suggests that this index passing activity should take   place among CIP servers as a parallel (and possibly lower-priority)   job to their primary job of answering queries. Index objects travel   among CIP servers by protocol exchanges explicitly defined in this   document, not via the server's native protocol. This distinction is   important, and bears repeating:      Queries are answered (and referrals are sent) via the native data      access protocol.      Index objects are transferred via alternative means, as defined by      this document.   When two servers cooperate to move indexing information, the pair are   said to be in a "polling relationship". The server that holds the   data of interest, and generates the index is called the "polled   server".  The other server, which is the one that collects the   generated index, is the "polling server".   In a polling relationship, the polled server is responsible for   notifying the polling server when it has a new index that the polling   server might be interested in. In response, the polling server may   immediately pick up the index object, or it may schedule a job to   pick up a copy of the new index at a more convenient time. But, a   polling server is not required to wait on the polled server to notify   it of changes. The polling server can request a new index at any   time.   Independent of the symmetric polling relationship, there's another   way that servers can pass indices using CIP. In an "index pushing"   relationship, a CIP server simply sends the index to a peer whenever   necessary, and allows the receiver to handle the index object as itAllen & Mealling            Standards Track                     [Page 8]

RFC 2651                  The CIP Architecture               August 1999   chooses. The receiving server may refuse it, may accept it, then   silently discard it, may accept only portions of it (by accepting it   as is, then filtering it), or may accept it without question.   The index pushing relationship is intended for use by dumb leaf nodes   which simply want to make their index available to the global mesh of   servers, but have no interest in implementing the complete CIP   transaction protocol. It lowers the barriers to entry for CIP leaf   nodes. For more information on participating in a CIP mesh in this   restricted manner, see the section below on "Protocol Conformance".   CIP index passing operations take place across a reliable transport   mechanisms, including both TCP connections, and Internet mail   messages. The precise mechanisms are described in the Transport   document [CIP-Transport].3.2.3 Index Object Synthesis   From the preceding discussion, it should be clear that indexing   servers read and write index objects as they pass them around the   mesh. However, a CIP server need not simply pass the in-bound indices   through as the out-bound ones. While it is always permissible to pass   an index object through to other servers, a server may choose to   aggregate two or more of them, thereby reducing redundancy in the   index, at the cost of longer referral chains.   A basic premise of index passing is that even while collapsing a body   of data into an index by lossy compression methods, hints useful to   routing queries will survive in the resulting index. Since the index   is not a complete copy of the original dataset, it contains less   information. Index objects can be passed along unchanged, but as more   and more information collects in the resulting index object,   redundancy will creep in again, and it may prove useful to apply the   compression again, by aggregating two or more index objects into one.   This kind of aggregation should be performed without compromising the   ability to correctly route queries while avoiding excessive numbers   of missed results. The acceptable likelihood of false negatives must   be established on a per-application-domain basis, and is controlled   by the granularity of the index and the aggregation rules defined for   it by the particular specification.   However, when CIP is used in a multi-protocol application domain,   such as a Directory Service (with contenders including Whois++, LDAP,   and Ph), things get significantly trickier. The fundamental problem   is to avoid forcing a referral chain to pass through part of the mesh   which does not support the protocol by which that client made the   query. If this ever happens, the client loses access to any hitsAllen & Mealling            Standards Track                     [Page 9]

RFC 2651                  The CIP Architecture               August 1999   beyond that point in the referral chain, since it cannot resolve the   referral in its native data access protocol. This is a failure of   query routing, which should be avoided.   In addition to multi-protocol considerations, server managers may   choose not to allow index object aggregation for performance reasons.   As referral chains lengthen, a client needs to perform more   transactions to resolve a query. As the number of transactions   increases, so do the user-perceived delays, the system loads, and the   global bandwidth demands. In general, there's a tradeoff between   aggressive aggregation (which leads to reductions in the indexing   overhead) and aggressive referral chain optimization. This tradeoff,   which is also sensitive to the particular application domain, needs   to be explored more in actual operational situations.   Conceptually, a CIP index server has several index objects on hand at   any given time. If it holds data in addition to indexing information,   the server has an index object formed from its own data, called the   "local index". It may have one or more indices from remote servers   which it has collected via the index passing mechanisms. These are   called "in-bound indices".      Implementor's Note: It may not be necessary to keep all of these      structures intact and distinct in the local database. It is also      not required to keep the out-bound index (or indices) built and      ready to distribute at all times. The previous paragraph merely      introduces a useful model for expressing the aggregation rules.      Implementors are free to model index objects internally however      they see fit.   The following two rules control how a CIP server formulates its   outgoing indices:   1. An index server may pass any of the index objects in its local      index and its in-bound indices through unchanged to polling      servers.   2. If and only if the following three conditions are true, an index      server can aggregate two or more index objects into a single new      index object, to be added to the set of out-bound indices.      a. Each index object to be aggregated covers exactly the same set         of protocols, as defined by the scheme component of the Base-         URI's in each index object.      b. The index server supports every one of the data access         protocols represented by the Base-URI's in the index objects to         be aggregated.Allen & Mealling            Standards Track                    [Page 10]

RFC 2651                  The CIP Architecture               August 1999      c. The specification for the index object type specified by the         type header of the index objects explicitly defines the         aggregation operation.      The resulting index object must have Base-URI's characteristic of      the local server for each protocol it supports. The outgoing      objects should have the DSI of the local server.4. Navigating the mesh   With the CIP infrastructure in place to manage index objects, the   only problem remaining is how to successfully use the indexing   information to do efficient searches. CIP facilitates query routing,   which is essentially a client activity. A client connects to one   server, which redirects the query to servers "closer to" the answer.   This redirection message is called a referral.4.1 The Referral   The concept of a referral and the mechanism for deciding when they   should be issued is described by CIP. However, the referral itself   must be transferred to the client in the native protocol, so its   syntax is not directly a CIP issue. The mechanism for deciding that a   referral needs to be made and generating that referral resides in the   CIP implementation in the server. The mechanism for sending the   referral to the client resides in the server's native protocol   implementation.   A referral is made when a search against the index objects held by   the server shows that there may be hits available in one of the   datasets represented by those index objects. If more that one index   object indicates that a referral must be generated to a given   dataset, the server should generate only one referral to the given   dataset, as the client may not be able to detect duplicates.   Though the format of the referral is dependent on the native   protocol(s) of the CIP server, the baseline contents of the referral   are constant across all protocols. At the least, a DSI and a URI must   be returned.  The DSI is the DSI associated with the dataset which   caused the hit.  This must be presented to the client so that it can   avoid referral loops. The Base-URI parameter which travels along with   index objects is used to provide the other required part of a   referral.   The additional information in the Base-URI may be necessary for the   server receiving the referred query to correctly handle it. A good   example of this is an LDAP server, which needs a base X.500   distinguished name from which to search. When an LDAP server sends aAllen & Mealling            Standards Track                    [Page 11]

RFC 2651                  The CIP Architecture               August 1999   centroid-format index object up to a CIP indexing server, it sends a   Base-URI along with the name of the X.500 subtree for which the index   was made. When a referral is made, the Base-URI is passed back to the   client so that it can pass it to the original LDAP server.   As usual, in addition to sending the DSI, a DSI-Description header   can be optionally sent. Because a client may attempt to check with   the user before chasing the referral, and because this string is the   friendliest representation of the DSI that CIP has to offer, it   should be included in referrals when available (i.e. when it was sent   along with the index object).4.2 Cross-protocol Mappings   Each data access protocol which uses CIP will need a clearly defined   set of rules to map queries in the native protocol to searches   against an index object. These rules will vary according to the data   domain. In principle, this could create a bit of a scaling   difficulty; for N protocols and M data domains, there would be N x M   mappings required. In practice, this should not be the case, since   some access protocols will be wholly unsuited to some data domains.   Consider for example, a LDAP server trying to make a search in an   index object composed from unorganized text based pages. What would   the results be? How would the client make sense of the results?   However, as pre-existing protocols are connected to CIP, and as new   ones are developed to work with CIP, this issue must be examined. In   the case of Whois++ and the CENTROID index type, there is an   extremely close mapping, since the two were designed together. When   hooking LDAP to the CENTROID index type, it will be necessary to map   the attribute names used in the LDAP system to attribute names which   are already being used in the CENTROID mesh. It will also be   necessary to tokenize the LDAP queries under the same rules as the   CENTROID indexing policy, so that searches will take place correctly.   These application- and protocol-specific actions must be specified in   the index object specification, as discussed in the [CIP-MIME]   document.4.3 Moving through the mesh   From a client's point of view, CIP simply pushes all the "hard work"   onto its shoulders. After all, it is the client which needs to track   down the real data.  While this is true, it is very misleading.   Because the client has control over the query routing process, the   client has significant control over the size of the result set, the   speed with which the query progresses, and the depth of the search.Allen & Mealling            Standards Track                    [Page 12]

RFC 2651                  The CIP Architecture               August 1999   The simplest client implementation provides referrals to the user in   a raw, ready-to-reuse form, without attempting to follow them. For   instance, one Whois++ client, which interacts with the user via a   Web-based form, simply makes referrals into HTML hypertext links.   Encoded in the link via the HTML forms interface GET encoding rules   is the data of the referral: the hostname, port, and query. If a user   chooses to follow the referral link, he executes a new search on the   new host. A more savvy client might present the referrals to the user   and ask which should be followed. And, assuming appropriate limits   were placed on search time and bandwidth usage, it might be   reasonable to program a client to follow all referrals automatically.   When following all referrals, a client must show a bit of   intelligence.  Remember that the mesh is defined as an interconnected   graph of CIP servers. This graph may have cycles, which could cause   an infinite loop of referrals, wasting the servers' time and the   client's too. When faced with the job of tacking down all referrals,   a client must use some form of a mesh traversal algorithm. Such an   algorithm has been documented for use with Whois++ inRFC-1914. The   same algorithm can be easily used with this version of CIP. In   Whois++ the equivalent of a DSI is called a handle. With this   substitution, the Whois++ mesh traversal algorithm works unchanged   with CIP.   Finally, the mesh entry point (i.e. the first server queried) can   have an impact on the success of the query. To avoid scaling issues,   it is not acceptable to use a single "root" node, and force all   clients to connect to it. Instead, clients should connect to a   reasonably well connected (with respect to the CIP mesh, not the   Internet infrastructure) local server. If no match can be made from   this entry point, the client can expand the search by asking the   original server who polls it. In general, those servers will have a   better "vantage point" on the mesh, and will turn up answers that the   initial search didn't. The mechanism for dynamically determining the   mesh structure like this exists, but is not documented here for   brevity. SeeRFC-1913 for more information on the POLLED-BY and   POLLED-FOR commands.   It still should be noted that, while these mesh operations are   important to optimizing the searches that a client should make, the   client still speaks its native protocol. This information must be   communicated to the client without causing the client to have to   understand CIP.Allen & Mealling            Standards Track                    [Page 13]

RFC 2651                  The CIP Architecture               August 19995. Security Considerations   In this section, we discuss the security considerations necessary   when making use of this specification. There are at least three   levels at which security considerations come into play. Indexing   information can leak undesirable amounts of proprietary information,   unless carefully controlled. At a more fundamental level, the CIP   protocol itself requires external security services to operate in a   safe manner. Lastly, CIP itself can be used to propogate false   information.5.1 Secure Indexing   CIP is designed to index all kinds of data. Some of this data might   be considered valuable, proprietary, or even highly sensitive by the   data maintainer. Take, for example, a human resources database.   Certain bits of data, in moderation, can be very helpful for a   company to make public. However, the database in its entirety is a   very valuable asset, which the company must protect. Much experience   has been gained in the directory service community over the years as   to how best to walk this fine line between completely revealing the   database and making useful pieces of it available. There are also   legal considerations regarding what data can be collected and shared.   Another example where security becomes a problem is for a data   publisher who'd like to participate in a CIP mesh. The data that   publisher creates and manages is the prime asset of the company.   There is a financial incentive to participate in a CIP mesh, since   exporting indices of the data will make it more likely that people   will search your database. (Making profit off of the search activity   is left as an exercise to the entrepreneur.) Once again, the index   must be designed carefully to protect the database while providing a   useful synopsis of the data.   One of the basic premises of CIP is that data providers will be   willing to provide indices of their data to peer indexing servers.   Unless they are carefully constructed, these indices could constitute   a threat to the security of the database. Thus, security of the data   must be a prime consideration when developing a new index object   type. The risk of reverse engineering a database based only on the   index exported from it must be kept to a level consistent with the   value of the data and the need for fine-grained indexing.   Lastly, mesh organizers should be aware that the insertion of false   data into a mesh can be used as part of an attack. Depending on the   type of mesh and aggregation algorithms, an index can selectivly   prune parts of a mesh. Also, since CIP is used to discoverAllen & Mealling            Standards Track                    [Page 14]

RFC 2651                  The CIP Architecture               August 1999   information, it will be the target for the advertisement of false   information. CIP does not provide a method for trusting the data that   it contains.Acknowledgments   Thanks to the many helpful members of the FIND working group for   discussions leading to this specification.   Specific acknowledgment is given to Jeff Allen formerly of Bunyip   Information Systems. His original version of these documents helped   enormously in crystallizing the debate and consensus. Most of the   actual text in this document was originally authored by Jeff.  Jeff   is no longer involved with the FIND Working Group or with editing   this document. His authorship is preserved by a specific decision of   the current editor.Authors' Addresses   Jeff R. Allen   246 Hawthorne St.   Palo Alto, CA 94301   EMail: jeff.allen@acm.org   Michael Mealling   Network Solutions, Inc.   505 Huntmar Park Drive   Herndon, VA 22070   Phone: (703) 742-0400   EMail: michael.mealling@RWhois.netAllen & Mealling            Standards Track                    [Page 15]

RFC 2651                  The CIP Architecture               August 1999References   [RFC1913]       Weider, C., Fullton, J. and S. Spero, "Architecture                   of the Whois++Index Service",RFC 1913, February                   1996.   [RFC1914]       Faltstrom, P., Schoultz, R. and C. Weider, "How to                   Interact with a Whois++ Mesh",RFC 1914, February                   1996.   [CIP-MIME]      Allen, J. and  M. Mealling, "MIME Object Definitions                   for the Common Indexing Protocol (CIP)",RFC 2652,                   August 1999.   [CIP-TRANSPORT] Allen, J. and  P. Leach, "CIP Transport Protocols",RFC 2653, August 1999.Allen & Mealling            Standards Track                    [Page 16]

RFC 2651                  The CIP Architecture               August 1999Appendix A: Glossary   application domain:  A problem domain to which CIP is applied which      has indexing requirements which are not subsumed by any existing      problem domain. Separate application domains require separate      index object specifications, and potentially separate CIP meshes.      See index object specification.   centroid:  An index object type used with Whois++. In CIP versions      before version 3, the index was not extensible, and could only      take the form of a centroid. A centroid is a list of (template      name, attribute name, token) tuples with duplicate removed.   dataset:  A collection of data (real or virtual) over which an index      is created. When a CIP server aggregates two or more indices, the      resultant index represents the index from a "virtual dataset",      spanning the previous two datasets.   Dataset Identifier:  An identifier chosen from any part of the      ISO/CCITT OID space which uniquely identifies a given dataset      among all datasets indexed by CIP.   DSI:  See Dataset Identifier.   DSI-description:  A human readable string optionally carried along      with DSI's to make them more user-friendly. See dataset      Identifier.   index:  A summary or compressed form of a body of data. Examples      include a unique list of words, a codified full text analysis, a      set of keywords, etc.   index object:  The embodiment of the indices passed by CIP. An index      object consists of some control attributes and an opaque payload.   index object specification:  A document describing an index object      type for use with the CIP system described in this document. See      index object and payload.   index pushing:  The act of presenting, unsolicited, an index to a      peer CIP server.   MIME:  see Multipurpose Internet Mail ExtensionsAllen & Mealling            Standards Track                    [Page 17]

RFC 2651                  The CIP Architecture               August 1999   Multipurpose Internet Mail Extensions:  A set of rules for encoding      Internet Mail messages that gives them richer structure. CIP uses      MIME rules to simplify object encoding issues. MIME is specified      inRFC-1521 andRFC-1522.   payload:  The application domain specific indexing information stored      inside an index object. The format of the payload is specified      externally to this document, and depends on the type of the      containing index object.   polled server:  A CIP server which receives a request to generate and      pass an index to a peer server.   polling server:  A CIP server which generates a request to a peer      server for its index.   referral chain:  The set of referrals generated by the process of      routing a query. See query routing.   query routing:  Based on reference to indexing information,      redirecting and replicating queries through a distributed database      system towards the servers holding the actual results.Allen & Mealling            Standards Track                    [Page 18]

RFC 2651                  The CIP Architecture               August 19996.  Full Copyright Statement   Copyright (C) The Internet Society (1999).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Allen & Mealling            Standards Track                    [Page 19]