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Network Working Group                                        A. ShoshaniRequest for Comments: 144                                            SDCNIC: 6729                                                  30 April 1971Data Sharing on Computer Networks   The enclosed is an introductory paper for the meeting which will be   held in Atlantic City as part of the ARPA Network meetings.  The   schedule for the meeting will be published soon by Steve Crocker.   The Agenda of the meeting will include:      a.  Presentation of the introductory paper.      b.  Open discussion to exchange comments and ideas.      c.  Attempt some recommendations.      d.  Possibly set up a committee of interested people.   If you have interest in the subject please plan to attend.INTRODUCTION   One of the benefits expected from the use of Computer Networks is the   sharing of data among users of the system.  This paper is an attempt   to classify the issues involved, discuss some approaches that might   be taken to achieve the goal of facilitating data sharing and to   point out some advantages and disadvantages of these approaches.CONSIDERATIONS   In the process of selecting an approach one has to consider the   following issues:      1. Does the approach provide the use of one language to access all         data on the network?      2. Does the approach facilitate sharing of existing data created         and manipulated by existing data management systems?      3. Does the approach encourage users to share data and use the         facility provided?  How evolutionary is the approach?      4. Could a failure of one node in the network cause the failure of         the data sharing facility?      5. Does the approach promote or hinder further development of data         management systems?Shoshani                                                        [Page 1]

RFC 144            Data Sharing on Computer Networks       30 April 1971      6. What are the implementation considerations?      7.  What are speed considerations?POSSIBLE APPROACHES      1. Centralized data management system (CDMS).         This approach is consistent with the idea that a Computer         Network eventually will evolve into a collection of specialized         service nodes, where each node would perform a specific         function well.  Users will use services on nodes according to         their needs.  For example, one node could be a PL/I machine         (possibly a microprogrammed machine to perform PL/I compilation         efficiently), another node could be a "number cruncher" for         parallel-structured problems (ILLIAC IV), etc.  In the same way         there will be a node responsible for all data management needs         for the network.         Depending on the assumptions made one of two ways can be         chosen:         a. As assumption that we must be able to share all data,            implies that the same data management system can create and            manipulate this data, and therefore must perform all the            functions required of a data management system, regardless            of the particular use.  It is generally agreed that such a            task is monumental and impractical (if not impossible),            since different data management systems are designed to            perform specific functions well on the expense of degraded            performance of other functions (e.g., fast retrieval of            large files, limited updating capabilities).         b. The assumption is made that users will share only data from            the same file on a particular data management system.  In            this case one can implement different data management            services for different tasks, but put them all on the same            node to provide a data management service to the Network            users.  This approach can still use one common language to            access these services.  This is apparently the approach            taken by CCA as indicated in NIC memo 5791.      2. Standardized data management system (SDMS).         In this approach a particular data management system is adopted         to be implemented on all nodes.  This provides for a         standardized data management language as well as an identical         logical data structures.  Alternatively, one can choose a setShoshani                                                        [Page 2]

RFC 144            Data Sharing on Computer Networks       30 April 1971         of data management systems to be implemented on all nodes, then         be able to share information manipulated by the same data         management system on different nodes.  This approach has many         drawbacks as will be discussed later.      3. Integrated data management system (IDMS).         This approach suggests the integration of local (to the node)         data management systems and local data (files) through the use         of appropriate interfaces and a common data management         language.         Under this category there may be different approaches depending         on the function of the interfaces:         a. There is an interface module in every node for every local            data management system.  The interface performs a dual            function:  on the way out--it issues requests in the common            language to remote nodes; on the way in--when a request in            the common language is received, the interface performs            translation from the common language to the local data            management language.  From a single request the translation            might produce a series of commands in the local language            (for example, suppose that the local language permits the            specification of one quantifier only, such as "age<_41."            Suppose that the request received in the common language            specifies "list all names where age<_41 and children _>5."            The translation will produce a series of commands of the            form:  "list all names where age <_41," "save the list            temporarily," "list all names in temporary file where            children>_5").         b. Move all local interfaces which were described above into            one central node.  This node is now the service node.  It            accepts a request in the common language and produces a            series of commands to all nodes involved, in their local            data management languages.         c. The local interface accepts the name of a local file (or            relevant portion of the file), and sends this file to the            requester after performing a translation of the data.  The            data can be translated using a technique such as the "Form            Machine" (described in NIC 5772).  The file is translated            from the local data management data structure to the            requesters data structure, so that the requester can perform            the desired function using his local data management system.Shoshani                                                        [Page 3]

RFC 144            Data Sharing on Computer Networks       30 April 1971      4. Unified data management system (UDMS).         This approach suggest the use of a standard interface which is         to be part of every data management system on the Network.  The         interface has three ends.  One to the user language, one to the         particular physical system used and one to the Network.  The         interface should be global enough to permit separation of         system decisions from user language decisions.  If this         interface is standardized on a Network, it will facilitate         communication between local data management systems in a         unified way, while permitting the development and evolvement of         different local data management systems.  (This is a rough         description of the approach taken by Barry Wesseler in Utah.)THE COMMON LANGUAGE   It is well known that the design of a language involves a compromise   between the ease of use of the language and its capability to express   the functions desired.  A try to merge two languages usually results   in the worsening of one or both of these considerations.   For the purpose of having a common language for data management it   may be desirable to separate between the above mentioned   considerations.  Use natural-language for ease of use, and a formal   intermediate language powerful enough to express any functions   desired.  This is the approach taken in the development of CONVERSE   in SDC [1].  The intermediate language can be as complex as one likes   since it is invisible to the user.DISCUSSION   Predictions for future use of computers (and therefore computer   networks) point out that "in 1975 we will process mostly data" [2].   Therefore, the problem of sharing data on a computer Network, as well   as accessing data from remote nodes in some common language are   extremely important.   If all that is desired is the sharing of data in a file by more than   one user, then the CDMS approach is appropriate.  Approach la is   impractical, but lb can provide a valuable service.  Selecting this   approach does not permit the sharing existing data which was created   with existing data management system, unless a restructuring of the   data for the CDMS is performed.  This approach does not easily permit   the development of new data management systems since the CDMS should   stay stable for the Network use.  It does not involve translation of   data or languages and therefore should provide good access speed.Shoshani                                                        [Page 4]

RFC 144            Data Sharing on Computer Networks       30 April 1971   The SDMS approach has many drawbacks.  Selecting it implies the   imposition of a particular data management system on all nodes.  It   inhibits further development.  It does not permit the sharing of   existing information.  The main advantage would be the modularized   structure so that the failure of one node cannot cause the failure of   the entire system.  Also, because of the standardized approach   sharing of data from different nodes does not involve any   translation.   The main advantage of the IDMS approach is that it permits the   continued use of existing data management systems with existing data   bases associated with them while permitting the sharing of data among   the network community of users.  Since it permits the continued use   of local data management systems it is the most evolutionary approach   and most likely to be accepted by a user of an existing data   management system.  There are applications where users on each node   on the Network perform mostly local access of data, and less often   find it desirable to be able to share data with other nodes.  For   example, if hospitals are connected to nodes of a Computer Network,   then most of the data about patients is accessed locally, but   sometimes it is necessary to access information from other hospitals,   such as global statistical information.  The same situation exists   for criminal files, local branches of banks, credit bureaus,   warehouses, etc.  Approach 3a permits the advantages of   modularization, but 3b is easier to implement since no additional   interfaces are necessary in the different nodes.  Approach 3c seems   hard to implement and can introduce inefficiencies since it involves   translation from one data structure (which might be designed for   efficiency) to another data structure (which may not be as   sophisticated).  It also involves the shipment of large amounts of   data across the network.   The UDMS approach permits the continued development of local systems   while facilitating a unified way for Network communication of data   requests.  It is not clear at this point whether this approach is   practical.   Other important issues concerning sharing of data on a Computer   Network, and which are mentioned in [3] are overlap of information in   different files and the possibility of the same information to be   contradictory, security and privacy problems, sponsors of a file vs   users of a file, and others.Shoshani                                                        [Page 5]

RFC 144            Data Sharing on Computer Networks       30 April 1971ACKNOWLEDGMENT   Discussions with the following people were very valuable:  Al Vorhus,   Peggy Karp and others in MITRE, Barry Wesseler in Utah, Gerald   Levitt, N. Cohen and others in RAND, Clark Weissman, and Charlie   Kellogg in SDC, Richard Winter of CCA.REFERENCES   1. Kellogg, C. "A Natural Language Compiler for Online Data      Management." Fall Joint Computer Conference Proceedings, Vol. 33,      part I, 1968.  pp. 473-492   2. Clamons, Eric H. "Introductory Remarks to Data Base Management      Seminar." Proceedings of Workshop on Networks of Computers (NOC-      1969) NSA pp. 89-90   3. Hicken, George "Data Base Confrontation in an Information      Network." Proceedings of Workshop on Networks of Computers (NOC-      1969).  NSA pp. 99-115.         [ This RFC was put into machine readable form for entry ]             [ into the online RFC archives by Ryan Kato 6/01]Shoshani                                                        [Page 6]