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+Network Working Group                                        A. Shoshani
+Request for Comments: 144                                            SDC
+NIC: 6729                                                  30 April 1971
+
+
+                   Data 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 set
+
+
+
+Shoshani                                                        [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 1971
+
+
+ACKNOWLEDGMENT
+
+   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]
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+Shoshani                                                        [Page 6]
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