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rfc:rfc144

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]

Shoshani [Page 6]

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