Views on issues relevant to data sharing on computer networks

Network Working, Group                                P.M. Karp, MITRE
Request for Comments #146                             D.B. McKay, IBM
NIC 6742                                              D.C. Wood, MITRE
                                                      12 May 1971

Categories: D.4, D.7
Obsoletes: none
Updates: none


                Views on Issues Relevant to Data Sharing
                          on Computer Networks


Introduction

The formation of a committee to address the problems of achieving
data sharing on the ARPA Network, as suggested by Arie Shoshani
(RFC #140) is desirable at this point of network development.  We
concur with Shoshani's ideas (presented in an introductory paper
to the network data sharing meeting, scheduled for Tuesday, May 18)
and believe that purpose of the committee should be -

        a) to classify the issues involved and to propose various
           approaches;

        b) to integrate the hitherto independent network activities
           that address problems in the area of data sharing, and;

        c) to set up and coordinate appropriate experiments to test
           the services developed and to evaluate alternative
           approaches.

This position paper is intended to augment Shoshani's as a basis
for discussion at the data sharing meeting. No attempt is made
to discuss specific means of implementation since many approaches
to data handling problems are possible and have been proposed.
Rather, our viewpoint on what the committee's role should be in
giving some cohesion to various existing implementations is
presented.

Our Views

    One approach to achieving data sharing on the ARPA Network can
be thought of as having three stages, which roughly correspond to
the modes of use or operation. Within each stage are various levels
of development required to get to the next stage. This development
is not necessarily sequential. A description of the three stages
follows.

Stage 1: Data handling services are provided at various Hosts.
         The user talks directly to the serving Host (via TELNET
         or by addressing a known socket) to explicitly access
         the service.  This mode of operation corresponds to
         Bhushan's category of "direct" usage (RFC #114).  The
         data services provided by the serving Host range from
         simple ones, such as White's file transfer system (RFC #122)
         to sophisticated systems such as the CCA's data machine
         (NIC 5791 and 6706).

Stage 2: The user has access to an intermediate process or data
         control facility* that routes his requests for a particular
         data service to the serving system. The user must explicitly
         identify the data services to the used.  This mode of
         operation corresponds to Bhushan's category of "indirect"
         access. The data control facility provides the necessary
         control commands, data transformations, and accessing
         methods. A single request would include the use of several
         interacting services. For example, Heafner's Data
         Reconfiguration Service (RFC #l38) could be used in
         conjunction with the use of CCA's data machine.






_______________
*The data control facility is not necessarily located at his local
Host. Such a facility may exist on from one to all Host (i.e.,
ranging from centralized to completely distributed).

Stage 3: The user treats the network as a single resource and is
         unconcerned with the location of the services, data files,
         etc. All references are by name. In this mode of opera-
         tion, the data control facility can function as a referral
         center for data service requests by using the most ap-
         propriate data service available and by automatically
         combining the use of several services that may be needed
         to satisfy a request.  For example, data could be retrieved
         from several files, each managed by a different data
         management system. The data control facility must be
         cognizant of the location of data files, their structure,
         data management system capabilities, etc.

Some approaches to the design of the data control facility have
been suggested by Shoshani, notably the integrated data management
system (IDMS) and the unified data management system (UDMS). The
notion of the network machine (RFC #51) is closest to the capabilities
one would see in Stage 3.

Relevant Areas of Development

The data control facility can range anywhere from a simple inter-
face to an intelligent front-end processor to a network-wide re-
ferral system.  In any case, a common means is desirable for
handling applications such as file transfer, on-line update and
retrieval of data, information gathering and reporting, and program
access to data. To attain this end, a few of the areas in which
developments will be required include:

     a)  a data description language, permitting the user to define
         the physical structure of files, to define logical files,
         and to categorize data fields for name referencing. The
         language should be designed to facilitate the resolution of
         physical discrepancies in data and file structures. The
         user should be able to superimpose logical restructuring of
         data without any change in the physical structure.

b) a control or access language that can be mapped into
         various data management languages. Considered here is
         Shoshani's suggested two-level approach with perhaps a
         meta-language implementation to facilitate conversions
         among already existing languages.

     c)  methods for managing and merging distributed data, search
         mechanisms for file directories, error recovery techniques,
         etc.

Independent ARPA Network activities that in effect constitute
Stage 1 have touched on these areas and should be incorporated into
the overall data sharing scheme such that all of the isolated
pieces are compatible.  For example,

      a) the data reconfiguration service (RFC #138) would be
invoked by the data control facility whenever data transformations
are required.

      b) the file transfer protocol (RFC #114, #122)
should be consistent with other data handling services.

      c) CCA's data machine should be a subset or part of any data
control facility. The network data language and set of data
management services that they plan to implement can perhaps be
adopted network-wide.

      d) the network machine concept (RFC #51) for defining the pro-
gram and data environments should be resurrected. The data control
facility should be a subset of a network machine architecture.

Some other relevant topics include NIL (RFC #51), DEL (RFC 5), the
notion Of MYLOCAL n, YOUR LOCAL n, and STANDARD n (RFC #42), user
level protocol objectives as described in RFC #76 and #91.

Experimentation and Testing
---------------------------

As data services are developed on the network, a coordinated
effort is desirable

     a)  to exercise individual implementations to see
         if they work, both alone and in conjunction with
         other data services, and

     b)  to evaluate alternative approaches.

Some examples of experimentation to test data services follow:

     1.  File Transfer Protocol

         The file transfer protocol should be used to
         manipulate data files controlled by various
         systems.

     2.  Data Transfer to Data Computer

         The ability to transfer existing data bases and
         their structures onto the data computer should be
         demonstrated.

     3.  Data Restructuring

         The ability to define logical restructuring of
         data for users needs which would be accessible by
         name should be demonstrated. The original physical
         structure would be maintained.

     4.  Data Transformation

         The ability to access various data management
         systems on the network without the user being
         concerned with the data transformation involved
         should be demonstrated. Necessary calls to forms
         available on the Data Reconfiguration Service
         should be handled automatically and should be
         transparent to the user.

5.  Data Consistency

         Problems of maintaining consistency when duplicate
         copies of a data file exist and updates to the file
         are made should be investigated. Automatic use of
         file transfer protocol and DRS to generate new
         duplicate copies should be included.

     6.  Data Privacy

         Access controls for privacy Of data files in the
         network environment should be designed and evaluated.
         This includes controls on parts of distributed files.

Our recommendation is that the committee on data sharing be
responsible for coordinating development in these areas, for
attempting to maintain consistency among data services, and for
testing services in a series of experiments as they are implemented.





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