LANGUAGE REQUIREMENTS FOR UNDERSTANDING RETRIEVED DATA
Fred C. Billingsley
Jet Propulsion Laboratory
California Institute of Technology
Pasadena, California, USA
INTRODUCTION
A primary focus of information systems activities is to provide the
techniques and tools to enable data users to locate, acquire, and utilize
data in the continuing search for understanding. This requires the
interfacing of multiple data centers and data archives in order to provide
access to their information sets and supporting tools and services.
The standardization being planned and implemented for space information
systems stresses interoperability - the attempt to make the interfacing
"seamless". When there is a requirement to obtain information from another
location or an archive, there is a parallel need to transmit a complete
description. This description is the function of a Data Interchange
Language (DIL). The DIL should be powerful enough to enable parsing of the
transported information, whether transported via electronic or recorded
media. The ultimate objective is to minimize the need for manual inter
vention in the transfer process.
The objective of this overview is to describe the method of facilitating
this transfer between dissimilar computers, using the Transfer Syntax
Description Notation (TSDN). This notation is being developed as a generic
capability to allow transfer of discipline-dependent information in a
discipline-independent and medium-independent manner.
THE GENERAL DATA MODEL
"Data" is a broad term. It has been convenient to divide the concept into
smaller parts, so they may be considered separately. This has historically
been done in the industry using the terms Volume, File, Record, Elements or
Data Fields, byte, bit, representing progressively smaller entities. These
are usually considered as nested.
We will continue to use these terms where appropriate. We also expect to
make maximum use of available commercial capabilities to avoid the need of
inventing the computer industry over again. Specifically, and for example,
we will use the conventional definitions for byte (or Octet), and bit. We
also expect to find useful the industry concepts of, and services relating
to, records and files.
The TSDN has been developed with a logical model of organization of the
data it is describing as:
Volume
File
Record
Data Field
+( Files )
::= +( Records )
::= +( Data Fields )
::= Compound | Simple
