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