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Format Description - The TSDN 
The philosophy behind the TSDN construction is that a data transmission 
consists of a series of bytes. These bytes have no inherent meaning nor 
interrelationships, requiring that everything be defined. The user may 
define keywords (Labels) for the data fields of the user modules. These 
fields may be described and retrieved by using the labels as keywords. 
These definitions are carried in a series of statements, or SEGMENTS. This 
convention defines the use of these descriptive Segments to describe the 
structure of a file and each data record in the file. 
Each TSDN segment has the same basic structure: 
Segment Tag Tag Delimiter Segment Value Segment Delimiter 
The structure of the segment value field varies, depending on the use of 
the segment. 
The TSDN may be described as Keyword-driven, where the TSDN keywords are 
segment tags. This allows the building of a TSDN Module from a relatively 
small group of specification-defined segments plus user-defined segments. 
This approach allows a standard, recognizable, group of segment tags to be 
specified for the TSDN, from which a given instance may be assembled. Only 
those segments needed in a given instance need be used. 
Data objects may be simple (primitive or compound) or aggregate (file, 
record, structure). There are only three fundamental data types, from 
which others may be constructed: 
Primitive - named, undivided 
Compound - named, a sequence of unnamed components 
Aggregate - named, components named individually, with relationships. 
Only one TSDN segment type (OBJECT) is required to describe all aggregate 
objects, at whatever aggregation level. An OBJECT segment is used to 
describe the logical structure of each aggregate object, while a TYPE 
segment is used to describe the concrete syntax (format) of each primitive 
or compound data field. Other segments are defined for use in describing 
other aspects of the data. 
An Example 
Let us take as an example, the personnel record illustrated in Appendix E 
of ISO 8824 (ASN.l). 
Name: 
Title: 
Employee Number: 
Date of Hire: 
Name of Spouse: 
Number of Children: 
John P Smith 
Director 
51 
17 September 1971 
Mary T Smith 
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