90
Compound Field
Simple Field
+( Compound I Simple )
Octetstring I Bitstring
The notation ::= means "is composed of"
+(.„) indicates "consists of one or more
I indicates alternate
Within any closed endeavor, several things are required to be defined for
each entity and aggregation:
An instance identification - its name.
How to recognize or bound it.
How to parse it - its format or syntax.
Relationships among its parts and to other entities.
As long as the endeavor is closed, these definitions are arbitrary, but all
of them must be stated, either directly or as analogs to terms used outside
of the endeavor. When the TSDN module is transferred or makes use of
commercial (i.e., outside) capabilities, these terms must be mapped into a
language understood by the outside facilities. "Record" needs a special
comment. A number of external systems and languages do not recognize the
concept of record. Therefore all references to "record" will mean logical
data record, and definitions are needed for use within the endeavor.
Particular care must be taken that the internal protocols do not interfere
with the external ones.
REQUIREMENTS AND ATTRIBUTES FOR A DIL
A number of requirements have been suggested for the data language (DIL) to
be used to write the description. Among them are:
Ability to be used either separated from or attached to the data file,
to describe already-standardized and fixed formats.
Ability to name and describe data primitives, including machine
binary, non octet-aligned binary fields, and the various character
mode numerical representations of ISO 6093.
Ability to name and describe commutated and other structured data.
Ability to describe logical relationships between data objects in a
record.
Ability to describe logical relationships between data records in a
file.
Ability to describe logical relationships between data files in a
volume.
Ability to reference data at various levels of abstraction.
In addition, there are several attributes necessary for acceptance:
Must be application-independent.
Must be medium-independent.
Must be machine-independent.
Must be conceptually simple and self-documenting.
Must be human readable after minimum training.
Must be usable
between diverse DBMSs;
