Writing a Navigational DML Program › Common Considerations › Including Data Descriptions

Including Data Descriptions

Descriptions of the following structures must be included in the program in order to reserve space for them in variable storage.

• IDMS Communications Block- CA IDMS uses the IDMS communications block to post status information back to the application program concerning requested database services. The description of the IDMS communications block is generated as a record named SUBSCHEMA-CTRL (in COBOL) and is often referred to as the subschema control block.
• Subschema Names (COBOL only)- COBOL programs require the generation of a name literal for the subschema, and each record, set, and area included in the subschema.
• Subschema Records- The description of each database record to be accessed by the program must be included. Only records contained in the subschema may be accessed and the generated description reflects the subschema's view of the record rather than that of the schema.

The programmer controls how and where the data descriptions are generated using precompiler-directive statements. For example, the COBOL programmer can automatically generate all required descriptors at the end of the WORKING-STORAGE section by extending the PROTOCOL statement as follows:

IDMS-CONTROL SECTION.
PROTOCOL MODE IS BATCH DEBUG
         IDMS-RECORDS WITHIN WORKING-STORAGE.

Alternatively, the COBOL programmer can generate the descriptions at the end of the LINKAGE SECTION by specifying:

IDMS-RECORDS WITHIN LINKAGE.

To have complete control over where structure descriptions are generated, the COBOL programmer can specify:

IDMS-RECORDS MANUAL.

The programmer then inserts a COPY statement, as shown below, at the point where the descriptions are to be generated:

COPY IDMS SUBSCHEMA-DESCRIPTION.

Additional forms of the COPY IDMS statement permit COBOL programmers to generate descriptions for the IDMS communications block, subschema names and subschema records separately, and control the level numbers that are generated.

See Copying Record Definitions and Their Synonyms for more information on copying information from IDD.