Describing database files using DDS

 

When you describe a database file using data description specifications (DDS), you can describe the file at the file, record-format, join, field, key-field, and select/omit-field levels.

• File-level DDS provides the system information about the entire file. For example, you can specify whether all the key field values in the file must be unique.

• Record format-level DDS provides the system information about a specific record format in the file. For example, when you describe a logical file record format, you can specify the physical file that it is based on.

• Join-level DDS provides the system information about the physical files that are used in a join logical file. For example, you can specify how to join two physical files.

• Field-level DDS provides the system information about individual fields in the record format. For example, you can specify the name and attributes of each field.

• Key field-level DDS provides the system information about the key fields for the file. For example, you can specify which fields in the record format are to be used as key fields.

• Select/omit field-level DDS provides the system information about which records are to be returned to the program during file processing. Select/omit specifications apply to logical files only.

• Example: Describing a physical file using DDS
  This example shows how to describe a physical file using DDS.

• Example: Describing a logical file using DDS
  This example shows how to describe a logical file using DDS.

• Additional DDS field definition functions
  You can describe additional information about the fields in the physical and logical file record formats with function keywords (positions 45 through 80 on the DDS form).

• Using existing field descriptions and field reference files to describe a database file
  If you want to use a field description in an existing file, you can copy that field description into your new file description. You can also create a field reference file to contain the field descriptions that you need for any group of files.

• Using a data dictionary for field reference in a database file
  You can use a data dictionary and the interactive data description utility (IDDU) as an alternative to using a DDS field reference file. IDDU allows you to define fields in a data dictionary.

• Sharing existing record format descriptions in a database file
  A record format can be described once in either a physical or a logical file (except a join logical file) and can be used by many files. When you describe a new file, you can specify that the record format of an existing file is to be used by the new file.

 

Parent topic:

Describing database files

 

Related concepts

DDS for physical and logical files