Example: Describe a logical file using DDS

This example shows how to describe a logical file using DDS.

The DDS for a logical file, shown in the next example, must be in the following order:

1: File-level entries (optional). In this example, the UNIQUE keyword indicates that for this file the key value for each record must be unique; no duplicate key values are allowed.

For each record format:

2: Record format level entries. In this example, the record format name, the associated physical file, and an optional text description are specified.
3: Field-level entries (optional). In this example, each field name used in the record format is specified.
4: Key field level entries (optional). In this example, the Order field is used as a key field.
5: Select/omit field level entries (optional). In this example, all records whose Opnsts field contains a value of N are omitted from the file's access path. That is, programs reading records from this file will never see a record whose OPNSTS field contains an N value.
6: Comment.

|...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....8
     A* ORDER HEADER FILE (ORDHDRP)
     A   6
     A                                 1  UNIQUE
     A     2  R ORDHDR                    PFILE(ORDHDRP)
     A       3  ORDER                     TEXT('Order number')
     A            CUST                      TEXT('Customer number')
     A            .
     A            .
     A            .
     A     4  K ORDER
     A          O OPNSTS              5   CMP(EQ 'N')
     A          S                           ALL

A logical file must be created after all physical files on which it is based are created. The PFILE keyword in the previous example is used to specify the physical file or files on which the logical file is based.

Record formats in a logical file can be:

A new record format based on fields from a physical file
The same record format as in a previously described physical or logical file.

Fields in the logical file record format must either appear in the record format of at least one of the physical files or be derived from the fields of the physical files on which the logical file is based.