You define a subfield by specifying blanks in the Definition-Type entry (positions 24 through 25) of a definition specification. The subfield definition(s) must immediately follow the data structure definition. The subfield definitions end when a definition specification with a non-blank Definition-Type entry is encountered, or when a different specification type is encountered.
The name of the subfield is entered in positions 7 through 21. To improve readability of your source, you may want to indent the subfield names to show visually that they are subfields.
If the data structure is defined with the QUALIFIED keyword, the subfield names can be the same as other names within your program. The subfield names will be qualified by the owning data structure when they are used.
You can also define a subfield like an existing item using the LIKE keyword. When defined in this way, the subfield receives the length and data type of the item on which it is based. Similarly, you can use the LIKEDS keyword to define an entire data structure like an existing item. See Figure 131 for an example using the LIKE keyword.
The keyword LIKEDS is allowed on any subfield definition. When specified, the subfield is defined to be a data structure, with its own set of subfields. If data structure DS has subfield S1 which is defined like a data structure with a subfield S2, a programmer must refer to S2 using the expression DS.S1.S2.
You can overlay the storage of a previously defined subfield with that of another subfield using the OVERLAY keyword. The keyword is specified on the later subfield definition. See Figure 57 for an example using the OVERLAY keyword.
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