During generation, EGL can generate data description specifications (DDS) information from EGL record definitions that are used for file I/O operations.
The DDS information generated by EGL is useful only to the iSeries system administrator or application developer. The system administrator can use the DDS source members, or modified versions of them, to create the files that do not already exist on the iSeries system. Using the DDS source information to create the files qualifies these files for iSeries data management functions, such as specifying key fields, unique keys, and logical files.
You are not required to use the DDS source information to create files because EGL does not require that the files an application accesses be externally described. EGL relies on the record definition, which is built into the *PGM object, for the structure of a record. However, using the DDS information guarantees agreement between the application's view of the record structure and the record data stored on the iSeries system.
Indexed and indexed alternate specification record organizations might require that you modify the corresponding DDS source member. Adding DDS keywords to the file- and record-level identifiers in the DDS source member is the minimum modification necessary. Table 3 shows the DDS keywords and the conditions under which they are required.
You can add other DDS keywords to optimize record retrieval and simplify
application logic. For example, logical files can be used to select a
subset of physical file records. You can also to build your own DDS
source member, based on your knowledge of the EGL record definitions in the
application. In this case, individual field names and field lengths in
the DDS source need not match those of the EGL record definition.
However, the record length and key field length of the EGL record definition
and the DDS source must be equal.
Table 3. Conditions for using DDS keywords
DDS keyword | Condition |
---|---|
PFILE(pfname) | When using the DDS information to create a logical file. pfname identifies the physical file on which the logical file is based. PFILE is a record-level keyword. |
UNIQUE | When the application tests for the unique or duplicate record I/O error conditions. UNIQUE is a file-level keyword. |
EGL supports simple logical files that use only one record format. The DDS source information specifies only one file on the PFILE keyword.
EGL creates DDS source members without specifying a member type. To assist you in modifying the DDS source information, change the member type to one of the following:
Changing the member type to PF or LF enables the Source Entry Utility (SEU) prompting to help you to modify the DDS source member.
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