File Management and the Data Dictionary
Some of the file management facility is system- or platform-specific, while application design is system-independent. From the integration of the two facilities, you can develop an APPX application without regard to the target platform, yet operate the application to take maximum advantage of the system it operates on.
The file management facility is most tightly integrated with those dictionary components that are database-dependent. The term database-dependent, or database-related, refers to what is unique to a specific database (as defined by file management).
In the APPX dictionary, permanent disk-based files are database-dependent. Each database that accesses a permanent, disk-based file actually accesses a separate copy of the file. Unstored files, temporary files, work fields, and memory files aredatabase-independent. In this case, APPX maintains a single file that is accessed by all databases.
For database-dependent files, a number of dictionary specifications provide information and defaults for, or impose restrictions on, the file creation utility in file management. These specifications include File Name, Organization, Variable Length?, Compress Records?, and Create by File Management? For disk-based temporary files (database-independent), file management refers to the dictionary specifications for file size information.
The dictionary is also integrated with file management's restructure utility. APPX uses this utility to automatically restructure files to reflect such changes as the length of a field or a change in storage type. The flag that indicates a file requires restructuring is maintained by the data dictionary when it is compiled or recompiled. Refer to the System Management Manual for a discussion of the restructure utility.
|