Mapping instructions determine which source records are used for data in tables on the target database and designate the source for the data in each table. Data can be acquired from the legacy database, or can be initialized with constant values. Mapper works from the database definitions provided by schema extracts and builds a migration definition file for the Translator based on relationships defined by the analyst. Some database types are written to flat files using an unload program generated by a Schema Extract routine. Other types can be moved directly to the target system.
Unload files form the remaining input for the Translator.
The first phase of the Translator verifies the mapping definitions compatibility of data structures, and examines syntactical accuracy. The second phase builds indexes for internal use during migration. These indexes improve performance during the creation of the target database files. They also provide the reference capability for accessing other database records. The third phase reads the legacy data files, applies the instructions established during mapping, and produces a set of files in the proper format for populating the target relational database.