Generally, data reengineering achieves a very simple objective: it enhances the value of the data in DB2® and therefore its value to your business. In some ways it is analogous to the data transformation that often occurs when you extract data from your operational databases into a data warehouse.
Prior to migrating a VSAM file, you should consider how you plan to use the data in DB2 in order to determine the required level of reengineering. For simple files, you may be able to achieve your required level of data reengineering using the facilities built into to CICS® VT. These are activated as a result of the mapping process. For other files, you may have to write user exits.
You should also consider the effort that you are prepared to invest in the conversion. If you want to convert as quickly as possible to improve online availability, and you are not concerned about the initial DB2 design, the automated migration facility should meet your needs. This facility provides a degree of user-driven field level reengineering, but does not support record-level reengineering. When DB2 design is important, a combination of the manual mapping method and user exits will be required in many cases.
You can potentially migrate a data set more than once. Initially, you might decide to migrate with minimal or no reengineering, then at some stage in the future migrate it again with more complex reengineering. This can often happen with some of the files that you migrate early in your migration project. As you gain more experience and knowledge of CICS VT, you realize that data sets you migrated previously could provide more business benefit if more reengineering occurs. CICS VT lets you migrate to a new DB2 design at any time.
Reengineering is not just for improving the value of your data. You can use it for data validation, and potentially eliminate data exceptions that you might be experiencing currently with your VSAM application files.