Knowledge of IMS database systems is increasingly fading in businesses with time. Hierarchical IMS databases required more maintenance and, in comparison to similar database systems, accessing data is very difficult. As a result of high maintenance and license costs, IMS database systems are very costly. As a result, many clients consider replacing IMS with DB2 or Oracle, be it on the mainframe or a decentralized system, as part of a rehosting project.

Through the integration of an access layer, the logic of the application program is not changed. Access to DB2 or Oracle is straightforward for old application programs via SQL using a data handler. Changes to the application program are restricted to exchanging the existing call interface. This minimizes time and cost spent on the project.

The available IMS database segments are transferred into a DB2 model with the help of tools. This ensures the continued hierarchical relationship of the segments. From the available, PSB, DBD, and copy segment information the corresponding database definitions are automatically generated for the respective target database system. These can then be modified according to individual requirements.

In order to transfer data from IMS to DB2 or Oracle the data must be read from the IMS while observing the hierarchical model. This occurs using special unload or load programs generated on the basis of the identified data definitions. The data are then automatically transferred to the target system.

Using an access layer, the application programs basically remain unchanged. Adjustment boils down to a purely technical modification of the call interface. This reduces both the cost of changes and also the necessary technical and functional tests. Furthermore, the project risk decreases significantly, as the number of potential error sources is minimized.

IMS is licensed by IBM as MLC (Monthly License Charge) and is a significant cost factor. These licensing costs, and possible further IMS-specific maintenance costs, can be saved as a result of this migration.

The application programs maintain their functional logic. The programs do not become any more complex and, therefore, can be managed and further developed by the same employees.