IBM Mainframe Forum

Hello guys,

Why companies still continuing usage of IMS-DB even after DB2 is launched?

What are the benefits of IMS over DB2?

Why companies still continuing usage of IMS-DB even after DB2 is launched?

One reason is that conversion from one database to another can be a risky and expensive proposition. IMS is a hierarchical database whereas DB2 is relational -- so the database structure has to be changed, in some cases significantly. Capturing the business logic in the conversion can be difficult since the programs are often quite old (and in some cases source may not be available any more). As long as the IMS system is working and stable, why take the risk of changing to DB2?

The continued use of IMS does not necessarily depend upon IMS having benefits over DB2. If it costs $3 million to convert from IMS to DB2, and the company gets nothing from the conversion except a functional DB2 system, where is the rationale for doing the conversion? They are not likely to save $3 million in costs by converting, even amortizing over many years. Plus they have the risks of breaking working business logic, extensive testing to ensure the DB2 system works the same as the system it is replacing, and the difficulty of finding someone to do the conversion.

Similar logic often applies to moving applications off the mainframe. A previous employer had an application (one single application) that was estimated to cost $7 to $10 million dollars to convert off the mainframe. The vendor stopped supporting the mainframe version, so the employer had to move off it; if the vendor had continued to support the mainframe it is doubtful that they would have spent the money for the conversion.