Sunday, December 10, 2006

IBM Mainframe databases

The most commonly desired database is DB2, which first appeared around 1983. I recall a telephone interview in 2002 in which I was asked about "indexable predicates" and to give circumstances where a full outer join would be used.

The next most common is IMS with the DL1 command language, the world of PCBs and PSBs. Sometimes IMS-DC is needed as a TP monitor, as it is a rare skill, since most people learned CICS only, and since relatively few installations still have it.

A simpler "relational" system was ADR Datacomm DB along with Datacom DC, which Chilton Credit Reporting in Dallas used in the 1980s (before takeover by TRW, eventually leading to a spinoff as Experian). It worked essentially as an inverted list. It did not make one very marketable for the job market entering the 1990s.

IDMS is a "network" system, originating with Cullinane and then belonging to Computer Associates from the 1990s. It had a fourth generation online language called ADS(O) which supplanted the need for conventional command level CICS programming. IDMS could work with files in VSAM format as well as its own proprietary format.(By the way, you can do command level CICS in Assembler was well as COBOL, but Macro level CICS was usually only in Assembler).

Sperry Univac (in the 1970s) had a DBMS similar to IDMS, called DMS-1100.

Another common database used to be ADABAS, with the accompanying 4GL NATURAL.

For life insurance and annuities, VANTAGE developed a proprietary system to access either VSAM files or DB2 with such specific structures that it is practically a DBMS on its own right, with very specific call structures and link deck conventions, that often require gurus to maintain.

No comments: