Monday, 22 October 2007

IMS at 40

With the recent announcement of Version 10 of IMS, I thought it would be quite interesting to take look at what IMS actually is, before seeing what’s in the new version.

Information Management System, to give it its full name, is a combination of database and transaction processing system. I’m not sure whether it’s 40th birthday was last year or next year because work started on it back in 1966, but it was 1968 when it was first running anywhere.

There are three databases associated with IMS DB. These are called “full function”, “fast path”, and High-Availability Large Databases (HALDBs). With full function databases – the original database type – data is stored in VSAM or OSAM files and can be accessed using HDAM, HIDAM, HSAM, HISAM, and SHISAM access methods. Full-function databases are derived from DL/I databases that were around at the time (1966). There are two types of fast path database – Data Entry DataBases (DEDBs) and Main Storage DataBases (MSDBs). These databases do not have indexes and are stored in VSAM files. HALDBs are the newest (since V7). They are like souped-up very big full-function databases.

IMS TM (sometimes written as IMS DC – Data Communications) provides a way for users to run transactions to get information from the database. It is perhaps most like CICS in the way it allows users to work. IMS stores transactions in message queues and then schedules them to run. Like CICS there is a lot of work going on internally to maintain the integrity of the data and the transaction.

Highlights of the V10 announcement include enhanced IMS/XML database support, enhanced XML and Web services capabilities, more autonomic computing, and improved performance in database utilities. Of course, full details are on the IBM Web site at

IMS is reckoned to be installed in 95 percent of Fortune 1000 companies, which makes it an important piece of software. It might have been around for quite a while, but by embracing SOA and Web services it has ensured that it will be with us for a long time yet.


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A Anand said...

Very informative blog. IBM has tried to keep pace with SOA revolution. IBM's IMS SOAP Gateway integrates IMS assets in a SOA environment.