CoreData42 min
IMS database and transactions
IMS is IBM's hierarchical database and transaction manager, still running core systems at many banks, insurers and governments. Learn how its data is shaped, how COBOL programs read and update it with DL/I calls, and how IMS is operated.
What you will be able to do
- Explain the two halves of IMS (IMS DB and IMS TM) and the region types programs run in
- Read a hierarchical database structure: segments, parents, children, twins and hierarchical sequence
- Understand how DBDs and PSBs control what a program can see, and write the common DL/I calls in COBOL
- Interpret the most common status codes and the basics of IMS operations and recovery
Lessons
- What IMS is and where it runsIMS has two parts: IMS DB, a database that stores data as trees rather than tables, and IMS TM, a transaction manager that queues and runs online transactions. Many sites use…
- Hierarchical data: segments, DBDs and PSBsAn IMS database is a tree. Each record starts with a root segment, with child segments hanging beneath it. The DBD describes the tree; a PSB describes which parts a particular…
- DL/I calls from COBOLA COBOL program talks to IMS by calling CBLTDLI with a function code, a PCB, an I/O area and optional segment search arguments (SSAs). After every call it checks the…
- IMS in productionIMS is operated with slash commands to display and control transactions, programs and databases. Recovery depends on image copies and logs recorded by DBRC.
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