The IBM IMS and its working method
The IBM IMS (Information Management System) is a joint hierarchical database and transaction management software which was first introduced to power the Apollo Space Program. It was designed by IBM with the help of Rockwell and Caterpillar in 1966 for keeping a track of the bill of material in the Saturn V moon rocket and other space vehicles. Because of its security, reliability and performance, the IMS is considered as the backbone for a huge chunk of the world’s cumulative data. In fact, almost all the Fortune 1000 companies use this management system and over fifty billion transactions are stored and computed through its databases per day! Vern Watts was the chief architect of IMS and continued to be so until his death in 2009.With its ever increasing market, the IMS is considered as the highest revenue producing software product ever manufactured by IBM.
The IMS (DB1) model is a hierarchical one rather than the new relational database DB2 and is implemented using blocks of data called segments. Each of these segments can either be a root segment or a child segment with fields associated with them for storing information like name, age, phone number etc. Segments can be attached to another segments like a tree structure and thus constitute the underlying hierarchy of the whole model. A segment can be defined in terms of its size and also its privacy settings for security. There are three basic forms of IMS hierarchical databases:-
Full Function Database
It has primary and secondary indices accessed during DL/I calls from application programs like SQL calls to DB2 and was designed on the basis of DL/I which was used for Apollo. Some of its access methods are Hierarchical Direct (HDAM), Hierarchical Indirect (HIDAM), Simple Hierarchical Indexed Sequential (SHISAM), Hierarchical Sequential (HSAM) and Hierarchical Indexed Sequential (HISAM). Databases store data using the Overflow Sequential (OSAM) or VSAM method but OSAM benefits from the sequential access of IMS databases and perform better.
Fast Path Database
Data Entry Databases (DEDB) and Main Storage Databases (MSDB) are the two types of fast path databases and are suitable even for very high transaction rates. Virtual Storage DEDB’s are becoming more popular day-by-day and replacing MSDB’s.
High Availability Large Databases (HALDB)
They were introduced as an IMS function extension for better availability and handling of extremely large data volumes and for online re-organization to support continuous availability (IMS V9) in IMS V7.
IMS is also one of the top three transaction managers which interacts with the end users while processing some function and ensures that all the data records are stored correct. The transaction manager uses a queuing technique for sending and receiving messages from a terminal with the help of a scheduler for proper recording of transactions.
Nowadays, the IMS works in tandem with the DB2 and provides a straight-forward and easy environment for transaction execution. This is because the IMS with its superior speed and DB2 with its superior design work best for all possible transactions. It has become so popular these days that even accessing an ATM can trigger an IMS operation.
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