UNIT 1: BASIC CONCEPTS OF DATABASE MANAGEMENT SYSTEMS

Objects are the basic run-time entities in an object-oriented system. A number of general-purpose database systems emerged due to growth in the speed and capability of computers; by the mid-1960s there were a number of such systems in commercial use. Interest in a standard began to grow, and Charles Bachman, founded the ―Database Task Group‖ within CODASYL, the group responsible for the creation and standardization of COBOL. In 1971 they delivered their standard, which generally became known as the ―Codasyl approach‖, and soon there were a number of commercial products based on it available.

The Codasyl approach was based on the ―manual‖ navigation of a linked data set which was formed into a large network. To find any particular record the programmer had to step through these pointers one at a time until the required record was returned. Simple queries like ―find all the people in India‖ required the program to walk the entire data set and collect the matching results. There was, essentially, no concept of ―find‖ or ―search‖. This might sound like a serious limitation today, but in an era when the data was most often stored on magnetic tape such operations were too expensive to contemplate anyway.

IBM also had their own DBMS system in 1968, known as IMS. IMS was a development of software written for the Apollo program on the System/360. IMS was generally similar in concept to Codasyl, but used a strict hierarchy for its model of data navigation instead of Codasyl‘s network model. Both concepts later became known as navigational databases due to the way data was accessed, and Bachman‘s 1973 Turing Award presentation was The Programmer as Navigator. IMS is classified as a hierarchical database. IMS and IDMS, both CODASYL databases, as well as CINCOMs TOTAL database are classified as network databases.