Historical Development of Databases (Cont.)

First Generation (since late 1960s) (Cont.)
Network data model
A generalization of the hierarchical model where a set of records in one layer might have two different containing hierarchies at the next layer up. In short, the network model structured data as a directed graph without circuits.


The Cullinet Software’s IDMS (Integrated Database Management System) is a network database based on CODASYL (COnference on DAta SYstems Languages) report. The network model represents certain real-world data structures more easily than was possible in the hierarchical model.

The main drawback for network databases is also the queries against the data are difficult to create, normally requiring a program written by an expert programmer who understood what could be a complex navigational structure of the data.
Review: Historical Development of Databases
    Which statement is NOT true about databases?

      IBM’s DB2 was the world’s leading mainframe hierarchical data system.
      The Cullinet Software’s IDMS is a network database based on CODASYL report.
      The hierarchical model structured data as a directed tree.
      The network model structured data as a directed graph without circuits.
        Result:




      The best way to predict the future is to create it.