Product Code Database
In computing, the network model is a database model conceived as a flexible way of representing objects and their relationships. Its distinguishing feature is that the database schema, viewed as a graph in which object types are nodes and relationship types are arcs, is not restricted to being a hierarchy or Lattice graph.
The network model was adopted by the CODASYL Data Base Task Group in 1969 and underwent a major update in 1971. It is sometimes known as the CODASYL model for this reason. A number of network database systems became popular on mainframe and through the 1970s before being widely replaced by relational databases in the 1980s.
The chief argument in favour of the network model, in comparison to the hierarchical model, was that it allowed a more natural modeling of relationships between entities. Although the model was widely implemented and used, it failed to become dominant for two main reasons. Firstly, IBM chose to stick to the hierarchical model with semi-network extensions in their established products such as IMS and DL/I. Secondly, it was eventually displaced by the relational model, which offered a higher-level, more declarative interface. Until the early 1980s the performance benefits of the low-level navigational interfaces offered by hierarchical and network databases were persuasive for many large-scale applications, but as hardware became faster, the extra productivity and flexibility of the relational model led to the gradual obsolescence of the network model in corporate enterprise usage.
Bachman's influence is recognized in the term Bachman diagram, a diagrammatic notation that represents a database schema expressed using the network model. In a Bachman diagram, named rectangles represent record types, and arrows represent one-to-many relationship types between records (CODASYL set types).
David M, k., 1997. Fundamentals, Design, and Implementation. database processing ed. s.l.:Prentice-Hall.
|
|
