This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these template messages) This article includes a list of references, related reading, or external links, but its sources remain unclear because it lacks inline citations. Please help to improve this article by introducing more precise citations. (October 2008) (Learn how and when to remove this template message) This article relies largely or entirely on a single source. Relevant discussion may be found on the talk page. Please help improve this article by introducing citations to additional sources.Find sources: "Network model" – news · newspapers · books · scholar · JSTOR (January 2019) This article may be too technical for most readers to understand. Please help improve it to make it understandable to non-experts, without removing the technical details. (January 2019) (Learn how and when to remove this template message) (Learn how and when to remove this template message)
Bachman diagram of a simple network 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 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.

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 minicomputers through the 1970s before being widely replaced by relational databases in the 1980s.

Overview

While the hierarchical database model structures data as a tree of records, with each record having one parent record and many children, the network model allows each record to have multiple parent and child records, forming a generalized graph structure. This property applies at two levels: the schema is a generalized graph of record types connected by relationship types (called "set types" in CODASYL), and the database itself is a generalized graph of record occurrences connected by relationships (CODASYL "sets"). Cycles are permitted at both levels.

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.

History

The network model's original inventor was Charles Bachman, and it was developed into a standard specification published in 1969 by the Conference on Data Systems Languages (CODASYL) Consortium. This was followed by a second publication in 1971, which became the basis for most implementations. Subsequent work continued into the early 1980s, culminating in an ISO specification, but this had little influence on products.

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).

Database systems

Some well-known database systems that use the network model include:

See also

References

David M, k., 1997. Fundamentals, Design, and Implementation. database processing ed. s.l.:Prentice-Hall.

Further reading

External links

Wikimedia Commons has media related to Network models.
Database models
Categories