|
The network model is a database model conceived as a flexible way of representing objects and their relationships. Its original inventor was Charles Bachman, and it was developed into a standard specification published in 1969 by the CODASYL Consortium. Where the hierarchical 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 lattice structure. The chief argument in favour of the network model, in comparison to the hierarchic 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 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 relational systems pushed the network model out of the enterprise database world. The navigational interface offered by the network model bears some resemblance to the hyperlink-based models that have become popular with the advent of the Internet and World Wide Web. However, the network model (like the relational model) assumes that the entire database has a centrally-managed schema, and as such it is not well suited to distributed, heterogeneous environments.
History In 1969, the Conference on Data Systems Languages (CODASYL) established the first specification of the network database model. 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. See also | ||||||||
|
| |||||||||
 |
|
| |