What is a Network Model?

Oddly enough the Network model was designed to do what the Hierarchical model could not. Though both show how data is related the Network model allows for data to not only have many children but also many parents, where as the Hierarchical model allowed for only one parent with many children. With the Network model data relationships must be predefined.

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It was in 1971 that the Conference on Data System Languages or CODASYL officially or formally defined the Network model. This is essentially how the CODASYL defined the Network model:

The central data modeling theory in the network model is the set theory. A set contains a holder record style, a set title, and an affiliate record type.

An affiliate record type is able to have the same role in more than one set; because of this the multi-parent hypothesis is established. A holder record style can be an affiliate or holder in another set as well.

The data model is an uncomplicated system, and link and connection record styles (often referred to as junction records) may well be existent, as well as additional sets between them.

Therefore, the entire network of relationships is demonstrated by a number of pair wise sets; within each set some record type is holder or owner (meaning one record type) this will be located at the tail of the network arrow (See figure below for an example) and one or more of the record types are presented as members or affiliates (the will be located at the head of the relationship arrow). Usually, a set defines a 1: M relationship, although 1:1 is permitted.

The Traditional Network Model

The most notable advantage of the Network model is that in comparison with the Hierarchical model it allows for a more natural avenue to modeling relationships between information. Though the model has been widely used it has failed to dominate the world of data modeling.

This is believed to be due to large companies choosing to continue using the Hierarchical model with some alterations to accommodate their individual needs and because it had been made almost obsolete by the Relational Model which offers a higher lever, and a more declarative interface.

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For a while the performance benefits of the lower lever navigational interfaces used with the Hierarchical and Network models were well suited for most large applications.

Yet as hardware advanced and became faster the added productivity and flexibility of the newer models proved to be better equipped for the data needs.

Soon the Hierarchical and Network models were all but forgotten in relation to corporate enterprise usage.

Next Page: OSI Network Model