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Incomputing, thenetwork model is adatabase model conceived as a flexible way of representing objects and their relationships. Its distinguishing feature is that theschema, viewed as agraph in which object types are nodes and relationship types are arcs, is not restricted to being a hierarchy orlattice.
The network model was adopted by theCODASYLData Base Task Group in 1969 and underwent a major update in 1971. It is sometimes known as theCODASYL model for this reason. A number of network database systems became popular onmainframe andminicomputers through the 1970s before being widely replaced byrelational databases in the 1980s.
While thehierarchical database model structures data as atree ofrecords, with each record having one parentrecord 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. Peer-to-Peer and Client Server are examples of Network Models.
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 withsemi-network extensions in their established products such asIMS and DL/I. Secondly, it was eventually displaced by therelational 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.
The network model's original inventor wasCharles 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 anISO specification, but this had little influence on products.
Bachman's influence is recognized in the termBachman 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).
Some well-known database systems that use the network model include:
