The network data model is a relational database model designed as a generic approach to representing various objects and their relations. Its defining characteristic is the schema, seen as an unqualified graphical graph where each object type is arc and relationship categories are nodes, are allowed to intersect with other nodes in the immediate network. Every node has at least one other node directly opposite it and every directed edge exists between any two directly opposite nodes. A directed edge exists if and only if all of the directed edges between any pair of nodes in the network have a common direction of travel. The arrows from any nodes in the network to any other node in the network depict the directed edges.
A basic property of the network data model is that each entity has a unique set of attributes. Attributes types that uniquely describe an entity. There are seven different attributes needed for any entity in the database. Each attribute corresponds to a particular database table and they can be numeric or text. The set-type occurrences are used to map the attributes onto the tables in the database.
The hierarchy in the network data model allows entities to be placed into different types and levels in the hierarchy. The most basic form of the hierarchy is the one parent entity that can have one or no sub-entities. Each of the sub-entities can be subordinate to the main entity. In a multi-parent entity, there may be one parent and three or more sub-entities.
A fully implemented network data model should include both the traditional hierarchy of tables and the fully operational relational model. In the relational model, there are primary and secondary relationships among objects. A primary relationship is one that links an entity together with another entity in a series. A secondary relationship is one that connects entities to one another based on some other characteristics of the entities.
Most of the networks that implement their own database models include both of these types of relationship. However, database models that do not include both of these types of relationship usually provide less flexibility than those that do. In general, these two types of organization are more compatible with the way business users to interface with their information. The network data model can provide the business user with an easier to use interface by removing the need to learn about the relational concepts. The database model can also provide a higher level of security.
When considering whether to implement a data model or to use a traditional database management system, it is important to remember that there are both advantages and disadvantages to both approaches. Network data modelling provides a solid organizational framework that is easy to understand and maintain. However, fully functional data models often provide a higher level of functionality than the data models that do not include a semantic layer.
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