Database Models

A database model describes the logical structure of a database — that is, the way the data is organised and how different pieces of data are related to one another. Over the years several models have been used:

• Hierarchical model: data is organised in a tree-like (parent–child) structure. Each 'child' record has exactly one 'parent', like the branches of a tree or an organisation chart. It is simple and fast for tree-shaped data but rigid — it cannot easily represent relationships where a record needs many parents.
• Network model: an extension of the hierarchical model in which a record can have more than one parent, so relationships are represented as a network (a graph) rather than a strict tree. It is more flexible than the hierarchical model but more complex to design and use.
• Relational model: data is organised into tables (also called relations) made up of rows and columns. Relationships between tables are created by matching values in common columns (keys), rather than by fixed physical links. This is by far the most widely used model today because it is simple to understand, flexible, and works naturally with the SQL query language.
• Object-oriented model: data is stored as objects, similar to the objects used in object-oriented programming, so that data and the operations on it are kept together. It is useful for complex data such as multimedia, but is less common for ordinary business records than the relational model. …