A database is a collection of information called "data." In this context, a DBM, or a database management system, is the software used to organize and retrieve the information stored in the database.
Information in a database is stored according to rules, known as data models, that allow for rapid retrieval of information. The four basic models are relational, hierarchical, object and network. The type of information stored and its natural organization often determine the model used.
Relational databases use tables, with columns and rows, and keys to make each row in the table unique. Keys allow for faster retrieval of information and can link related information in different tables. Hierarchical databases use an inverted tree-like structure. This structure is popular for use with school systems; each school is a branch, each grade is a branch off the school branch, and information for individual students is stored in nodes. This system tends to be inflexible to changes in an organization.
The object model ensures that the database model is the same as the database model the application uses. Most application programs treat information as an object rather than a table. The network model is a newer type that uses elements of different existing models to connect related information. For example, it incorporates some of the methods of hierarchical database organization, but it is much more flexible.