| |
One of several design models for databases. Databases allow users to store and access complex information without needing to know the details of the information\'s arrangement in storage. In the relational model, all information is expressed in the form of rectangular tables. The rows of tables correspond to instances of a particular type of record, and the columns to variables. For example, an airline\'s reservation database might include tables of flights, aircraft, passengers, and crew; each table would include the appropriate attributes (for flights, the departure airport and time, arrival airport and time, aircraft assigned to the flight, number of seats etc.). Tables are linked by \'common keys\'; for example, flight numbers would link flight data to passenger data. The relational model is well-suited to statistical data, such as those collected and disseminated by a census; and to geographical information systems (GIS), where its use has been identified with the term georelational model.
The relational model was originally described by Date (1975). In recent years numerous limitations of the model have led to interest in object-oriented databases (Cattell, 1994), although the relational model still dominates in many applications, including GIS. Object-oriented databases can include many features not found in relational databases, including the ability of objects to \'inherit\' properties from other objects, and the ability to define new types of objects, and many of these are of potential value in GIS. But object-oriented databases are largely limited to research prototypes at this time. (MG)
References Cattell, R.G.G. 1994: Object data management: object-oriented and extended relational database systems. Reading, MA: Addison-Wesley. Date, C.J. 1975: An introduction to database systems. Reading, MA: Addison-Wesley. |
|
