Relational database
A relational database is a database based on the relational model, this means a relational database takes the form of a specific collection of data. The database software that is used to manage the data is called a relational database management system, or RDBMS.
The relational model was invented by Dr. Ted Codd as a general model of data. Codd himself proposed a three-valued logic version of the relational model, and a four-valued logic version has also been proposed, in order to deal with missing information. The relational data model permits the designer to create a consistent logical model of information, to be refined through database normalization. The access plans and other implementation and operation details are handled by the DBMS engine, and should not be reflected in the logical model. This contrasts with common practice for SQL DBMSs in which performance tuning often requires changes to the logical model.
The basic principle of the relational model is the Information Principle: all information is represented by data values in relations. Thus, the relvars are not related to each other at design time: rather, designers use the same domain in several relvars, and if one attribute is dependent on another, this dependency is enforced through referential integrity.
An idealized, very simple example of a description of some relvars and their attributes:
- Customer(Customer ID, Tax ID, Name, Address, City, State, Zip, Phone)
- Order(Order No, Customer ID, Invoice No, Date Placed, Date Promised, Terms, Status)
- Order Line(Order No, Order Line No, Product Code, Qty)
- Invoice(Invoice No, Customer ID, Order No, Date, Status)
- Invoice Line(Invoice No,Line No,Product Code, Qty Shipped)
Relational databases address all these points. They permit wildcard and logical expression searches, multiple searchable columns, and joins to represent relationships.
Updated On: 15.02.13