relational database

database (RDBMS - relational database management system) A

database based on the relational model developed by

E.F. Codd. A relational database allows the definition of

data structures, storage and retrieval operations and

integrity constraints. In such a database the data and

relations between them are organised in tables. A table is

a collection of rows or records and each row in a table

contains the same fields. Certain fields may be designated

as keys, which means that searches for specific values of

that field will use indexing to speed them up.

Where fields in two different tables take values from the same

set, a join operation can be performed to select related

records in the two tables by matching values in those fields.

Often, but not always, the fields will have the same name in

both tables. For example, an "orders" table might contain

(customer_id, product_code) pairs and a "products" table might

contain (product_code, price) pairs so to calculate a given

customer's bill you would sum the prices of all products

ordered by that customer by joining on the product-code fields

of the two tables. This can be extended to joining multiple

tables on multiple fields. Because these relationships are

only specified at retreival time, relational databases are

classed as dynamic database management system.

The first commercial RDBMS was the Multics Relational DataStore, first sold in 1978.

INGRES, Oracle, Sybase, Inc., Microsoft Access, and

Microsoft SQL Server are well-known database products and

companies. Others include PostgreSQL, SQL/DS, and RDB.

["Managing Data Bases, Four Critical Factors" Michael

M. Gorman, QED Information Sciences, Inc.].

["An Introduction To Database Systems" (6th ed) C. J. Date,

Addison Wesley (an excellent source of detailed info)].

["An End-User's Guide to Data Base" James Martin, Prentice

Hall (excellent place to begin learning about DBMS)].

(2002-06-10)