Jump to content

Relational database management system

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by Neilc (talk | contribs) at 22:31, 12 August 2004 (fix section titles (see manual of style)). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

A Relational Database Management System (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by Edgar F. Codd.

History of the term

Codd wrote a paper where he coined the term. In this paper and later papers he defined what he meant by Relational. Among other critera, there are Codd's 12 rules.

The first released RDBMS —that was a relatively faithful implementation of the relational model— was the Multics Relational Data Store, first sold in 1978. Others have been Berkeley Ingres QUEL and IBM BS12. In the '70s and '80s, it wasn't really possible to have a perfectly faithful implementation of Codd's definition of a Relational DBMS. Also, some think that it isn't a good idea to implement all of the rules. Because there weren't any DBMSs for so long that satisfied all of the rules, and people were calling the the DBMSs based on some of the principles Relational, the term has stuck.

Current usage

There have been many DBMSs that have been called relational by basing their DBMS on Codd's principles. There are two schools of thought on what can or can't be called a Relational DBMS.

The common usage, used by most of the industry, considers Oracle's Oracle database, Microsoft SQL Server, and MySQL relational databases, as they follow some of Codd's principles.

Popular commercial DBMSs that meet this qualification include Oracle, Microsoft SQL Server, Sybase SQL Server, IBM's DB2, and Microsoft Access. MySQL, PostgreSQL and Firebird are free DBMSs that are considered relational by this group.

The other usage, shared by many theorists, and strict adherents to Codd's principles, believe that because those DBMSs don't satisfy all the rules, they aren't relational. In fact, most successful DBMSs (including all DBMSs that use the Structured Query Language (SQL) as their primary language) that are considered to be relational violate the relational model in several important ways. Those who follow this interpretation think that to be called "relational", a DBMS must satisfy all of the rules. According to them, those DBMSs that do not follow all of the rules (like Oracle and MSSQL Server) are called Pseudo-Relational Database Management Systems (PRDBMS). For clarification, they often refer to DBMSs that do follow all of the rules Truly-Relational Database Management Systems. These adherents

Today, All of these DBMSs use SQL as their query language and therefore are not truly relational. Most have other rules they break also.

Alphora's Dataphor, is a commercially-available RDBMS that follows all of Codd's rules, and is considered a Relational DBMS by both groups. However, it is neither popular nor widespread.

  • Database Debunkings
    • Critical point of view that argues that it is important that the predicate relational should be reserved for those database systems that are fully faithful to the relational model. However, this is not the most common usage.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Relational_database_management_system&oldid=5172677"