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Codd introduced the term in his seminal paper A Relational Model of Data for Large Shared Data Banks. In this paper and later papers he defined what he meant by relational. One well-known definition of what constitutes a relational database system is Codd's 12 rules. However, many of the early implementations of the relational model did not conform to all of Codd's rules, so the term gradually came to describe a broader class of database systems. At a minimum, these systems:
The first 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.
There is some disagreement about what can or cannot be called a "relational" DBMS.
The most popular definition of a RDBMS is relatively imprecise; some argue that merely presenting a view of data as a collection of rows and columns is sufficient to qualify as a RDBMS. Typically, products that qualify as a RDBMS under this interpretation implement some of Codd's 12 rules, but most popular database systems do not support them all.
Popular commercial DBMSs sold as RDBMSs include Oracle, Microsoft SQL Server, Sybase SQL Server, IBM's DB2, and Microsoft Access. MySQL, PostgreSQL and FirebirdFirebird (sometimes called FirebirdSQL) is a relational database offering many ANSI SQL-92 and SQL-99 features that runs on Linux, Windows, and a variety of Unix platforms. Firebird is released under the InterBase Public License a modification of the open are free RDBMSs.
A second school of thought argues that if a database does not implement all of Codd's rules, it is not relational. This view, shared by many theorists and other strict adherents to Codd's principles, would disqualify many database systems from being considered "truly relational". In fact, any database that uses the Structured Query Language (SQL) to access and modify data is not an RDBMS under this definition. Advocates of this philosophy refer to systems that follow some but not all of the rules as 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 (TRDBMS).
Recently, the choice of RDBMS has become much less dependent on meeting all of Codd's 12 rules and much more dependent on providing a manageable Total cost of ownershipTotal cost of ownership (TCO is a type of calculation designed to help consumers and enterprise managers assess direct and indirect costs as well as benefits related to the purchase of computer software or hardware. A TCO ideally offers a final statement to data managementData management comprises all the disciplines related to managing data as a valuable resource. Topics: Data modeling Database administration Data warehousing Data movement Data mining Data quality assurance Data security Meta-data management (data reposit organizations within IT organizations. Today, all RDBMSs with any degree of popularity employ SQLStructured Query Language SQL is the most popular computer language used to create, modify and query databases. Technically, SQL is a declarative computer language for use with "quasi- relational databases". Theorists note that many of the original SQL fe as their query language.
Alphora's DataphorDataphor is a Relational Database Management System. It also is considered a Virtual DBMS, as well as a Truly-Relational DBMS. External links Database management systems. 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.
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