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HISTORY OF THE TERM 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 systems that were relatively faithful implementations of the relational model were from the IBM UK Scientific Centre at Peterlee; IS1 (1970–1972) and its followon PRTV (1973–1979). The first system sold as an RDBMS was Multics Relational Data Store , first sold in 1978 . Others have been Berkeley Ingres QUEL and IBM BS12 . CURRENT USAGE There is some disagreement about what a "relational" DBMS is. The most popular definition of an RDBMS is imprecise and not strictly based on Relational Theory ; some argue that merely presenting a view of data as a collection of rows and columns is sufficient to qualify as an RDBMS. Typically, products that qualify as an RDBMS under this interpretation implement some of Codd's 12 rules, but no popular database system supports them all. A second, theory-based school of thought argues that if a database does not implement all of Codd's rules (or the current understanding on the relational model, as expressed by Christopher J Date , Hugh Darwen and others), it is not relational. This view, shared by many theorists and other strict adherents to Codd's principles, would disqualify most DBMSs as not relational. For clarification, they often refer to RDBMSs as ''Truly-Relational Database Management Systems'' (TRDBMS). Today, almost all DBMSs employ SQL as their query language, but alternatives have been proposed and implemented. Alphora 's Dataphor is a commercially available RDBMS that follows all of Codd's rules — both groups recognizing it as a RDBMS. SEE ALSO
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