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Codd's 12 rules
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== History == Codd originally set out the rules in 1970, and developed them further in a 1974 conference paper.<ref name="Kline">{{cite book |last1=Kline |first1=Kevin |last2=Gould |first2=Lee |last3=Zanevsky |first3=Andrew |title=Transact-SQL Programming: Covers Microsoft SQL Server 6.5 /7.0 and Sybase Adaptive Server 11.5 |date=1999 |isbn=9781565924017 |url=https://books.google.com/books?id=CWf1Pv6OeAcC&dq=Codd%27s+12+rules&pg=PA5 |access-date=22 January 2022}}</ref> His aim was to prevent the vision of the original relational database from being diluted, as database vendors scrambled in the early 1980s to repackage existing products with a relational veneer.{{citation needed|date=January 2022}} Rule 12 was particularly designed to counter such a positioning.{{citation needed|date=January 2022}} While in 1999, a textbook stated "Nowadays, most RDBMSs ... pass the test",<ref name="Kline"/> another in 2007 suggested "no database system complies with all twelve rules."<ref name="Hess">{{cite book |last1=Hess |first1=Kenneth |title=Microsoft Office Access 2007: The L Line, The Express Line to Learning |date=2007 |isbn=9780470107904 |url=https://books.google.com/books?id=BMnZ0Q7nR6gC&dq=Codd%27s+12+rules&pg=PA169 |access-date=22 January 2022}}</ref> Codd himself, in his book "The Relational Model for Database Management: Version 2", acknowledged that while his original set of 12 rules can be used for coarse distinctions, the 333 features of his Relational Model Version 2 (RM/V2) are needed for distinctions of a finer grain.<ref name="Codd">{{cite book |last1=Codd |first1=Edgar F. |title=The Relational Model for Database Management: Version 2 |publisher=Addison-Wesley Longman Publishing Co., Inc. |year=1990 |isbn=9780201141924 |url=https://books.google.com/books?id=ZZckAQAAIAAJ}}</ref>
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