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# 14. THE POSTGRES RULE SYSTEM

Production rule systems are conceptually simple, but there are many subtle points involved in actually using them. Consequently, we will not attempt to explain the actual syntax and operation of the POSTGRES rule system here. Instead, you should read [STON90b] to understand some of these points and the theoretical foundations of the POSTGRES rule system before trying to use rules. The discussion in this section is intended to provide an overview of the POSTGRES rule system and point the user at helpful references and examples. The "query rewrite" rule system modifies queries to take rules into consideration, and then passes the modified query to the query optimizer for execution. It is very powerful, and can be used for many things such as query language procedures, views, and versions. The power of this rule system is discussed in [ONG90] as well as [STON90b].

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