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<Chapter>
<Title>The <ProductName>Postgres</ProductName> Rule System</Title>
<Para>
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 <ProductName>Postgres</ProductName> rule system
here. Instead, you should read
<XRef LinkEnd="STON90b" EndTerm="[STON90b]"> to understand
some of these points and the theoretical foundations of
the <ProductName>Postgres</ProductName> rule system before trying to use rules.
The discussion in this section is intended to provide
an overview of the <ProductName>Postgres</ProductName> 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
<XRef LinkEnd="ONG90" EndTerm="[ONG90]">
as well as
<XRef LinkEnd="STON90b" EndTerm="[STON90b]">.
</Para>
</Chapter>
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