本文介绍在演绎数据库中语义查询优化方法。
This paper introduces an approach to semantic query optimization in deductive database.
重写是一种优化策略，它将一个有效的查询转化成语义上相等的一种新形式，这种新的形式执行起来更为高效。
Rewrite is an optimization strategy that transforms a valid query into a semantically equivalent form that can be more efficient to execute.
在某些环境下，优化器不能将一个 ATQ 放在一个 SHIP 操作符之上，因为这样会改变查询的语义。
Under certain circumstances,it is not possible for the optimizer to place an ATQ above a SHIP operator because doing so changes the semantics of the query.
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