约束检查的最弱及增量前条件方法

约束检查是保持数据库语义合法性的关键环节．由于在事务执行后直接检查约束的代价太大，一般通过分析对数据库的修改和约束公式得出简化的测试条件，只要在修改前检查其能否成立就可以确定修改后数据库是否满足约束．给出计算这种约束检查条件的最弱及增量前条件方法，分别用于生成充要及充分测试条件．后者利用当前数据库状态满足约束的假设通常得出较简单的条件．与其他技术相比，这一方法处理的约束和事务种类更一般，测试条件的生成也更有效．

Weakest and Incremental Preconditions for Constraint Checking

Constraint checking plays a critical role in maintaining validity of database semantics Straightforward verification of the constraintsafter each transaction is very expensive An alternative approachis to derive a simplified condition from the involvedtransaction and constraint, which can be checked before theupdate to ensure the constraint holds after the update A method based on weakest and incremental precondition is givenfor efficiently calculating necessary and sufficient conditionsfor such test Sufficient conditions are generally simpler to evaluate with the assumption that the constraint holds in currentdatabase state This method deals with more general constraintsand transactions than other approaches do and the derivation oftest conditions is more effective