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用半连接解决环关系查询

USING SEMIJOINS TO SOLVE CYCLIC RALATIONAL QUERIES
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摘要 半连接是从一个关系中选择出一组元组与另一个同该关系有相同连接域的关系中的一个或多个元组相匹配的一种关系代数运算。在文献中,已经提供了用半连接对树查询的求解手段;并指出对于环查询,一般无法用半连接求解;此外,还给出了一个快速测试树查询成员的算法。本文是在文献的基础上,对其进行扩充,即对环查询中的满足可由半连接进行求解的数据库状态求解。 Semi-join is a relational algebraic operation that selects a set of tuples inone relation that matches one or more tuples of another relation on the joining domains.In the paper [1] a solution using semi-joins for tree queries is provided;but it can notsolve cyclic queries problem by means of semi-join;in addition,a linear-timemembership test for tree queries is presented.Based on the paper referred,this paperdevelops the solution for cyclic queries with certain class of database states.
出处 《计算机应用与软件》 CSCD 1990年第2期10-16,共7页 Computer Applications and Software
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