The Semijoin Algebra and the Guarded Fragment
The Semijoin Algebra and the Guarded Fragment
复制标题
半连接代数和保护片段
DOI：
10.1007/s10849-005-5789-8
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
J. V. D. Bussche
中科院分区：
文献类型：
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作者：
Dirk Leinders;M. Marx;Jerzy Tyszkiewicz;J. V. D. Bussche
在1970年代，CODD引入了关系代数，并以操作员的选择，投影，联合，差异和产品，表明它等同于一阶逻辑，我们表明，如果我们在Codd的关系代数中取代产品运营商，则通过“ Semijoin”运算符，然后由此产生的“ Semijoin代数”等同于一阶逻辑的守卫片段。对应于μgf。
In the 1970s Codd introduced the relational algebra, with operators selection, projection, union, difference and product, and showed that it is equivalent to first-order logic. In this paper, we show that if we replace in Codd’s relational algebra the product operator by the “semijoin” operator, then the resulting “semijoin algebra” is equivalent to the guarded fragment of first-order logic. We also define a fixed point extension of the semijoin algebra that corresponds to μGF.