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Query (complexity)
In descriptive complexity, a query is a mapping from structures of one signature to structures of another vocabulary. Neil Immerman, in his book "Descriptive Complexity", "use() the concept of query as the fundamental paradigm of computation" (p. 17).
Given signatures and , we define the set of structures on each language, and . A query is then any mapping
Computational complexity theory can then be phrased in terms of the power of the mathematical logic necessary to express a given query.
==Order-independent queries==
A query is order-independent if the ordering of objects in the structure does not affect the results of the query. In databases, these queries correspond to generic queries (Immerman 1999, p. 18). A query is order-independent iff for any isomorphic structures and .
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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