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In computer science, a term index is a data structure to facilitate fast lookup of terms and clauses in a logic program, deductive database, or automated theorem prover. Many operations in automatic theorem provers require search in huge collections of terms and clauses. Such operations typically fall into the following scheme. Given a collection of terms (clauses) and a query term (clause) , find in some/all terms related to according to a certain retrieval condition. Most interesting retrieval conditions are formulated as existence of a substitution that relates in a special way the query and the retrieved objects . Here is a list of retrieval conditions frequently used in provers: * term is unifiable with term , i.e., there exists a substitution , such that = * term is an instance of , i.e., there exists a substitution , such that = * term is a generalisation of , i.e., there exists a substitution , such that = * clause subsumes clause , i.e., there exists a substitution , such that is a subset/submultiset of * clause is subsumed by , i.e., there exists a substitution , such that is a subset/submultiset of More often than not, we are actually interested in finding the appropriate substitutions explicitly, together with the retrieved terms , rather than just in establishing existence of such substitutions. Very often the sizes of term sets to be searched are large, the retrieval calls are frequent and the retrieval condition test is rather complex. In such situations linear search in , when the retrieval condition is tested on every term from , becomes prohibitively costly. To overcome this problem, special data structures, called ''indexes'', are designed in order to support fast retrieval. Such data structures, together with the accompanying algorithms for index maintenance and retrieval, are called ''term indexing techniques''. ==Classic indexing techniques== * discrimination trees * substitution trees * path indexing 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「term indexing」の詳細全文を読む スポンサード リンク
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