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In [[computer science]], '''term indexing''' is the task of creating an [[index (search engine)|index]] of terms and clauses in a collection.
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Many operations in automatic [[Automated theorem prover|theorem prover]]s require search in huge
collections of terms and clauses. Such operations typically fall into
the following scheme. Given a collection <math>S</math> of terms (clauses) and a query
term (clause) <math>q</math>, find in <math>S</math> some/all terms <math>t</math> related to <math>q</math> 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 <math>t</math>. Here is a list of retrieval
conditions frequently used in provers:
 
* term <math>q</math> is unifiable with term <math>t</math>, i.e., there exists a substitution <math> \theta </math>, such that <math>q\theta</math> = <math>t\theta</math>
* term <math>t</math> is an instance of <math>q</math>, i.e., there exists a substitution <math>\theta</math>, such that <math>q\theta</math> = <math>t</math>
* term <math>t</math> is a generalisation of <math>q</math>, i.e., there exists a substitution <math>\theta</math>, such that <math>q</math> = <math>t\theta</math>
* clause <math>q</math> subsumes clause <math>t</math>, i.e., there exists a substitution <math>\theta</math>, such that <math>q\theta</math> is a subset/submultiset of <math>t</math>
* clause <math>q</math> is subsumed by <math>t</math>, i.e., there exists a substitution <math>\theta</math>, such that <math>t\theta</math> is a subset/submultiset of <math>q</math>
More often than not, we are actually interested in finding the appropriate
substitutions explicitly, together with the retrieved terms <math>t</math>,
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 <math>S</math>, when the retrieval
condition is tested on every term from <math>S</math>, 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 tree]]s
* [[substitution tree]]s
* [[path indexing]]
 
==Modern indexing techniques==
 
* [[feature vector indexing]]
* [[code tree]]s
* [[context tree]]s
* [[relational path indexing]]
 
==Further reading==
* P. Graf, Term Indexing, Lecture Notes in Computer Science 1053, 1996 (slightly outdated overview)
* R. Sekar and I.V. Ramakrishnan and A. Voronkov, Term Indexing, in A. Robinson and A. Voronkov, editors, [[Handbook of Automated Reasoning]], volume 2, 2001 (recent overview)
* W. W. McCune, Experiments with Discrimination-Tree Indexing and Path Indexing for Term Retrieval, Journal of Automated Reasoning, 9(2), 1992
* P. Graf, Substitution Tree Indexing, Proc. of RTA, Lecture Notes in Computer Science 914, 1995
* M. Stickel, The Path Indexing Method for Indexing Terms, Tech. Rep. 473, [[Artificial Intelligence Center]], [[SRI International]], 1989
* S. Schulz, Simple and Efficient Clause Subsumption with Feature Vector Indexing, Proc. of IJCAR-2004 workshop ESFOR, 2004
* A. Riazanov and A. Voronkov, Partially Adaptive Code Trees, Proc. JELIA, Lecture Notes in Artificial Intelligence 1919, 2000
* H. Ganzinger and R. Nieuwenhuis and P. Nivela, Fast Term Indexing with Coded Context Trees, Journal of Automated Reasoning, 32(2), 2004
* A. Riazanov and A. Voronkov, Efficient Instance Retrieval with Standard and Relational Path Indexing, Information and Computation, 199(1–2), 2005
 
{{DEFAULTSORT:Term Indexing}}
[[Category:Searching]]
 
[[fr:Index terminologique]]
[[pl:Indeksowanie termów]]

Latest revision as of 21:59, 11 January 2015

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