Editing Prolog (section)

=== Term indexing ===
{{Main|Term indexing}}
Finding clauses that are unifiable with a term in a query is linear in the number of clauses. [[Term indexing]] uses a [[data structure]] that enables [[Sublinear time|sub-linear-time]] lookups.<ref>{{Cite book |last1=Graf |first1=Peter |title=Term indexing |year=1995 |publisher=Springer |isbn=978-3-540-61040-3}}</ref> Indexing only affects program performance, it does not affect semantics. Most Prologs only use indexing on the first term, as indexing on all terms is expensive, but techniques based on ''field-encoded words'' or ''[[Superimposed code|superimposed]] codewords'' provide fast indexing across the full query and head.<ref name=WisePowers>{{cite conference |last1=Wise |first1=Michael J. |last2=Powers |first2=David M. W. |title=Indexing Prolog Clauses via Superimposed Code Words and Field Encoded Words |journal=International Symposium on Logic Programming |pages=203–210 |year=1986}}</ref><ref name=Colomb>{{Cite journal |doi=10.1016/0743-1066(91)90004-9 |title=Enhancing unification in PROLOG through clause indexing |journal=The Journal of Logic Programming |volume=10 |pages=23–44 |year=1991 |last1=Colomb |first1=Robert M. |doi-access =}}</ref>