Editing Link grammar (section)

== Overview ==
Link grammar connects the words in a sentence with links, similar in form to a [[Catena (linguistics)|catena]]. Unlike the catena or a traditional [[dependency grammar]], the marking of the head-dependent relationship is optional for most languages, becoming mandatory only in [[word order|free-word-order languages]] (such as [[Turkish language|Turkish]],<ref>{{cite thesis |author=Özlem İstek |url=http://www.cs.bilkent.edu.tr/~ilyas/PDF/THESES/ozlem_istek_thesis.pdf |title=A Link Grammar for Turkish |type=Master's thesis |publisher=Bilkent University |place=Ankara, Turkey |year=2006 |access-date=2023-08-23}}</ref>{{better source needed|date=August 2023}} [[Finnish language|Finnish]], [[Hungarian language|Hungarian]]).  That is, in English, the subject-verb relationship is "obvious", in that the subject is almost always to the left of the verb, and thus no specific indication of dependency needs to be made.  In the case of [[subject-verb inversion]], a distinct link type is employed.  For free word-order languages, this can no longer hold, and a link between the subject and verb must contain an explicit directional arrow to indicate which of the two words is which.

Link grammar also differs from traditional dependency grammars by allowing [[cycle (graph theory)|cyclic relations]] between words.  Thus, for example, there can be links indicating both the head verb of a sentence, the head subject of the sentence, as well as a link between the subject and the verb. These three links thus form a cycle (a triangle, in this case). Cycles are useful in constraining what might otherwise be ambiguous parses; cycles help "tighten up" the set of allowable parses of a sentence.

For example, in the parse

     +---->WV--->+       
     +--Wd--+-Ss-+--Pa--+
     |      |    |      |
 LEFT-WALL he  runs   fast

the LEFT-WALL indicates the start of the sentence, or the root node. The directional '''WV''' link (with arrows) points at the head verb of the sentence; it is the Wall-Verb link.<ref>[http://www.abisource.com/projects/link-grammar/dict/section-WV.html WV Link type]</ref> The Wd link (drawn here without arrows) indicates the head noun (the subject) of the sentence. The link type '''Wd''' indicates both that it connects to the wall (W) and that the sentence is a declarative sentence (the lower-case "d" subtype).<ref>[http://www.abisource.com/projects/link-grammar/dict/section-W.html W link type]</ref>  The '''Ss''' link indicates the subject-verb relationship; the lower-case "s" indicating that the subject is singular.<ref>[http://www.abisource.com/projects/link-grammar/dict/section-S.html S link type]</ref> Note that the WV, Wd and Ss links for a cycle. The Pa link connects the verb to a complement; the lower-case "a" indicating that it is a [[predicative adjective]] in this case.<ref>[http://www.abisource.com/projects/link-grammar/dict/section-P.html P link type]</ref>