Link Grammar ( by Davy Temperley, Daniel Sleator & John Lafferty ) Syed Toufeeq Ahmed ASU

An example Sentence: “The cat chased a snake” Link Grammar Representation:

Link Grammar (LG) Sequence of words is in the language of link grammar if there is a way to draw links between words in such a way that 1. Planarity : The links do not cross. 2. Connectivity : The links connect to all the words of the sequence together. 3. Satisfaction: The links satisfy the linking requirement of each word in the sentence. 4. Exclusion: No two links may connect the same pair of words.

Dictionary and the linking requirement of words in it

Dictionary encoding

Previous example Sentence: “The cat chased a snake” Link Grammar Representation:

Violation of rule 1 (planarity) “ The Mary chased cat ”

LG formalisms and properties Each word of lexicon has definition describing how it has to be used. (Lexical) After parsing, words that are associated semantically and syntactically are directly linked In English, whether or not a noun needs a determiner is independent of whether it is used as a subject or an object. According to LG dictionary, ‘cat’ can be used in 369 different ways, ‘time’ – 1689 different ways. No explicit notion of constituents or categories.

Difficult situations Coordinating conjunctions such as ‘and ’ in “The dog chased and bit Mary”, here links would cross. Non-referential use of ‘it ’. “It is likely that John will go” is correct. “The cat is likely that John will go” is incorrect. The Parser fails here, there is a Post-Processor to handle these situations.

Prepositions J,M and EV allow prepositional phrases.

Participles M- connector on chased, participle phrase modifying noun.

Biomedical Example -- 1 "GABA mediates the inhibitory effect of NO on the AVP and OXT responses to insulin- induced hypoglycemia."

Linkage 1 2

Bio-text example 2 “We demonstrate that INSULIN treatment results in activation of both PLD1 and PLD2 in appropriate cell types when the appropriate upstream intermediate signalling components, i.e. PKCalpha and PLCgamma, are expressed at sufficient levels."

References Daniel Sleator and Davy Temperley Parsing English with a Link Grammar. Carnegie Mellon University Computer Science technical report, Daniel Sleator and Davy Temperley Parsing English with a Link Grammar. Third International Workshop on Parsing Technologies John Lafferty, Daniel Sleator, and Davy Temperley Grammatical Trigrams: A Probabilistic Model of Link Grammar. Proceedings of the AAAI Conference on Probabilistic Approaches to Natural Language, October, 1992 Dennis Grinberg, John Lafferty and Daniel Sleator A robust parsing algorithm for link grammars Proceedings of the Fourth International Workshop on Parsing Technologies, Prague, September, 1995