Link Grammar ( by Davy Temperley,

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Link Grammar ( by Davy Temperley, Daniel Sleator
 John Lafferty )

• Syed Toufeeq Ahmed
• ASU

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An example

• Sentence The cat chased a snake
• Link Grammar Representation

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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
• Planarity The links do not cross.
• Connectivity The links connect to all the words
  of the sequence together.
• Satisfaction The links satisfy the linking
  requirement of each word in the sentence.
• Exclusion No two links may connect the same pair
  of words.

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Dictionary and the linking requirement of words
in it
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Dictionary encoding
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Previous example

• Sentence The cat chased a snake
• Link Grammar Representation

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Violation of rule 1 (planarity)

• The Mary chased cat

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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.

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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.

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Prepositions

• J,M and EV allow prepositional phrases.

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Participles

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

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Biomedical Example -- 1

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

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1
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Linkage
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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."

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References

• Daniel Sleator and Davy Temperley. 1991. Parsing
  English with a Link Grammar. Carnegie Mellon
  University Computer Science technical report ,
  1991.
• Daniel Sleator and Davy Temperley. 1993. Parsing
  English with a Link Grammar. Third International
  Workshop on Parsing Technologies
• John Lafferty, Daniel Sleator, and Davy
  Temperley. 1992. 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. 1995. A robust parsing algorithm for
  link grammars Proceedings of the Fourth
  International Workshop on Parsing Technologies,
  Prague, September, 1995