Semantic Affinity

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Semantic Affinity of a linguistic-pattern is a measure for judging the effectiveness of that pattern in extracting the required Noun-Phrases belonging to a semantic class. The term was first used by Patwardhan and Riloff in their paper on learning domain-specific IE patterns from the web.
Mathematically semantic affinity for a pattern is defined as:


where is the frequency of occurrence of the pattern where it had a noun-phrase from the semantic class "class", and is the total frequency of occurrence of that pattern in the corpus.