Some questions (doubts) about STS(mostly from the perspective of distributional semantics)

Alessandro Lenci

University of Pisa

What is semantic similarity?• Is semantic similarity a well-grounded notion?

Perhaps no...– for concepts?

• cf. Goodman’s argument that similarity is empty unless you specify “similar with respect to what”

– for lexical items?• partially

– word similarity judgments hide many different types of semantic relations (cf. Rubinstein and Goodenough)

– for phrases and sentences?• ??

– but we know some relations between sentences (e.g. entailment, contradiction, presupposition, etc.)

Which (basic) components for STS?

• Module for word-level semantic similarity

• Module for “compositional” semantic similarity– do we know how to project semantic

similarity from the word level to sentence or text level?

From semantic similarity to semantic relations (in distributional semantics)

• Lexical entailment (cf. Dagan et al.)• “Classical” semantic relations• e.g. hypernymy, antonymy, etc.

– some words are very similar under one respect (e.g. increase / decrease, open / close, etc.) but express highly dissimilar concepts, etc.

– some texts can share most of their words, and still be very different

• Most students like to go dancing on Saturday.• Few students like to go dancing on Saturday.• Most students hate to go dancing on Saturday.

What to do?

• Prepare carefully designed and controlled data sets– explore different dimensions of variation with

respect to text similarity• function words, lexical items, syntax, etc.

– explore different types of relations between texts covered by STS

• Analyse the factors that affect the judgments of STS