tailieunhanh - Báo cáo khoa học: "Unsupervised Semantic Role Induction with Global Role Ordering"

We propose a probabilistic generative model for unsupervised semantic role induction, which integrates local role assignment decisions and a global role ordering decision in a unified model. The role sequence is divided into intervals based on the notion of primary roles, and each interval generates a sequence of secondary roles and syntactic constituents using local features. | Unsupervised Semantic Role Induction with Global Role Ordering Nikhil Garg University of Geneva Switzerland James Henderson University of Geneva Switzerland j Abstract We propose a probabilistic generative model for unsupervised semantic role induction which integrates local role assignment decisions and a global role ordering decision in a unified model. The role sequence is divided into intervals based on the notion of primary roles and each interval generates a sequence of secondary roles and syntactic constituents using local features. The global role ordering consists of the sequence of primary roles only thus making it a partial ordering. 1 Introduction Unsupervised semantic role induction has gained significant interest recently Lang and Lapata 2011b due to limited amounts of annotated corpora. A Semantic Role Labeling SRL system should provide consistent argument labels across different syntactic realizations of the same verb Palmer et al. 2005 as in a. Mark a0 drove the car ai b. The car ai was driven by Mark a0 This simple example also shows that while certain local syntactic and semantic features could provide clues to the semantic role label of a constituent nonlocal features such as predicate voice could provide information about the expected semantic role sequence. Sentence a is in active voice with sequence A0 PREDICATE A1 and sentence b is in passive voice with sequence A1 PREDICATE A0 . Additional global preferences such as arguments A0 and A1 rarely repeat in a frame as seen in the corpus could also be useful in addition to local features. 145 Supervised SRL systems have mostly used local classifiers that assign a role to each constituent independently of others and only modeled limited correlations among roles in a sequence Toutanova et al. 2008 . The correlations have been modeled via role sets Gildea and Jurafsky 2002 role repetition constraints Punyakanok et al. 2004 language model over roles .

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