The Semantics of Semantic Annotation

The Semantics of Semantic Annotation∗ Harry Bunt Department of Communication and Information Sciences, Tilburg University P.O.Box 90153, 5000 LE Tilburg, The Netherlands harry.bunt@uvt.nl Abstract. This is a speculative paper, describing a recently started effort to give a formal semantics to semantic annotation schemes. Semantic annotations are intended to capture certain semantic information in a text, which means that it only makes sense to use semantic annotations if these have a well-defined semantics. In practice, however, semantic annotation schemes are used that lack any formal semantics. In this paper we outline how existing approaches to the annotation of temporal information, semantic roles, and reference relations can be integrated in a single XML-based format and can be given a formal semantics by translating them into second-order logic. This is argued to offer an incremental aproach to the incorporation of semantic information in natural language processing that does not suffer from the problems of ambiguity and lack of robustness that are common to traditional approaches to computational semantics. Keywords: semantic annotation, semantic interpretation, temporal annotation, reference annotation, semantic roles, underspecified semantic representation. 1. Introduction The most interesting and challenging computer applications of natural language require the exploitation of semantic information. This is for example the case for intelligent spoken or multimodal dialogue systems, and for interactive question answering given a data base of natural language texts. Efforts to make computers exploit the semantics of utterances and texts have so far met with very limited success, however. This has two fundamental reasons: the ambiguity problem and the robustness problem. 1. The ambiguity problem: Computing the meaning conveyed by natural language expressions requires the availabilty of a vast amount and wide range of context information, such as knowledge of the domain of discourse, knowledge of the interactive (or other) setting in which language is used, knowledge of what occurred earlier in the discourse, knowledge of what nonlinguistic sources of information are available (e.g. shared visual context), and so on. In the absence of such information, natural language expressions are massively ambiguous; it has been estimated, for example, that a printed sentence of average length in Dutch or English has more than half a million possible readings when considered in isolation (Bunt and Muskens, 1999). Well-established methods of formal semantics, such as Montague-style or DRT-style semantics, capitalize on the context-independent interpretation of syntactic structure and function words, and have hardly any devices for taking context information into account. It may be noted that ∗ Thanks to Kiyong Lee for comments on an earlier version. Copyright 2007 by Harry Bunt 13 the ambiguity problem that arises in context-independent interpretation of natural language is to some extent artificial: it is in part caused by the aim to derive ‘disambiguated interpretations’ within the framework of a formal logical system, which brings a level of granularity which forces one to deal with issues that are often irrelevant in practical situations. 2. The robustness problem: The methods of formal semantics tend not to be robust enough when applied to practical uses …

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