[Semantic Web]Formal Semantics

读书笔记,  电脑与网络 Lee 发表于 2006/5/19 13:01:12 　 Humans communicate mostly through language. Natural language, however, is inherently ambiguous—semantically, but also syntactically. Computers lack the ability to disambiguate and understand complex natural language. For these reasons, it is infeasible to use natural language as a means for machines to communicate with other machines. As a first step, statements or facts need to be expressed in a way that computers can process them. Semantics that are represented in some well-formed syntactic form (governed by syntax rules) is referred to as formal semantics. There are some necessary and sufficient features that make a language formal and by association their semantics formal. These features include:   • The Notions of Model and Model Theoretic Semantics: Expressions in a formal language are interpreted in models. The structure common to all models in which a given language is interpreted (the model structure for the model-theoretic interpretation of the given language) reflects certain basic presuppositions about the “structure of the world” that are implicit in the language. • The Principle of Compositionality: The meaning of an expression is a function of the meanings of its parts and of the way they are syntactically combined. In other words, the semantics of an expression is computed using the semantics of its parts, obtained using an interpretation function. From a less technical perspective, formal semantics means machine processable semantics where the formal language representing the semantics has the above-mentioned features. Basically, the semantics of a statement are unambiguously expressed in the syntax of the statement in the formal language. A very limited subset of natural language is thus made available for computer processing.   Examples of such semantics are: • The semantics of subsumption in Description Logics, reflecting the human tendency of categorizing by means of broader or narrower descriptions. • The semantics of Partonomy, accounting for what is part of an object, not which category the object belongs to.

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