关键词: SGML, XML, 标记, 语义, 知识表示

Abstract:

　Although XML Document Type Definitions provide a mechanism for specifying, in machine-readable
form, the syntax of an XML markup language, there is no comparable mechanism for specifying the semantics
of an XML vocabulary. That is, there is no way to characterize the meaning of XML markup so that the facts and
relationships represented by the occurrence of XML constructs can be explicitly, comprehensively, and mechanically
identified. This has serious practical and theoretical consequences. On the positive side, XML constructs can be
assigned arbitrary semantics and used in application areas not foreseen by the original designers. On the less positive
side, both content developers and application engineers must rely upon prose documentation, or, worse, conjectures
about the intention of the markup language designer — a process that is time-consuming, error-prone, incomplete,
and unverifiable, even when the language designer properly documents the language. In addition, the lack of a
substantial body of research in markup semantics means that digital document processing is undertheorized as an
engineering application area. Although there are some related projects underway (XML Schema, RDF, the Semantic
Web) which provide relevant results, none of these projects directly and comprehensively address the core problems
of XML markup semantics. This paper (i) summarizes the history of the concept of markup meaning, (ii) characterizes
the specific problems that motivate the need for a formal semantics for XML and (iii) describes an ongoing research
project ： the BECHAMEL Markup Semantics Project —that is attempting to develop such a semantics.