As more research disciplines and social sectors are becoming computerized, an increasing amount of observational data and documentation are digitized. To support interchange of these digital materials, encoding standards such as XML (extended Markup Language) (W3C 2004a) have been proposed for digital document markup. A document structure is realized by a set of element tags that can be used to delimit data items in a document of the specific domain. If all the delimiting tags are properly placed in a document, the document is said to be well-formed. However, whether an XML document is valid is determined by the Document Type Definition (DTD), a formal grammar for specifying the structure and permissible values of XML documents. The content of the document elements and their markups can be specified and validated by a schema language, such as the XML Schema (Thompson et al. 2000), RELAX (Makoto 2000), or SOX (Davidson 1999). The tag set of a specific domain is called the “vocabulary” of that domain. People of the same domain could use the same basic syntax, parsers, and assisting tools of the vocabulary. This opens a way for different types of document structures to be created to facilitate communications for various professional domains. Digital data is thus not only represented but also defined in different languages.
KeywordsModel Management Graph Transformation Reference Element Document Structure Graph Grammar
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