Community-Wide Markup Languages
Community size is inversely proportional to shared context
- Millions agree that <B> means bold, but “2/6/98” reflects local culture
- XML decentralizes control of specialized markup languages, making it cost-effective to capture community ontologies
HTML is not unilaterally extensible -- new tags potentially have ambiguous syntax, style, and semantics
XML is a strict (but simplified) subset of SGML, offering:
- Extensibility -- can define new elements, containers, attribute names
- Structure -- a DTD can constrain the information model of a document
- Validation -- every document can be validated; also, well-formedness can establish conformance to the structure mandated by the DTD
XML includes extensible linking and style formatting also
“Node content must be left free to evolve.” [Tim Berners-Lee, 1991, “About Document Formats”]