Abstract

This thesis is about relations between schema languages for XML. A schema language is a formal definition of the syntax of an XML language and is used to check validity of a given XML document. There exists a variety of schema languages mainly developed around 2000. During the last six years some of the languages have matured and become either W3C or ISO standards, some have stabilized and some have vanished. Most of the languages have been stable in terms of language features during the last three years. Due to the stability of the schema languages, it is a good moment in time to take a step back and try to see the overall perspective of schema languages; for schema language designers to learn from the existing experiences and for schema language users to learn the strengths and weaknesses of the individual languages and so be better qualified the choose the right language for a given application. Revealing relations between six state of the art schema languages for XML, DTD, XML Schema, Schematron, DSD2, RELAX NG, and Summary Graphs, gives a good insight into the various perspectives of schema languages. The relations will be revealed using a twofold approach: first, we present a thorough feature-based comparison of schema languages and second, we present and investigate translations between the schema languages. This strategy gives us a strong basis from which we can point out the strengths and weaknesses of each language and conclude that the all-optimal schema language has yet to come.

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