Re: Schemata are not just constraints [was: "RDF + Topic Maps" = TheFutu
Eric van der Vlist wrote: > Jonathan, > > Jonathan Borden wrote: > > > > As DTDs and XML Schemata provide syntactic constraints, RDF Schemata provide > > semantic constraints (which for the purposes of this discussion is defined > > as placing constrainsts on arcs and nodes in a directed graph). So it is > > true that RDF Schema provides no more than a constraint mechanism, but I > > offer that this is precisely how ontologies are built. > > Even if sometimes I'd wish they are only this, I think that it's quite > limitative to restrict schemata (either syntaxic or semantic) to a set > of constraints. Please don't equate the term "provide constraints" to a stating that schemata are *restricted* to a set of constraints. A schema has two broad functions: 1) contraints 2) transforms (e.g. attribute defaulting) (if this isn't clear see Schematron!) Yet formally one might consider all constraints a type of transform, one that returns either 'true' or 'false' depending on the input. In any case it remains useful to consider schemata as providing constraints. Similarly one can formally define a transform given input and output constraints. So the two are inextricably intertwined. Jonathan Borden The Open Healthcare Group http://www.openhealth.org
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