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Bullard, Claude L (Len) wrote: > Well, DUH! If a semantic web means is a namespace URI points > to a schema somewhere, I am completely underwhelmed. RDF schemas are intended to complement not replace XML schemas. An RDF schema defines a semantic hierarchy, or network, of element names. The URI created by concatenating the namespace URI to the element name identifies an RDF Schema Class to which the instance belongs, or may identifiy an RDF Schema Property. This is totally different than syntactic level constraints placed by a DTD or XML Schema on an XML document. An RDF schema defines a fragment of a semantic network which includes instances of the classes and properties. The semantic web is at its simplest a network of nodes and arcs (properties) which use URIs for both node and arc names. The namespace mechanism is simply the mechanism by which XML element names are translated into URIs identifying nodes and arcs in the 'semantic web'. The XML model defines a node labelled directed graph. In this model, arcs or edges have the type "element" "attribute" "CDATA section" "comment" etc. The RDF model defines an edge labelled directed graph, for example arcs may be labelled "color", "type.of.cheese" "type.of.sauce" "topping". This may not seem a radical difference but understand that software which makes inferences regarding the properties of a pizza, as represented in an RDF graph, may be totally unconcerned about whether the "type.of.cheese" is an attribute or an element and whether this property is serialized before or after the "type.of.sauce" property. Jonathan Borden The Open Healthcare Group http://www.openhealth.org
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