[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Semantic Web permathread, iteration n+1 (was Re:
Robert Koberg wrote: > Thomas B. Passin wrote: >> In RDF, a Property is a kind of Resource, and you can in fact make >> statements about it. However, apparently, this kind of practice >> prevents many kinds of logical reasoners (or maybe all, I am not >> expert enough to know) from being "sound" and /or "complete", so most >> of the restricted logics (like various forms of Description Logics) >> restrict the kinds of constraints you can place on properties (which >> is in effect restricting what you can say about them). The goal of >> such restrictions is to make sure that a reasoner can complete any >> assignment in a reasonable time (such a polynomial time as opposed to, >> say, exponential) and be sure that any answer is correct. > > > Doesn't this represent a flaw somewhere in RDF? > No, RDF itself does not retrict you from making statements about any "resource", including a property. Restrictions on various subsets of full first order logic (like OWL, which can be considered to be a subset) are usually put in place to make reasoning tasks more tractable. > Why are the examples in RDF of things that do not correspond to > hierarchies (unless striping (or perhaps more semantically, 'grouping') > is used)? Simplistic examples of things that will never have a hierarchy > do not help. Because the RDF model is not inherently hierarchical, although you can represent hierarchies. Subgraphs are more natural ways to look at RDF groupings, and a hierarchy is one kind of subgraph. Here is one example of a hierarchy root child1 subchild1a subchild1b child2 In rdf, how you do this may depend on whether the order within any level is important. If it is not, then in a striped format - root hasChild child1 has Child subchild1a subchild1b child2 If order is important, using rdf:parseType='Collection' causes the processor to produce something eqivalent to this - root rdf:first child1 rdf:first subchild1a rdf:rest (something untyped) rdf:first subchild1b rdf:rest rdf:nil rdf:rest (something untyped) rdf:first child2 rdf:rest rdf:nil The addition of the "nil" term makes this kind of list non-extendable (there are other list idioms that can be extended), which can be good if you don't want someone else claiming that there are more list items than you put in. Cheers, Tom P -- Thomas B. Passin Explorer's Guide the the Semantic Web (Manning Books) http://www.manning.com/catalog/view.php?book=passin
|
PURCHASE STYLUS STUDIO ONLINE TODAY!Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced! Download The World's Best XML IDE!Accelerate XML development with our award-winning XML IDE - Download a free trial today! Subscribe in XML format
|