I'm a newcomer here, so it's possible that this has been discussed to death and I simply haven't found the relevant topics (although I _have_ looked). Bearing that in mind:
I ran across the following statement on the SMW Help pages (in particular, < http://semantic-mediawiki.org/wiki/Help:RDF_export#Categories >): "There are many usages of MediaWiki categories that conflict with these semantics. For example, the article Urban decay might be in category Cities, but it is not a city. And Category:City museums might be in category Cities, but city museums are not cities." This strikes me as being a potentially serious problem, especially when it comes to using an external ontology manager to do further analysis on the appropriate SMW articles. Conversely, it was indicated elsewhere that these conflicting usages are actually quite desirable as far as wikis are concerned, since categories are supposed to group together articles of common interest. >From the above, it seems to me that Categories are _not_ the appropriate equivalent to OWL/RDF classes. That is, the presence of a '[[Category:xxx]]' annotation in an article should not automatically map to an rdf:type element; nor should its presence in a Category page automatically map to an rdfs:subClassOf element. Bear with me, please. OTOH, I do agree that whatever annotation does map to rdf:type and rdfs:subClassOf should be something that causes the article or category in question to be added to a category. Here's what I'm proposing: 1. Add a new Property Type: namely, Type:Category. Like Type:Page, Properties of Type:Category define a relation between two pages. Unlike Type:Page, the page being pointed to is always a Category; and including this Property on a page implicitly categorizes it. By annotating pages with properties of this type, it becomes possible to distinguish between different reasons for including the page in the category. 2. Add a new special property: 'Class'. Property:Class has type Category; additionally, only categorization by means of Property:Class would map to rdf:type and rdfs:subClassOf; all other means of categorization (including the traditional '[[Category:foo]]' annotation) would map to owl:ObjectProperty. I'd also add a special property 'Category'. Categorizing through it would be identical to categorizing by the traditional mechanism: that is, '[[Category::foo]]' would be completely interchangeable with '[[Category:foo]]'. But this isn't strictly necessary; it's merely one way that you might ensure that you have a way of mapping '[[Category:foo]]' to an owl:ObjectProperty element. -- The main downside that I see to this proposal is that semantic wikis that adopt it would have to be thoroughly reviewed in terms of their category annotations. OTOH, the only alternatives that I see would be for a semantic wiki to insist that Categories only be used to represent 'is-a' relationships, or for the semantic wiki to ignore the issue. (Technically, you could reverse my proposal by providing a special Property that categorizes the page without establishing a class/instance-or-subclass relationship when exported; but this is essentially the same solution, changing only the "burden of proof", as it were.) It's possible for either of these to be viable solutions: a wiki that's built entirely around a given vocabulary can get away with mandating that all articles in a category must be instances of its class, and an open-ended wiki such as Wikipedia may not encounter this issue often enough to warrant the amount of work that would be needed to fix the problem. With this in mind, it's entirely possible that I'm proposing an SMW Extension, rather than an upgrade. That way, those wikis that want to implement this could, while those that don't want to bother with it don't have to. Thoughts? -- Jonathan "Dataweaver" Lang ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Semediawiki-devel mailing list Semediawiki-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/semediawiki-devel
