On 10/11/13 13:06, Jonathan Lang wrote: > On Nov 10, 2013, at 2:33 AM, Markus Krötzsch <mar...@semantic-mediawiki.org> > wrote: > >> On 10/11/13 10:43, Niklas Laxström wrote: >>> What is OWA? >> >> John refers to the "Open World Assumption". This is an informal concept >> used in knowledge representation to describe the assumption that >> statements that are not made are "unknown" rather than "false". This is >> contrasted with the "Closed World Assumption" that is common in >> databases, where we assume that unspecified information is false. > > -snip- > > Thank you for that; it was incredibly informative. If you don’t mind, I have > a followup question of my own: > >> What John refers to is that SMW assumes a default type for properties >> (Page). Therefore, the input behaviour is not monotonic: if you specify >> another type later, then this will make the formerly true type Page >> false. However, this is not a "violation" of the OWA. Wikitext is just a >> surface syntax and not the internal knowledge model of SMW. Wikitext can >> never be monotonic: for example, if a page contains >> "[[someprop::somevalue]]" and you add an input character "X" to obtain >> "[X[someprop::somevaue]]" then SMW will no longer contain the fact. >> Parser functions, templates, comments, etc. will all lead to similar >> effects. > > I think I understand what you’re saying here. What I’d like to know is > whether any of this applies to the equivalency that exists (or is that past > tense? I’m a bit behind the development curve right now) between OWL classes > and MW Categories? That is, aren’t we making potentially unwarranted > assumptions about the semantic significance of a Category when we assume that > all Categories are classes, and vice versa?
That depends on how you use MW classes. Instances of OWL classes are propagated up the hierarchy: if A instanceOf B and B subclassOf C then A instanceOf C). MW classes do not behave like this. If one uses MW classes in a way for which this behaviour is not useful, then OWL classes are not a good way to capture this. In this case, the OWL export that SMW generates is of limited utility. Queries in SMW also interpret the category hierarchy in the same way as OWL, but this can be switched off if it does not work for you. Assuming that all MW categories in all wikis are intended to be used like OWL classes would certainly be an unwarranted assumption. SMW does not make that assumption, but if you install SMW on a wiki with its default configuration, then you choose this as your preferred way of treating categories. Note that the previous paragraph speaks mainly about how a system behaves and whether this is desired or not. This is the only level on which we can discuss the relationship of MW and OWL -- considering them as pieces of technology that do something for the user. In particular, MW does not have a specified semantics (or even a formal syntax!), since it is not a format meant to exchange information across applications. So there is no right or wrong way of using MW categories, and one cannot say that they are generally compatible or generally incompatible with OWL. Cheers, Markus ------------------------------------------------------------------------------ November Webinars for C, C++, Fortran Developers Accelerate application performance with scalable programming models. Explore techniques for threading, error checking, porting, and tuning. Get the most from the latest Intel processors and coprocessors. See abstracts and register http://pubads.g.doubleclick.net/gampad/clk?id=60136231&iu=/4140/ostg.clktrk _______________________________________________ Semediawiki-devel mailing list Semediawiki-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/semediawiki-devel
