- From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
- Date: Thu, 25 Feb 2016 17:06:38 -0800
- To: ross.horne@gmail.com
- Cc: Simon Spero <sesuncedu@gmail.com>, Semantic Web <semantic-web@w3.org>, Reto Gmür <reto@wymiwyg.com>, Alan Jeffrey <ajeffrey@bell-labs.com>
On 02/24/2016 08:42 PM, Ross Horne wrote: > Hi Peter, > > On 24 February 2016 at 22:39, Peter F. Patel-Schneider <pfpschneider@gmail.com > <mailto:pfpschneider@gmail.com>> wrote: > > My paper has a lot of discussion of schema.org <http://schema.org> domains > and ranges. The paper > does not refer much to s:rangeIncludes (or s:rangeIncludes) as these IRIs are > not part of schema.org <http://schema.org> per se. I view the discussion > of domains and ranges in > the paper as relatively complete. > > > I see. Your paper makes things much clearer, even if not official from > schema.org <http://schema.org>. In schema.org <http://schema.org> ranges are > already disjunctive. > > > One problem with domains and ranges in schema.org <http://schema.org> is > their behaviour when > extra domains and ranges are available. Constructs that are invalid in some > way without the extra domains and ranges are valid with them. This is, in some > sense, non-monotonic behaviour. > > > I like the way you carefully say "in some sense, non-monotonic behaviour". In > another sense, this is completely monotonic behaviour. In this other sense, > properties are contravariant (just as inputs to functions or data sent over a > channel). Thus to refine the type of a resource you strengthen the type, using > intersection for example; but for properties you do the opposite, you weaken > the type, using union for example. In this way, we can monotonically refine > the schema information to accommodate both new explicit type information and > new range triples. I used the qualifier to indicate that I meant in a logical sense. Perhaps I should have been more explicit. In a logical sense, and that's the one that should be used when looking at schema.org as logical information, schema.org domains and ranges are non-monotonic. Adding more input information results in fewer consequences. You can consider schema.org markup to be something other than logical information. This opens up a lot of possibilities in how you can treat schema.org markup. However, it opens up a lot possibilities in how you have to treat schema.org markup. > Despite many helpful pointers, I am still unconvinced from this thread that > there is practical rational behind the decision by the RDF Schema working > group to make property domains and ranges conjunctive rather than disjunctive. > The example given by AZ was unclear until he highlighted he was also > considering female lizards;) However, on the other hand, there are scenarios > where two people state that the range of a property is different type. E.g., > in DBpedia, dbp:subdivisionName is sometimes used with range int and other > times used with URI dbp:Place: > > dbpedia:Rockmart,_Georgia dbp:subdivisionName 1872 . > dbpedia:Rockmart,_Georgia dbp:subdivisionName dbpedia:Polk_County,_Georgia . > > This can easily happen with more than one person contributing data, as > intended on the Web of Data. However, if both authors separately contributed > respective schema information for the range, then under the conjunctive > semantics any triple in which dbp:subdivisionName appears as the property is > inconsistent. In contrast, under a disjunctive semantics both contributors > datasets can be used together -- even without prior coordination -- as > expected on the Web of Data. I am possibly opening a Pandora box here, by > using an int along with a URI in this example; but similar weaker examples > using URIs only and resulting in nonsensical conjunctions instead of full > blown inconsistencies can be constructed. One problem with this approach is when you want to use the information. You can't count on the fillers of a property to belong to the class (or datatype) that you expected them to. How, for example is an application supposed to process subdivision information when it could be a place, or an int, or a string, or a person, or ... anything? > > Using owl:unionOf, the above problem can be resolved, but only with concious > coordination between the two contributors and also by stepping slightly out of > RDF Schema. > > Of course, a standard is a standard, so I should say no more. However, if > anyone does have a strong either practical or model theoretic case for the > conjunctive handling of domains and ranges in the RDF Schema spec then I would > be most interested to hear at any point. The way to treat RDF information has been a subject of debate from the beginning. The current W3C standards generally treat RDF triples as independent logical axioms. Using this treatment biases how the rest of RDF is set up. > > Kind regards, > > Ross > peter
Received on Friday, 26 February 2016 01:07:10 UTC