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Re: rdf:Property used as rdf:object in a triple

From: Frank Manola <fmanola@acm.org>
Date: Sun, 5 Nov 2006 12:32:37 -0500
Message-Id: <93E9E0B8-85EE-4466-B406-9302C9C4D839@acm.org>
Cc: "'Leo Sauermann'" <leo.sauermann@dfki.de>, "'Paul Gearon'" <gearon@ieee.org>, "'SW-forum'" <semantic-web@w3.org>, "'Chris Wilper'" <cwilper@cs.cornell.edu>
To: Hans Teijgeler <hans.teijgeler@quicknet.nl>


Technically there is more than one kind of reification.  You don't  
necessarily want to use "RDF reification" (talking about individual  
statements, and using the RDF reification vocabulary), but you do, I  
think, want to use the generic idea of "reification" in information  
modeling (you can Google it).  Specifically, the examples you've  
cited involve treating connections and relationships between John and  
Jane as things you want to make statements about (or "objects in the  
domain of discourse", if you're reading a logic text), and that's a  
form of reification (whether you use the RDF concept of reification  
or not).  The thing that often causes some difficulty is this:  any  
data model (object model, information model, etc.;  predicate logic  
is an example) provides a way to describe "objects" (entities,  
things, ...) and attributes of/relationships between those objects.   
RDF provides "resources" to represent (actually denote) things, and  
statements to represent attributes and relationships.  Your job as an  
information modeler is to map the objects, attributes, and  
relationships you want to describe in your application to the  
objects, attributes, and relationships provided by the data model.   
But those aren't always in one-to-one correspondence.  Here, for  
example, what you think of as a relationship in the application (like  
the relationship between John and Jane) needs to be modeled as an  
object (thing) in the data model, because you want to make statements  
about it (describe its attributes) and, at least in RDF (and, in  
fact, in most data models), the things you make statements about have  
to be objects (in RDF, resources).


On Nov 5, 2006, at 11:33 AM, Hans Teijgeler wrote:

> Hi Leo,
> In your 1st link I read:
> It may be natural to think of RDF reification when representing n- 
> ary relations. We do not want to use the RDF reification vocabulary  
> to represent n-ary relations in general for the following reasons.  
> The RDF reification vocabulary is designed to talk about statements— 
> individuals that are instances of rdf:Statement. A statement is a  
> object, predicate, subject triple and reification in RDF is used to  
> put additional information about this triple. This information may  
> include the source of the information in the triple, for example.  
> In n-ary relations, however, additional arguments in the relation  
> do not usually characterize the statement but rather provide  
> additional information about the relation instance itself. Thus, it  
> is more natural to talk about instances of a diagnosis relation or  
> a purchase rather than about a statement. In the use cases that we  
> discussed in the note, the intent is to talk about instances of a  
> relation, not about statements about such instances.
> In your 2nd link I read in chapter 4.3:
> For one thing, it is important to note that in the conventional use  
> of reification, the subject of the reification triples is assumed  
> to identify a particular instance of a triple in a particular RDF  
> document, rather than some arbitrary triple having the same  
> subject, predicate, and object. . . . . . Thus, to fully support  
> this convention, there needs to be some means of associating the  
> subject of the reification triples with an individual triple in  
> some document. However, RDF provides no way to do this.
> This does not increase my enthousiasm for reification.
> Besides that I still see no sign that one can generalize this in an  
> OWL schema for validation purposes.
> Regards,
> Hans
> From: Leo Sauermann [mailto:leo.sauermann@dfki.de]
> Sent: Sunday, November 05, 2006 15:55
> To: Hans Teijgeler
> Cc: 'Paul Gearon'; 'SW-forum'; 'Chris Wilper'; Manola, Frank
> Subject: Re: rdf:Property used as rdf:object in a triple
> Hi Hans,
> have you looked into Reification and did you try it out for your  
> problem?
> checkout reification, it will do what you need.
> http://www.w3.org/TR/swbp-n-aryRelations/#RDFReification
> http://www.w3.org/TR/2004/REC-rdf-primer-20040210/#reification
> Or read this article, which explains why Reification may be what  
> you may need:
> or if you should go for indivivduals
> http://www.w3.org/TR/swbp-n-aryRelations/
> greetings
> Leo
> Es begab sich aber da Hans Teijgeler zur rechten Zeit 05.11.2006  
> 10:47 folgendes schrieb:
>> Hi Paul,
>> Thanks for your response! (and thanks as well to Chris and Frank).
>> Let me explain this with a simple example:
>> John isInvolvedWith Jane
>> Jane's father Pete givesApprovalTo that relationship
>> This means that the isInvolvedWith relationship is the rdf:object  
>> of the predicate 'givesApprovalTo'.
>> We then also want to represent the owl:Restriction that Fathers  
>> approve such relationships of their daughters (granted, it's a bit  
>> old-fashioned, but it's just an example).
>> This example is not rare. Another one is:
>> Nozzle N1 isWeldedTo Vessel V1
>> that welded connection isInspectedBy John
>> I guess that I should start using reification, but quite honestly  
>> I am too dumb to understand the text in [1]
>> [1] http://www.w3.org/TR/rdf-mt/#Reif
>> Is reification at all possible in an OWL environment? It seems not  
>> to be the case.
>> Mind you, we define "templates" with Restrictions in OWL that will  
>> be used to validate the zillions of instances of those templates  
>> in RDF. So for example we define, using 15926 model lingo, a  
>> template for DirectConnection of two PossibleIndividuals, and make  
>> sure, using owl:Restrictions, that any instance of that template  
>> has an instance of PossibleIndividual at both sides. These  
>> templates can be specialized by onProperty restrictions to, for  
>> example, a template for welded connections that can only be  
>> between instances of PossibleIndividual that can be welded at all.
>> I hope I haven't made this too complex :-)
>> Regards,
>> Hans
>> ____________________
>> OntoConsult
>> Hans Teijgeler
>> ISO 15926 specialist
>> Netherlands
>> +31-72-509 2005
>> www.InfowebML.ws
>> hans.teijgeler@quicknet.nl
>> From: Paul Gearon [mailto:gearon@ieee.org]
>> Sent: Saturday, November 04, 2006 23:56
>> To: Hans Teijgeler
>> Cc: SW-forum
>> Subject: Re: rdf:Property used as rdf:object in a triple
>> On Nov 4, 2006, at 6:25 AM, Hans Teijgeler wrote:
>>> Folks,
>>> rdf:Property is a subClassOf rdfs:Resource, so syntactically a  
>>> property could be the rdf:object of a triple.
>>> My question is, whether or not there is something against doing  
>>> that from a semantics/reasoning point of view.
>>> Can anybody shed some light on this?
>> There's certainly no rule against it.  Reification requires it.   
>> So does rdfs:subPropertyOf.
>> As for semantics... you can get away with a lot in RDF.  But if  
>> you want to keep things as valid OWL-Lite or OWL-DL then you have  
>> to be more careful, as properties are treated a little differently  
>> to other resources.  Properties only start getting back the  
>> "privileges" of other types of resources (like classes) when you  
>> get up to OWL-Full.
>> Paul
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> -- ____________________________________________________ DI Leo  
> Sauermann http://www.dfki.de/~sauermann DFKI GmbH P.O. Box 2080  
> Fon: +49 631 205-3503 67608 Kaiserslautern Fax: +49 631 205-3472  
> Germany Mail: leo.sauermann@dfki.de  
> ____________________________________________________ 
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Received on Sunday, 5 November 2006 17:32:52 UTC

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