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Re: A proposal for a simplification of the annotations subsystem

From: Ivan Herman <ivan@w3.org>
Date: Tue, 18 Nov 2008 08:47:16 +0100
Message-ID: <49227304.1000307@w3.org>
To: Boris Motik <boris.motik@comlab.ox.ac.uk>
CC: 'W3C OWL Working Group' <public-owl-wg@w3.org>
Boris,

I will not be at the phone meeting, so: I like what I read:-) I am all
for a simplification and this looks like one...

You write that it affects the RDF Mapping; I presume it is the RDF->FS
that is affected and not the other way round, right?

Thanks

Ivan

Boris Motik wrote:
> Hello,
> 
> I know it is quite late in the day, but while I was implementing the resolution from the last F2F, I've noticed several
> opportunities for simplification of the current spec. Please understand that
> 
> - this would be just a simplification/clean-up of the structural specification and it does not incur any fundamental changes
> regarding the actual capabilities of annotations, and
> 
> - it would affect only the structural specification, the RDF Mapping, and the XML Syntax documents.
> 
> 
> Problem
> ----------------------
> 
> Currently, in the metamodel of OWL 2 we have three classes for various types of annotations:
> 
> - AnnotationByURI,
> - AnnotationByLiteral, and
> - AnnotationByAnonymousIndividual.
> 
> This is quite unwieldy.
> 
> Furthermore, the metamodel of OWL 2 currently contains two different axioms for associating annotations with things:
> 
> - URIAnnotation and
> - AnonymousIndividualAnnotation.
> 
> Again, quite unwieldy.
> 
> Another problem is that, while it would be intuitive to expect the structure of annotations to be similar to assertions, this is not
> the case. A property assertion consists of two individuals and a property, and it specifies just one fact. In contrast, a single
> annotation axiom specifies a set of annotations for an individual, and essentially specifies more than one fact. Consider the
> following examples:
> 
> (1) PropertyAssertion( P i1 i2 )
> (2) URIAnnotation( i1 Annotation( AP1 v1 ) Annotation( AP2 v2) )
> 
> In fact latter syntax is quite unwieldy, because it uses the terminal 'Annotation' quite often.
> 
> Because of this, round-tripping of annotations through RDF is not possible. If you wrote (2) as two separate annotations, serialized
> the ontology into RDF, and read everything back, your two annotation axioms would be merged into one axiom (2).
> 
> 
> Proposal Outline
> ----------------------
> 
> The proposal consists of two changes.
> 
> The first problem could be addressed by introducing a class called, say, AnnotationValue, as a superclass of URI, Literal, and
> AnonymousIndividual. Then, we could replace three types of annotations with just one type that refers to AnnotationValue.
> 
> The second problem could be addressed by breaking up axioms of the form (2) into several axioms, each of which provides just one
> annotation value. Thus, instead of (2), we would write something like this:
> 
> (3) Annotation( AP1 i1 v1 )
> (4) Annotation( AP1 i2 v2 )
> 
> This would actually bring the structural specification closer to RDF.
> 
> 
> Concrete Proposal for the Grammar
> ----------------------
> 
> Here is what the grammar of the FS might look like:
> 
> AnnotationSubject := URI | AnonymousIndividual
> AnnotationValue := URI | AnonymousIndividual | Literal
> Annotation := 'Annotation' '(' axiomAnnotations AnnotationSubject AnnotationValue ')'
> 
> axiomAnnotations := { StatementAnnotation }
> StatementAnnotation := 'StatementAnnotation' '('
>     { StatementAnnotation } AnnotationProperty AnnotationValue ')'
> AnnotationAxiom := Annotation | SubAnnotationPropertyOf |
>     AnnotationPropertyDomain | AnnotationPropertyRange
> 
> Here is a summary of the grammar changes:
> 
> - What is currently the Annotation nonterminal would become StatementAnnotation.
> - What is currently URIAnnotation and AnonymousIndividualAnnotation would become Annotation.
> 
> I believe that the result would be a much simpler metamodel and a much nicer syntax. I could enact this change really quickly.
> 
> 
> 
> Please let me know how you feel about this. Could we perhaps discuss this at the next teleconf?
> 
> Regards,
> 
> 	Boris
> 
> 

-- 

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf


Received on Tuesday, 18 November 2008 07:47:54 GMT

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