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RE: firts and rdf:rest as functional property

From: Jeremy Carroll <jeremy@topquadrant.com>
Date: Wed, 18 Feb 2009 08:52:50 -0800
To: 'Reto Bachmann-Gmür' <reto.bachmann@trialox.org>, "'Semantic Web'" <semantic-web@w3.org>
Message-ID: <002601c991e9$56b1f340$0415d9c0$@com>

IIRC the lack of this being specified in RDF Semantics is because in the layered architecture such constraints belong in an OWL layer, and requiring this of RDF implementations was seen as unduly burdensome.
However, given the lack of use cases for irregular lists, it is permitted for implementations to be stricter than is required.

They MAY exclude interpretations of the collection vocabulary which violate the convention that the subject of a 'linked' collection of two-triple items of the form described above, ending with an item ending with rdf:nil, denotes a totally ordered sequence whose members are the denotations of the rdf:first values of the items, in the order got by tracing the rdf:rest properties from the subject to rdf:nil.

Given this, using irregular lists would be an interoperability bug in the making, but there is no requirement on implementations to warn about this.


> -----Original Message-----
> From: semantic-web-request@w3.org [mailto:semantic-web-request@w3.org] On
> Behalf Of Reto Bachmann-Gmür
> Sent: Wednesday, February 18, 2009 3:28 AM
> To: Semantic Web
> Subject: rdf:firts and rdf:rest as functional property
> >From the description of RDF collections in the primer I would consider
> rdf:first and rdf:rest as functional properties. However,
> http://www.w3.org/TR/rdf-schema/#ch_list says:
> >
> > Note: RDFS does not require that there be only one first element of a
> > list-like structure, or even that a list-like structure have a first
> > element.
> I understand that RDFS doesn't have the notion of functional properties,
> but it could nevertheless be specified specifically for rdf:first and
> rdf:rest.
> Especially since RDFS also states that:
> > A triple of the form:
> >
> > L rdf:rest rdf:nil
> >
> > states that L is an instance of rdf:List that has one item; that item
> > can be indicated using the rdf:first property
> I'm not sure if this means that the last element has exactly or at least
> one item. In any case to me this seems to be a rather weird
> special-casing of the last rdf:List in a structure.
> My questions:
> - Are there useful usages where an rdf:list has several distinct
> rdf:first and rdf:rest value?
> - Is it just not written that rdf:first and rdf:rest are functional
> (maybe due to some spec layering reasons) or is false to consider
> rdf:first and rdf:next as functional?
> Cheers,
> reto
Received on Wednesday, 18 February 2009 16:53:28 UTC

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