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Re: Use cases wrt Dataset proposal (UC 1.5, UC 5.2)

From: Alex Hall <alexhall@revelytix.com>
Date: Wed, 29 Feb 2012 10:44:19 -0500
Message-ID: <CAFq2bixF+bxUaymXDA88CgOb40DChSUGRYeUvJ=Gip3NXnnAow@mail.gmail.com>
To: Pat Hayes <phayes@ihmc.us>
Cc: Antoine Zimmermann <antoine.zimmermann@emse.fr>, RDF WG <public-rdf-wg@w3.org>
On Wed, Feb 29, 2012 at 10:27 AM, Pat Hayes <phayes@ihmc.us> wrote:

> On Feb 29, 2012, at 8:43 AM, Antoine Zimmermann wrote:
> > *Beware*: this is about design solutions using the dataset proposal as a
> whole. It is not strictly related to the semantics. It explains concretely
> how one could store things in a dataset, possibly entail new things
> according the dataset semantics of [2] and so on, such that eventually it
> addresses the use case. So it contains a number of things that applications
> should do to address the UCs, independently of the truth values of triples
> or "named" graphs.
> >
> >
> > UC 1.5: Exchanging the contents of RDF stores
> >
> > This is trivial. RDF stores mostly implement SPARQL datasets, so it
> suffices to have a serialisation syntax for datasets. It does not matter
> what the semantics is. TriG or N-Qauds will do.
> >
> >
> > UC 5.2: OWL's “Ontology Documents”
> >
> > Currently, OWL imports statement means that an OWL processor should
> fetch wathever document it founds when "accessing" the imported URI (using
> whatever protocol it needs, see [1]). This behaviour is independent of the
> formal semantics of OWL ontologies. It's an operation that must be done
> prior to any interpretation of the ontology.
> >
> > If multiple ontologies are stored in a dataset, it seems reasonable to
> use the import mechanism offline, where instead of a HTTP lookup, the
> system directly fetches from the corresponding "named" graph.
> Whoa. I dont think this is at all reasonable. This changes the meaning of
> owl:imports, in effect (or extends it in a new way). After all, the URIs
> used as labels in a datastore might *refer* to anything, and in particular,
> they might refer to a different ontology stored somewhere on the web
> identified by an http URI. So the meaning of an imports might change when
> the ontology containing it is put into a dataset and taken offline.

Scruffy implementer hat on... This is more or less what our ontology
management product (Knoodl) already does. If you load an ontology that
owl:imports some http URI, we don't go out and fetch the document from that
URI. Instead we ask you to map that URI to some ontology stored locally in
Knoodl. So we keep a mapping off to the side of imported ontology URI to
local graph label, and use that for an offline import mechanism whenever
you access an ontology that has an import.

There always seemed to be something vague and hand-wavy about how
owl:imports was defined (especially in OWL 1) so we didn't give much
thought to the underlying semantics. It would be great if, once the
semantics of datasets and graph URIs/labels are formalized, it supports
this use. In the end, it works and it seems to keep our users happy.


> At the very least, if we mandate this, then we need to clarify the
> semantic role of "label" URIs in datasets.
> Pat
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Received on Wednesday, 29 February 2012 15:45:16 UTC

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