Re: How do you explore a SPARQL Endpoint?

Hi Pavel

Maybe what you are missing is that RDF data, by design, do not need a
schema. Since the very notion of schema for RDF data has no meaning at all,
and the absence of schema is a bit frightening, people tend to give it a
lot of possible meanings, depending on your closed world or open world
assumption, otherwise said if the "schema" will be used for some kind of
inference or validation. The use of "Schema" in RDFS has done nothing to
clarify this, and the use of "Ontology" in OWL added a layer of confusion.
I tend to say "vocabulary" to name the set of types and predicates used by
a dataset (like in Linked Open Vocabularies), which is a minimal commitment
to how it is considered by the dataset owner, bearing in mind that this
"vocabulary" is generally a mix of imported terms from SKOS, FOAF, Dublin
Core ... and home-made ones. Which is completely OK with the spirit of RDF.

The brand new LDOM [1] or whatever it ends up to be named at the end of the
day might clarify the situation, or muddle those waters a bit more :)

[1] http://spinrdf.org/ldomprimer.html

2015-01-23 10:37 GMT+01:00 Pavel Klinov <pavel.klinov@uni-ulm.de>:

> Alright, so this isn't an answer and I might be saying something
> totally silly (since I'm not a Linked Data person, really).
>
> If I re-phrase this question as the following: "how do I extract a
> schema from a SPARQL endpoint?", then it seems to pop up quite often
> (see, e.g., [1]). I understand that the original question is a bit
> more general but it's fair to say that knowing the schema is a huge
> help for writing meaningful queries.
>
> As an outsider, I'm quite surprised that there's still no commonly
> accepted (i'm avoiding "standard" here) way of doing this. People
> either hope that something like VoID or LOV vocabularies are being
> used, or use 3-party tools, or write all sorts of ad hoc SPARQL
> queries themselves, looking for types, object properties,
> domains/ranges etc-etc. There are also papers written on this subject.
>
> At the same time, the database engines which host datasets often (not
> always) manage the schema separately from the data. There're good
> reasons for that. One reason, for example, is to be able to support
> basic reasoning over the data, or integrity validation. Just because
> in RDF the schema language and the data language are the same, so
> schema and data triples can be interleaved, it need not (and often
> not) be managed that way.
>
> Yet, there's no standard way of requesting the schema from the
> endpoint, and I don't quite understand why. There's the SPARQL 1.1
> Service Description, which could, in theory, cover it, but it doesn't.
> Servicing such schema extraction requests doesn't have to be mandatory
> so the endpoints which don't have their schemas right there don't have
> to sift through the data. Also, schemas are typically quite small.
>
> I guess there's some problem with this which I'm missing...
>
> Thanks,
> Pavel
>
> [1]
> http://answers.semanticweb.com/questions/25696/extract-ontology-schema-for-a-given-sparql-endpoint-data-set
>
> On Thu, Jan 22, 2015 at 3:09 PM, Juan Sequeda <juanfederico@gmail.com>
> wrote:
> > Assume you are given a URL for a SPARQL endpoint. You have no idea what
> data
> > is being exposed.
> >
> > What do you do to explore that endpoint? What queries do you write?
> >
> > Juan Sequeda
> > +1-575-SEQ-UEDA
> > www.juansequeda.com
>
>


-- 

*Bernard Vatant*
Vocabularies & Data Engineering
Tel :  + 33 (0)9 71 48 84 59
Skype : bernard.vatant
http://google.com/+BernardVatant
--------------------------------------------------------
*Mondeca*
35 boulevard de Strasbourg 75010 Paris
www.mondeca.com
Follow us on Twitter : @mondecanews <http://twitter.com/#%21/mondecanews>
----------------------------------------------------------