On 6/6/11 9:59 AM, Thomas Bandholtz wrote:
For me, schema.org is just another schema. As the three major seach
engines agree on it, it will become a de-facto standard regardless to
wether we like it or not.
Obviously, they decided not to re-use anything as they are sure enough
they will be re-used instead.
What you bring up is called polymorphy in the OO world: Any instance may
be instance of multiple classes. I have a case where the domain experts
are talking about a thesaurus, so everthing is a skos:Concept.
But they have also place names and events.
So far, each place name is label of a skos:Concept. But we also have the
more specific Geonames Ontology, so the place name is as well
gn:officialName which implies that the same instance now has also type
gn:Feature (which is subclass of wgs84:SpatialThing, so the instance is
as well a wgs84:SpatialThing).
Now we have one more player in the open schema world:
the same instance will now become a schema:Place instance as well.
So what?
As far as these schemas are not inconsistent with one another, there is
absolutely no problem. If there are some contradictions, the reasoner
will hopefully detect them and give us a chance to align the schemas
with a good reason.
What is the "purpose" of such multiple class assignment?
Any agent searching the LOD cloud for skos:Concept instances will find
my instance, and the same applies to those agents searching for
gn:Feature or schema:Place instances.
If your instance is not found, you may as well delete it ;-)
I used to dream about schema alignment and re-use for decades, but I
have come to the conclusion: schema diversity is just like
bio-diversity. We do not have to overcome it, it is a protected asset!
Yep ++
KIngsley
Best regards,
Thomas
Am 05.06.2011 13:28, schrieb Hugh Glaser:
Interesting question.
As an an engineer, I was trying to work out if the schema was fit for purpose.
Of course, I was assuming that we agreed on what the purpose was, but that was
a mistake, as it usually is.
I thought that the purpose was that I would have a schema I could then use in
my RDF, that would have a simple correspondence with schemas.org (so I stood a
chance of moving between them), while enabling me to do my Linked Data goodness
(importantly conforming to the first principle).
In particular, I did not think that we were trying to capture the exact meaning
of what they (Schema.org) say.
So my fit for purpose would have (at least):
1) Will the resultant RDF be useable as Linked Data?
2) Can I move between the two notations without loss of (important) information?
The following from Schema.org seems very relevant in the second of these
"Conformance
While we would like all the markup we get to follow the schema, in practice, we expect a lot
of data that does not. We expect schema.org properties to be used with new types. We also
expect that often, where we expect a property value of type Person, Place, Organization or
some other subClassOf Thing, we will get a text string. In the spirit of "some data is
better than none", we will accept this markup and do the best we can."
So what can the RDFS respond to this, with particular reference to (my) purpose
(2)?
As always we must ask what is the role of the schema.
It clearly can't be to police an acceptance of valid RDF documents that have
come from Schema.org - it would reject many things that will become acceptable
to Schema.org.
It clearly can't be to police the publication of RDF documents on their way to
Schema.org - it would restrict too much.
It may be useful to provide inference in a RDF store with schema.rdfs.org RDF
in it.
Essentially, it means not only dropping all the range restrictions, but even
the domains as well, if it is to be fit for (my) purpose (2).
But it then becomes less useful for (my) purpose (1).
Indicating useful restrictions is a good thing to do, to help me get my RDF
right, and help me work out what is in a schema.rdfs.org RDF store, and even
give me more useful inference in the store.
It is just that such use directly conflicts with being useful as a bridge with
Schemas.org.
How to square the circle?
To be useful for the future development of Schemas.org, the more I look the
more I think just dropping all domain and range is the only way forward (does
that go too far for you, Pat? :-) )
However, the schema.rdfs.org does tell me a lot of useful stuff with the
restrictions - is it really the case that more than one description is useful?
That would be horrible or would it?
I suspect that I may need to don a flameproof suit here, as I tread into well
worn paths of knowledge acquisition, but never mind, it's Sunday morning and
raining outside :-)
Best
Hugh
On 5 Jun 2011, at 07:37, Thomas Bandholtz wrote:
Am 04.06.2011 17:35, schrieb Pat Hayes:
Far as I can see, one could simply delete every range-string triple. Nothing
would break in the RDFS by doing this, and AFIKS nothing is gained from having
these range assertions.
Deleting every range assertion would not express what they want to say:
"many properties have 'expected types'. This means that the value of the
property can itself be an embedded item ... But this is not a
requirement—it's fine to include just regular
text or a URL." [1]
They do not expect just anything, but a certain type or a literal
(denoting an "informal" instance of this type).
Sounds like
schema:someProperty rdfs:range [ owl:unionOf (schema:Thing rdfs:Literal ) ];
What funny kind of OWL flavor or profile might this be?
Note that they do not use owl:ObjectProperty nor owl:DatatypeProperty
but simply rdf:Property, so it might be just fine. Good old RDFS!
Some comments from the OWL police?
Thomas
[1] http://schema.org/docs/gs.html#schemaorg_expected
Pat
On Jun 4, 2011, at 4:39 AM, Hugh Glaser wrote:
Sure does rock.
As you know, I never venture into ontology definition, to avoid displaying my
ignorance, but now and then... :-)
Suggestion:
The RDFS will (I think!) perpetuate the classic problem (being a natural
translation), in that there are lots of range strings.
For example:
schema:currenciesAccepted a rdf:Property;
rdfs:label "Currencies Accepted"@en;
rdfs:comment "The currency accepted (in ISO 4217 currency format)."@en;
rdfs:domain schema:LocalBusiness;
rdfs:range xsd:string;
rdfs:isDefinedBy<http://schema.org/currenciesAccepted>;
.
and
schema:headline a rdf:Property;
rdfs:label "Headline"@en;
rdfs:comment "Headline of the article"@en;
rdfs:domain schema:CreativeWork;
rdfs:range xsd:string;
rdfs:isDefinedBy<http://schema.org/headline>;
.
And even productID
I count 53 "rdfs:range xsd:string" and 8 "rdfs:range [ owl:unionOf (xsd:decimal
xsd:string) ]" of this kind.
As I say, I think that means that to conform, I can't have a Resource as Range.
So it is institutionalising a Bad Thing, simply because schema.org says that, for example,
"productID" is "text".
Of course, people who use http://schema.rdfs.org/ probably will use Resources
for places, currencies, etc, (as they should) so maybe the RDFS needs to
reflect this?
Won't try and suggest...
Best
Hugh
On 3 Jun 2011, at 22:06, Michael Hausenblas wrote:
http://schema.rdfs.org
... is now available - we're sorry for the delay ;)
Cheers,
Michael
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