On Nov 24, 2013, at 5:50 AM, Michael Brunnbauer <brunni@xxxxxxxxxxxx> wrote: (01)
>
> Hello Pat, (02)
Hi Michael (03)
>
> On Sat, Nov 23, 2013 at 12:48:48PM -0800, Peter Yim wrote:
>> I will concede that the inference patterns
>>
>> aaa subProperty bbb .
>> bbb domain//range ccc .
>> |=
>> aaa domain//range ccc .
>>
>> are a reasonably intuitive idea which could be added as axioms,
>> although I can see ways in which it would be found puzzling by some
>> users (those who are used to thinking of domains and ranges as
>> attached to a class rather than to its extension.) But I have never
>> come across any application that needed it, and AFAIK it has never
>> been requested or even suggested by any RDF user.
>
> My tool RDF2RDB http://www.netestate.de/De/Loesungen/RDF2RDB produces this
> entailment on TBox level and also implements transitivity of subClassOf and
> subPropertyOf. The entailment that a property has a certain domain or range
> actually makes a difference to this application: Facts are copied
> into less tables if the corresponding property has known domains/ranges and
> the entailment may produce those domains/ranges.
>
> For example if we know that foaf:knows has domain foaf:person and we know
> that x a foaf:person and x a whatever:livingthing, the fact that
> x foaf:knows y is not needed in the context of whatever:livingthing
> (aka in the tables corresponding to whatever:livingthing). (04)
That is interesting, it amounts to a kind of negative entailment: "if I know
this, I don't need to record that". Which could indeed lead to some entailments
creating less work downstream. I confess I had not thought of mechanisms like
this when thinking about efficiency. (05)
>
> RDF2RDB is not a clean RDFS reasoner anyway as it also picks some properties
> and entailments from OWL. (06)
Yes. I think it is important to emphasise that an application can always use
'stronger' entailments if you want it to do so. We tried to emphasise this
point in the new version of the document (section 5.3 "The fact that an
inference is valid should not be understood as meaning that any RDF application
is obliged or required to make the inference. Similarly, the logical invalidity
of some RDF transformation or process does not mean that the process is
incorrect or prohibited. Nothing in this specification requires or prohibits
any particular operations on RDF graphs or sources. Entailment and validity are
concerned solely with establishing the conditions on such operations which
guarantee the preservation of truth. While logically invalid processes, which
do not follow valid entailments, are not prohibited, users should be aware that
they may be at risk of introducing falsehoods into true RDF data. Nevertheless,
particular uses of logically invalid processes may be justified and appropriate
for data processing under circumstances where truth can be ensured by other
means." ) (07)
>
> But when developing RDF2RDB, I assumed that the entailments above are mandated
> by RDFS and I had read the RDF 1.0 semantics document before - apparently
> not close enough. Section 7.3.1 and section 4.1 are quite clear.
>
> So if this stuff is missing in RDF 1.1, maybe some prominent warning about
> what is not entailed should be there. (08)
It is hard to know how to make prominent warnings about what is NOT entailed,
as so much is not entailed. Let me ask you, why did you assume that it was
entailed? (09)
Pat (010)
>
> Regards,
>
> Michael Brunnbauer
>
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