Hi Christopher,
that is a good tipp. So in the future we would let them point to the
wkdb (wikidatadbpedia) identifiers:
<http://dbpedia.org/resource/Berlin> cidoc:preferredIdentifier
<http://wikidata.dbpedia.org/resource/Q64> .
what is the exact URL? and what is the difference to rdfs:definedBy
Sebastian
On 02.06.2016 04:43, Christopher Johnson wrote:
Hi,
Interesting discussion. One point that I do not think has been
evaluated here is the time, location and context components of a
statement. The assignment of an identifier is simply a statement made
about a concept that instantiates it as an entity. That statement is
bound to a time, location and context and the notions of persistence
and uniqueness are interpretations from that singular point of view.
In a modal reality, an infinite set of identifiers exists for any
given concept. The imposition of a uniqueness constraint on an
identity is decidable only within a well-known (and highly
administered) domain. CIDOC has a property called "P48 has preferred
identifier" with an owl:Restriction maxCardinality of "1".
This seems to be a reasonable solution to the question of
identifiers. Many identifiers can exist (and usually do), but there
can be only one "preferred identifier" for a resource in a given ontology.
Cheers,
Christopher
On 1 June 2016 at 21:53, Markus Kroetzsch
<markus.kroetz...@tu-dresden.de
<mailto:markus.kroetz...@tu-dresden.de>> wrote:
Hi Sebastian,
I'll try to clarify further. This really is a tricky topic and maybe
more than an email thread is needed to explain this. If you want
to dive
into the details, you may want to check out some textbooks to get
started (Abiteboul et al. would be the standard intro to database
theory
and Relational Algebra; for FOL there are many choices, but there
is no
DL-specific textbook; there are some good DL tutorials, however, that
may be useful). I don't know of a good reference that explains the
differences that are causing confusion here.
On 01.06.2016 17:03, Sebastian Hellmann wrote:
> Hi Markus,
>
> On 01.06.2016 14:49, Markus Kroetzsch wrote:
>> Hi Sebastian,
>>
>> On 01.06.2016 13:07, Sebastian Hellmann wrote:
>>> Hi Markus,
>>>
>>> On 01.06.2016 12:58, Markus Kroetzsch wrote:
>>>> On 01.06.2016 10:46, Sebastian Hellmann wrote:
>>>>> https://en.wikipedia.org/wiki/Unique_name_assumption
>>>>
>>>> The UNA is a principle in formal logic and knowledge
representation.
>>>> It is not really related to this discussion. For example,
standard
>>>> DBMS all make the UNA, but you can still have many
identifiers (keys)
>>>> for the same object in a database.
>>>
>>> Then the database does not use UNA. The above sentence reads
like you
>>> could have two primary keys, but then still have them pointing
to the
>>> same row.
>>> UNA means, if you have two identifiers A, B you add a triple A
>>> owl:differentFrom B at all times.
>>
>> I don't think that this mixing of different notions is making
much sense.
>
> Makes totally sense to me, since they are all quite similar. Entity
> Relationship Diagram are similar to Onologies/RDF, SPARQL is often
> implemented using Relational Databases.
> The relational model
https://en.wikipedia.org/wiki/Relational_model by
> Codd is consistent with first-order predicate logic as are many
> description logics, in particular a less expressive fragment was
used to
> design OWL
https://en.wikipedia.org/wiki/Description_logic#First_order_logic
Sorry, but you are mixing up things again here. Being "similar" is not
enough to establish a logical relationship between two formalisms. Eve
the underlying logic (FOL here) is just one aspect. OWL semantics is
based on *entailment* of logical consequences in FOL. In contrast,
Relational Algebra is based on *model checking* with respect to finite
FOL models. The two tasks are totally and fundamentally different
(model
checking is PSpace complete, entailment checking is undecidable, for a
start). It's beyond this thread to explain all details relevant here,
and the somewhat vague notion of "UNA" does not really do it justice
either (UNA is really a property of a logic's model theory, but
does not
tell you whether you are doing model checking or entailment).
>
>> Every SPARQL processor under simple semantics makes the UNA
>
> What is simple SEMANTiCS?
"Simple semantics" is the most basic way of interpreting RDF
graphs. If
you would like to know more, then you could start with the spec:
https://www.w3.org/TR/rdf11-mt/#simple-interpretations
Most SPARQL processors do not go beyond this, though their
semantics is
specified differently (based on model checking rather than on
entailment, which makes it more natural to talk about, e.g., negation
and aggregates). Nevertheless, the simple semantics is kind of built
into the SPARQL BGP semantics already, so you cannot do anything
less if
you implement SPARQL.
> Primary key in SPARQL stores backed with
> relational db's often have the Quad {?g {?s ?p ?o}}as the
primary key.
> De facto, UNA produces contradictions as soon as you want to
state that
> to things are the same. So owl:sameAs would not make sense
combined with
> UNA as it would always cause contradictions, except in the
reflexive case.
> Just because you are not unifying merging identifiers right away
does
> not imply UNA.
I cannot make sense of these sentences. UNA is a property of the
semantics you use, which in turn is determined by the tool (reasoner)
you apply. You cannot "imply UNA" -- either you implement it or you
implement something else. How you implement equality reasoning (by
"merging identifiers", for example) is entirely unrelated. You can
perfectly well capture equality reasoning in a UNA system using
auxiliary axioms. None of this has anything to do with how you
identify
quads in SPARQL.
>
>> , while RDF and OWL entailment regimes for SPARQL do not make
it. This
>> has nothing to do with how you model concepts and their IDs in your
>> domain. You can have the same data and use it in different SPARQL
>> tools, sometimes with a UNA sometimes without,
> there are SPARQL tools that throw a contradiction, if they encounter
> owl:sameAs
>
>> but your choice of modelling identifiers is not affected by that.
>
> OWL was designed to handle multiple identifiers. This affects the
> modeling in a way that it is fine to have several IDs.
> DBpedia as such uses this. Below are all ID's for DBpedia
Berlin., where
> the first one is the canonical one. A good idea might be to provide
> <http://dbpedia.org/pagid/3354> as well in the future. We are
working on
> a service that allows to canonicalize all DBpedia Ids, which is only
> legit as there is no UNA intended in OWL.
Thanks for reminding us of the various URIs you have in DBpedia
(keeping
some connection to the topic of this thread ;-). The relationship with
UNA is again not so relevant here. It is not true to say that you can
only have several identifiers because OWL does not have a UNA.
Instead,
it is correct to say that asserting several identifiers to be
semantically equal (in the sense of sameAs) is only useful if you have
no UNA. But this statement is really trivial: a logic with UNA
never has
a built-in equality (this would be a design error). However, a
logic may
use UNA and axiomatize an equality predicate to achieve the same
results
in query answering. In some logics, you cannot even detect at all
whether the UNA has been made or not when using positive queries
(OWL QL
is a typical example).
My main point is that none of these intricate discussions of ontology
semantics based on mathematical logic have anything to do with the
choice of a user to have more than one identifier for a concept. You
will encode the fact that something is an identifier in different ways
depending on what ontology language you use, but the discussion is
really on another level. Many data collections we are talking
about have
no logical semantics at all, yet they may use multiple identifiers for
one thing. I am sure that Tom's example of multiple identifiers in
Freebase is a purely technical approach based on redirects and API
"synonyms" without any commitment to a specific logic.
Cheers,
Markus
--
Markus Kroetzsch
Faculty of Computer Science
Technische Universität Dresden
+49 351 463 38486 <tel:%2B49%20351%20463%2038486>
http://korrekt.org/
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Sebastian Hellmann
AKSW/KILT research group at Leipzig University
Insitute for Applied Informatics (InfAI) at Leipzig University
DBpedia Association
Events:
* *April 24, 2016* Submission Deadline, SEMANTiCS 2016: Workshop &
Tutorial Proposals
<https://docs.google.com/document/d/1VOWyU9Oo2KOuRh09R9CJeC9aWcSNokDW4yHeuGHICPI/pub>
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* *Sep 12th-15th, 2016* SEMANTiCS 2016, Leipzig <http://semantics.cc/>
Venha para a Alemanha como PhD: http://bis.informatik.uni-leipzig.de/csf
Projects: http://dbpedia.org, http://nlp2rdf.org,
http://linguistics.okfn.org, https://www.w3.org/community/ld4lt
<http://www.w3.org/community/ld4lt>
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