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>
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
> http://korrekt.org/
>
>
> ------------------------------------------------------------------------------
> What NetFlow Analyzer can do for you? Monitors network bandwidth and
> traffic
> patterns at an interface-level. Reveals which users, apps, and protocols
> are
> consuming the most bandwidth. Provides multi-vendor support for NetFlow,
> J-Flow, sFlow and other flows. Make informed decisions using capacity
> planning reports. https://ad.doubleclick.net/ddm/clk/305295220;132659582;e
> _______________________________________________
> DBpedia-discussion mailing list
> DBpedia-discussion@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/dbpedia-discussion
>
------------------------------------------------------------------------------
What NetFlow Analyzer can do for you? Monitors network bandwidth and traffic
patterns at an interface-level. Reveals which users, apps, and protocols are
consuming the most bandwidth. Provides multi-vendor support for NetFlow,
J-Flow, sFlow and other flows. Make informed decisions using capacity
planning reports. https://ad.doubleclick.net/ddm/clk/305295220;132659582;e
_______________________________________________
DBpedia-discussion mailing list
DBpedia-discussion@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/dbpedia-discussion
