W3C home > Mailing lists > Public > semantic-web@w3.org > March 2011

Re: a blank node issue

From: Reto Bachmann-Gmuer <reto.bachmann@trialox.org>
Date: Sat, 5 Mar 2011 18:54:34 +0100
Message-ID: <AANLkTin4mJpv3tDE7a2BL8JHWWs+4Mw18kCStKF2huyO@mail.gmail.com>
To: Michael Schneider <schneid@fzi.de>
Cc: "semantic-web@w3.org" <semantic-web@w3.org>
I'd suggest adding a question regarding lean-graphs.

Given the following two graphs:

G1: {
  :alice ex:lixes <urn:isbn:1234>.
  <urn:isbn:1234> ex:author [ foaf:lastName "John"; foaf:firstName "Doe"].
}
G2: {
  :bob ex:lixes <urn:isbn:1234>.
  <urn:isbn:1234> ex:author [ foaf:lastName "John"; foaf:firstName "Doe"].
}

The merge without making it lean would be
M1: {
  :alice ex:lixes <urn:isbn:1234>.
  :bob ex:lixes <urn:isbn:1234>.
  <urn:isbn:1234> ex:author [ foaf:lastName "John"; foaf:firstName "Doe"].
  <urn:isbn:1234> ex:author [ foaf:lastName "John"; foaf:firstName "Doe"].
}

the lean version would be:
M2: {
  :alice ex:lixes <urn:isbn:1234>.
  :bob ex:lixes <urn:isbn:1234>.
  <urn:isbn:1234> ex:author [ foaf:lastName "John"; foaf:firstName "Doe"].
}

[ ] Pro lean: M1 and M2 express the same meaning, it's ok for an agent to
simplify M1 to M2.
[ ] Leanification has fallen into desuetude: M1 mean something different, M1
cannot be simplified to M2 without loosing information.
[ ] Can't say as it depends on the bnode-labels which are somehow hidden by
the turtle serialization above.
[ ] It depends on whether G1 and G2 are named graphs or not.
[ ] If M1 has a name it cannot be simplified, otherwise it can.

Cheers,
Reto


On Fri, Mar 4, 2011 at 2:51 PM, Michael Schneider <schneid@fzi.de> wrote:

> Hi all!
>
> Within the last few days my mailbox must have been hit by more mails about
> blank node issues as there are different blank node identifiers on the Web.
> It's these old discussions again and again: Should the syntactic scope of
> blank nodes be graph-local or global? Should the semantics of blank nodes be
> that of existentially quantified variables or skolem constants? Should there
> be blank node identifiers in the abstract RDF model or not? Some people seem
> to think that what was meant to be a syntactic property of blank nodes is
> actually a semantic one. Etc.
>
> As anyone else, I have strong opinions on all these questions, but it's
> Friday afternoon and I don't like to add just more comments here. Instead, I
> have created a small questionnaire based on some simple examples that take
> both syntactic and semantic aspects into account. It should be easy for
> anyone, depending on his or her preferences, to put the cross at the right
> place. Enjoy!  :-)
>
> Cheers,
> Michael
>
> ===== BEGIN BLANK NODE QUESTIONNAIRE ===
>
> Section 1: Syntactic Scope of Blank Nodes
> -----------------------------------------
>
> When merging the two below RDF graphs G1 and G2 into a single graph, what
> would be your /preferred/ result, regardless what the current RDF spec sais
> (all examples given in Turtle syntax)?
>
> G1: {
>     ex:FoafNamedPerson rdfs:subClassOf _:x .
>     _:x rdf:type owl:Restriction .
>     _:x owl:onProperty foaf:name .
>     _:x owl:allValuesFrom xsd:string .
> }
>
> G2: {
>     :alice foaf:knows _:x .
>     _:x rdf:type foaf:Person .
>     _:x foaf:name "Bob" .
> }
>
> [ ] Pro graph-local blank nodes:
>    The blank node identifiers should be /renamed/.
>     That is, after merging there will be /two/ distinct blank
>     node identifiers, one (e.g. "_:x1") substituting the "_:x" coming
>     from G1, and another one ("e.g. "_:x2") substituting the "_:x"
>    from G2.
>
> [ ] Pro global blank nodes:
>    The blank node identifiers should /not/ be renamed.
>    That is, the result graph will still contain
>     one single blank node identifier named "_:x".
>
> [ ] I don't know / I have no opinion
>
> Section 2: Semantics of Blank Nodes
> -----------------------------------
>
> Which of the following proposed "Simple" entailments should hold ("Yes") or
> not ("No") according to your opinion, regardless what the current RDF spec
> sais about Simple entailment in Sec. 2 of the RDF Semantics (format:
> "PREMISE-GRAPH |= CONCLUSION-GRAPH"; all examples given in Turtle syntax)?
>
> * Example 1 (graph serializations are exactly the same):
>
> {  :alice foaf:knows _:x . _:x foaf:name "Bob" . }
> |=
> {  :alice foaf:knows _:x . _:x foaf:name "Bob" . }
>
> [ ] Yes, this should be an entailment
> [ ] No, this should be a non-entailment
> [ ] I don't know / I have no opinion
>
> * Example 2 (graph serializations use different bnode identifiers):
>
> {  :alice foaf:knows _:x . _:x foaf:name "Bob" . }
> |=
> {  :alice foaf:knows _:y . _:y foaf:name "Bob" . }
>
> [ ] Yes, this should be an entailment
> [ ] No, this should be a non-entailment
> [ ] I don't know / I have no opinion
>
> * Example 3 (graph serializations use "anonymous bnodes"):
>
> {  :alice foaf:knows [ foaf:name "Bob" ] . }
> |=
> {  :alice foaf:knows [ foaf:name "Bob" ] . }
>
> [ ] Yes, this should be an entailment
> [ ] No, this should be a non-entailment
> [ ] I don't know / I have no opinion
>
> ===== END BLANK NODE QUESTIONNAIRE ===
>
> --
> Dipl.-Inform. Michael Schneider
> Research Scientist, Information Process Engineering (IPE)
> Tel  : +49-721-9654-726
> Fax  : +49-721-9654-727
> Email: michael.schneider@fzi.de
> WWW  : http://www.fzi.de/michael.schneider
>
> ==============================================================================
> FZI Forschungszentrum Informatik an der Universität Karlsruhe
> Haid-und-Neu-Str. 10-14, D-76131 Karlsruhe
> Tel.: +49-721-9654-0, Fax: +49-721-9654-959
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> Studer
> Vorsitzender des Kuratoriums: Ministerialdirigent Günther Leßnerkraus
>
> ==============================================================================
>
>
Received on Saturday, 5 March 2011 17:55:08 UTC

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