See also: IRC log
<jjc> Semantics break out
<jjc> scribenick: jjc
Four issues at
Blank Nodes, SPARQL-Style RDF Semantics
Archaisms, Literals as Subjects
Jeremy and Peter do not like SPARQL-Style RDF Semantics
as a title
Evan: let's start with the easy bits
Paul: rdf:value - keep this to deal with literals as subjects
List of Archaisms under syntax:
* reification (align with some "named graph" support)
* rdf:Alt (just remove)
* rdf:Bag (fix or remove)
* rdf:Seq (use rdf:List instead; it's costly to have two similar options)
* xs:string (use plain literals instead)
* rdf:XMLLiteral (use plain literals instead, with quoted XML)
* rdf:ID (use rdf:about instead)
What should we do for these?
discussion of Archaisms
reification: Jeremy - there is no semantics
containers: Jeremy there is no semantics
Peter: yes there is container membership
Paul: what do we want to do
Peter: no one knows what containers mean
Paul: I am reluctant to deprecate something which we do not have equivalent
Peter: we do, you can roll your own
Jeremy: if we are going to depreacte anything, we deprecate Alt
James: let's add to the list for discussion
Peter: we could remove axiomatic triples for rdf:_nn
and hence all the semantics
Paul: are we happy with the semantics of xs:string and plain literals being different
Jeremy: they're not - most widely misimplemented part of RDF Semantics
Peter: simple and D entailments to do with these string literals are different
rathole into whether we can have inconsistency of RDF or is it RDFS
In RDFS you can get an inconsisteny with an ill-typed XML Literal
in D semantics also illformed xsd literals
<scribe> ACTION: pfps edit wiki to include list of Archaism [recorded in http://www.w3.org/2010/06/27-rdfn-s-minutes.html#action01]
Jeremy: does anyone else have other Archaims
e.g. ill-formed lists
Peter: this would be a big change to the semantics
you could infer sameAs
brief discussion of rdfs:comment etc.
James: does mulgara change the labels internally
Paul: no -we reserve the right to
Jeremy: I don't like the wording
James: is it about scope
Paul: qu about SPARQL and b node semantics
Ian apparently claims that current semantics of blank nodes creates NP complete problem in SPARQL
Jeremy: but subgraph isomporphism is there anyway because of variables
and this is NP complete
Paul: but we have b node semantics documented
but not used
Peter: maybe it was a mistake to talk about entailment
then we talk about query instead
But maybe this becomes a SPARQL issue
that they should not talk about entailment
Before break: Jeremy we are not progressing
Evan: but you seem to be making progress on entailment issue
<ekw> scribenick: ekw
paul: we should look at blank
nodes and decide if they are addressable
... put it forward as a proposal or say its not something we can do
alejandro: people are using blank nodes in different ways
<pfps> we need to remember to put in stuff to fix the inference rules
alejandro: why can DBpedia create a huge
DB without them, while others can't
jjc: people think that they
shouldn't use them, but then they misuse other features to do
the same thing
... I think that we have agreed that the formal semantics of RDF will change, but the informal semantics should preserve the blank node disctinction
alehandro: do we need a suggested way of handling this (the pragmatic support for blank nodes)
pfps: there are two things that
we could do
... we could decide that blank nodes as currently spec'd are just bad
... you might just decide "There are no blank nodes in RDF graphs."
jjc: a blank node is a node who's name that we don't know rather than a node without a name (an existential)
pfps: the semantics wouldn't have to change for this
jjc: we could delete the text describing blank nodes as an existential since people don't understand it anyway
paul: if we go to SemTech and talk with org's using this stuff, how are they looking at blank nodes?
jjc: the smallest change would be
to provide a skolemization algorithm for blank nodes
... however that wouldn't address the issue of the folks who are against using blanknodes
paul: this could change the ways
... I don't know if it breaks what's out there, but it certainly changes the story.
jjc: another con is it may make it harder to compare 2 graphs using graph isomorphism
paul: we have established that
blank nodes could benefit from some work
... is it possible with working on blank nodes that it could change the semantics? If so, we should record this.
jjc: should we look at literals as subjects now?
PFPS not JJC on last comment
paul: I can't think of a use case
for a literal as a predicate, but can for a literal as a
... 3 squareRootOf 9 for example
Stephan: What's the danger of this?
jjc: A con is that rdf/xml
changes would be significant.
... as pro it would actually simplify some situations.
... on OWL systems, its difficult but in a triple store system it's significantly easier.
Some discussion about how this relates to the restriction on InverseFuntional properties in OWL.
Going forward this would add more divergence between RDF and OWL (causing a document fork)
Stephan: I don't find these use
cases compelling enough to justify this change.
... what I have mind is the social impact that this would have.
This could cause people to make statements about the string instead of about the entity.
Paul: lack of this feature has
... such as in data bases of pseudo primes.
jjc: I don't think we should be
neutral about it. I think this group should say that this
feature is not worth doing.
... although one of the things that TBL wants is graph literals as subjects.
Paul: how about a best practice of making a blank node sameAs a literal, and use the blank node as a subject everywhere?
Stephan: That would be to me,
shooting yourself in the foot.
... I feel unhappy about these type of proposal.
... what's wrong with suggesting that a group investigate this and collect use cases?
subtopic: SPARQL-style semantics
jjc: I would suggest that introductory blurb should talk about RDF as a data language rather than "as seen in SPARQL systems"
[scribe had to leave the room for a half hour]
<AndyS> Issues of simplified RDF semantics
<AndyS1> Scribe: Andy Seaborne
<AndyS1> scribenick: AndyS
Section: Semantics for Next
... datasets: alternatives appraoches for semantis need to be
... considered including model theoretic or (if now normative) entailment rules
Are named graphs first class citizens? Both "yes" and "no" are possible.
JJC: Q: what is the relationship of two named graphs in a single document? If any (leave pragmatic)?
PFPS: When synatx is done, not all work is done.
-> require that any extensions come with semantics
Section: Blank Nodes
add possibility of global naming for blank nodes (not URIs , maybe URIs - alternatives)
Issue: currently reading twice creates different bnodes - preserve this?
JJC: (round tripping
... want to round trip i.e. preserver references, across serialization and exchange.
... e.g. "this bnodes (triples using...) have changed"
Blank nodes ... remote references use cases ...
scribe: skolemized: what is not yet skolemized?
skolemization is not bnode label
scribe: editting may not preserve
skolemization (large, ugly, not human friendly)
... speculation on possible solutions
... to scope space of possibilities
editting the blank nodes section
End of break out session
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