F2F1 Minutes Session 7
This is part of F2F1 Minutes.
OWL Working Group Meeting Minutes, 07 December 2007
DRAFT. Currently Under Review
- 1 RIF and OWL WG Collaboration
- 2 Fragments - OWL Prime
- 2.1 Slide: Agenda
- 2.2 Slide: Oracle 10gR2 RDF
- 2.3 Slide: 11gR1
- 2.4 Slide
- 2.5 Slide: "Why?"
- 2.6 Slide 7: OWL subsets supported
- 2.7 Slide: semantics characterized by entailment rules
- 2.8 Slide: Applications of partial dl semantics
- 2.9 Slide: support semantics beyond owl prime
- 2.10 Slide 13: Advanced options
- 2.11 Slide: implementation in rules
- 2.12 Post Presentation Q & A
- 2.13 IRC aside on specifications, definitions, and implementations
- 3 Fragments: (Tractable) Fragments and other Fragment Proposals
- 4 Semantic Subsets
See also: IRC log
- Michael Smith
RIF and OWL WG Collaboration
Alan Ruttenberg: there is a proposal to have a joint OWL & RIF task force
Alan Ruttenberg: ... peter is there. is there anyone else?
Alan Ruttenberg: ...uli is a second.
Sandro Hawke: I may sort of be on it for both
Bijan Parsia: I am liason to RIF and will continue to be
Fragments - OWL Prime
Slides for this session: Media:zhe-f2f1.pdf
Slide: Oracle 10gR2 RDF
Some technical difficulties continued w.r.t slide presentation
Zhe Wu: many ways to insert data.
Zhe Wu: ...in 10r2 we also support some inferencing and rules. we use forward chaining approach
Zhe Wu: ...also query using a SPARQL-like syntax
Zhe Wu: ... this was all in 2005
Zhe Wu: this year new release with new features. faster loading, owl reasoning with proof generation
Zhe Wu: ... overhauled performance w.r.t. load and query
Zhe Wu: ... just recently added Jena / Oracle adapter
Zhe Wu: ... joint with HP
Zhe Wu: subset of owl is supported
Uli Sattler: i'm curious about what scalable and efficient means
Zhe Wu: i will show some numbers later
Zhe Wu: ... re: what is supported - forward chaining rules implementation for fast query answer
Zhe Wu: ... conclusion in ISWC 2006 paper was that existing reasoners had problems with large ABox data
Slide 7: OWL subsets supported
Zhe Wu: rdfs++ added as a "minimal" extension to RDFS
Zhe Wu: ...owl prime, what is now proposed as rdfs 3.0
Slide: semantics characterized by entailment rules
Zhe Wu: owl prime has ~50 rules
Slide: Applications of partial dl semantics
Slide: support semantics beyond owl prime
Jeremy Carroll: question about example being supported directly in the future
Zhe Wu: exactly
Achille Fokoue: question about updates to abox
Zhe Wu: i'll get to that later
Slide 13: Advanced options
Alan Ruttenberg: question about time, can we focus on questions now
Zhe Wu: ok, i'll quickly browse remaining slides, then go to questions
Slide: implementation in rules
Zhe Wu: I want to stress that we did not handle one property at a time
Zhe Wu: I'll jump to query answering slide
Zhe Wu: ...that's all I wanted to cover, open for questions
Post Presentation Q & A
Ian Horrocks: the tractable fragments doc describes fragments with known database mapping. wondering why you didn't choose one of those
Zhe Wu: we started by asking existing customers what they needed. most told us they just needed simple extension into owl from rdf
Zhe Wu: ... pretty much the approach was driven by customers and need to implement efficiently
Ian Horrocks: but, customers said you needed something small (rdf + a bit) which is exactly what the fragments are. instead you chose a large fragment and implemented incompletely
Zhe Wu: so far, for those other fragments we have not found a complete rule set (except PD*)
Uli Sattler: I want to echo ian and point out that you don't allow intersection, but a clever user would have it
Uli Sattler: ...and to be complete complexity becomes a problem
Alan Ruttenberg: they're not trying to be complete
Boris Motik: echo ian, observes that fragments exist which can be implemented with a set of complete rules
Bernardo Cuenca Grau: i'm worried about soundness and worried about what "sound and complete" means here. I don't understand the semantics
Bernardo Cuenca Grau: ...b/c you haven't implemented the OWL semantics, you've chosen some of the OWL DL vocabulary
Zhe Wu: we do care about completeness, but don't consider it critical
Zhe Wu: ... completeness is evaluated w.r.t. query answering for some benchmarks, etc.
Jeremy Carroll: what I hear from customers echos Zhe's comments.
Jeremy Carroll: ...I note that much of the questioning is hostile
Alan Ruttenberg: I agree
Jeremy Carroll: that may be b/c much of the questioning is coming from members with different user groups
Ian Horrocks: it wasn't intended to be hostile. I was trying to understand whether Oracle would be interested in more well understood and explainable fragments
Ian Horrocks: ...e.g., dl-lite which can be implemented in a database system, and also in a rule system
Discussion of PD* soundness and completeness in a rule based implementation, which scribe didn't capture
Ian Horrocks: the problem with PD* is that it doesn't implement a subset of OWL, it implements PD*
Jeremy Carroll: it depends on what you mean by fragment of OWL
Alan Ruttenberg: I hear interest in co-ordinating on database fragments with Oracle
Bijan Parsia: to standardize a fragment, we need a well defined specification that we can all understand
IRC aside on specifications, definitions, and implementations
The following IRC conversation happened in parallel to the in room verbal conversation and some other IRC exchanges. It continued until Ivan the point in the minutes where Ivan requests an end to side conversations (just before Semantic Subsets)
Fragments: (Tractable) Fragments and other Fragment Proposals
Bernardo Cuenca Grau: motivation of owl-lite was easier owl. b/c owl dl and full are rich and complex.
Bernardo Cuenca Grau: ...problem is owl-lite is broken b/c it doesn't address interactions between constructors
Bernardo Cuenca Grau: most features held out of owl-lite can be recovered through "back doors"
Bernardo Cuenca Grau: existing document includes fragments which
Bernardo Cuenca Grau: .... are well understood, documented, etc.
Bernardo Cuenca Grau: we don't expect users to go over recent literature on tractable fragments, so wanted a single document
Bernardo Cuenca Grau: most of the languages I will describe are "families" of languages, we decided to keep 1 from each
Bernardo Cuenca Grau: 1st is EL family
Bernardo Cuenca Grau: ...used in bio-medical already
Bernardo Cuenca Grau: stress that these fragments are not academic exercises, there are direct applications to existing ontologies
Bernardo Cuenca Grau: 2nd is DL-Lite family
Bernardo Cuenca Grau: ... designed for large number of instances in database technology
Bernardo Cuenca Grau: approach is similar to what zhe described, do work in tbox, then pass to database system for query answering
Carsten Lutz: reiterate bernardo, but contrast with zhe's approach. dl-lite change the ontology to use database technology, not change the database technology
Alan Ruttenberg: another difference is in oracle you can query for classes, in dl-lite only instances
Bernardo Cuenca Grau: you can do tbox reasoning, but designed for abox answering.
Bernardo Cuenca Grau: I picked the particular dl-lite language b/c it is between rdfs schema and owl dl
Bernardo Cuenca Grau: next is Horn-SHIQ
Bernardo Cuenca Grau: ...can reason without disjunctions
Bernardo Cuenca Grau: ...and low complexity for query answering
Bernardo Cuenca Grau: other fragments dlp as a bridge to rules
Bernardo Cuenca Grau: ... but it may be more "hacky" that horn-shiq
Bernardo Cuenca Grau: questions for wg
Bernardo Cuenca Grau: ....1 do we fix owl lite
Bernardo Cuenca Grau: ....2 does that mean select one of these fragments
Bernardo Cuenca Grau: ....3 or do we present a menu of fragments?
Bernardo Cuenca Grau: not in slides - do we want semantic subsets of owl full?
Bernardo Cuenca Grau: ....e.g., owl full versions of these fragments? do we care about complexity of the full fragments? about compatibility?
Ivan Herman: request to drop side conversations
Ivan Herman: ... and focus
Alan Ruttenberg: little time, can we start with semantic subset of owl full?
Ian Horrocks: semantic subset means no change to syntax, but sanction smaller set of conclusions
Jeremy Carroll: example is pd*, which specifies what semantic rules are thrown away
Peter Patel-Schneider: pd* throws away *parts* of rules
Ian Horrocks: this is picky
Alan Ruttenberg: how comfortable are people with this type of fragment
Alan Ruttenberg: ... does anyone want to say this is a lousy idea.
Peter Patel-Schneider: yes, its lousy b/c you can be arbitrarily picky
Ian Horrocks: its a lousy idea b/c it blows away the idea of interoperability
Bijan Parsia: qualm that methodological design principles are "unclear"
Bijan Parsia: ...guidance for making decisions seem more arbitrary, a dangerous rat-hole
Bijan Parsia: ... would rather people say they are incomplete than building incompleteness into fragments
Jeremy Carroll: in response to ian, any semantic subsetting would need to be clear that it is a subset of spec and an explicit, agreed semantic subset
Jeremy Carroll: ...e.g., oracle and hp would agree on semantic subset and interop on at-least the semantic subset
Alan Ruttenberg: if we call this fragment or conformance level, it seems useful
Alan Ruttenberg: ...that baseline entailments are necessary, but additional entailments may be ok
Bijan Parsia: if we shift from language fragments to reasoner conformance I'm more comfortable
Sandro Hawke: Bijan, "Reasoner Conformance" might be a more useful notion here than "Language Fragments".
Sandro Hawke: ...I have examples of people specifying this at a tool level.
Jeremy Carroll: i'd be happy with such a rewording. i don't see it as notable
Alan Ruttenberg: does such a distinction help others
some affirmation to alan in room
Zhe Wu: ?
Alan Ruttenberg: he said it would be useful to say we support same entailments
Ian Horrocks: more comfortable defining conformance that fragments
Bernardo Cuenca Grau: users are comfortable with incomplete reasoning. swoop offering rdfs reasoner as a choice is an example of this
Bernardo Cuenca Grau: ...more comfortable with that than trying to specify semantic subsets
Jeff Pan: i agree with bernardo and others.
Jeff Pan: ... implementation does not specify fragment.
Boris Motik: i just looked at pd* , this seems like definition. I think it is a useful fragment if evaluated a certain way.
Ian Horrocks: i didn't say pd* was bad, that we'd be standardizing an implementation. it was a reaction to jeremey's comments on what hp and oracle might do
Sandro Hawke: owl is unique to me b/c it doesn't specify what the tools do, people read into that. specifying the tools would be useful. as a customer I expect that and would like it
Bijan Parsia: justifying discomfort - seems likely that over time fragments specified in such a way are likely to move
Bernardo Cuenca Grau: on sandro's comment - we should specify reasoning services
Bernardo Cuenca Grau: ... it's not in the spec for OWL DL. for fragments the services descriptions would be useful
Sandro Hawke: i don't know what the terms are, the market decides
Ian Horrocks: its difficult to imagine semantic subsets not drifting apart
Ian Horrocks: ... it has been a success for owl that interoperability is so good, considering
Jeremy Carroll: responding to standardizing tools - yes. there is value to user if they know different tools perform the same
Jeremy Carroll: ... this wg could provide appropriate conformance levels where vendors and user community come together
Jeremy Carroll: ... clear that motivations from academic community are useful, but they aren't the only motivations
Alan Ruttenberg: no one is saying market is unimportant
Uli Sattler: clarification on user needs?
Jeremy Carroll: users need some sort of specification, but don't need to know behavior is exact
Alan Ruttenberg: I want to poll for consensus on how to procede
Sandro Hawke: i don't understand
Alan Ruttenberg: I want to know if people think these fragments are useful
Alan Ruttenberg: ... defined as a minimum set of entailments
Bijan Parsia: reasoners can conform to the language to different degrees
Alan Ruttenberg: we should aim for something specified like pd*
Ian Horrocks: declarative...
Alan Ruttenberg: yes, declarative
Uli Sattler: we would later know e.g., what it would mean for a reasoner to conform to particular level?
Alan Ruttenberg: yes.
Jeff Pan: what does conformance level mean? is it in terms of benchmark?
Uli Sattler: provides example
Carsten Lutz: degrees of incompleteness?
Alan Ruttenberg: degree of completeness
Alan Ruttenberg: ...fragments are syntactic fragments
Alan Ruttenberg: ...conformance levels are distinct
Jeff Pan: there might be difference between alan's and uli's suggestions
Alan Ruttenberg: distinction is unimportant now
Alan Ruttenberg: reads Q1 as above