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Re: status of xsd:duration in OWL (and RIF and SPARQL) - ACTION-164: RDF WG

From: Ivan Herman <ivan@w3.org>
Date: Thu, 2 Aug 2012 11:01:07 +0200
Cc: Martin Hepp <martin.hepp@ebusiness-unibw.org>, 'Dan Brickley' <danbri@danbri.org>, "public-vocabs@w3.org" <public-vocabs@w3.org>
Message-Id: <3A999D21-A61A-4682-9F21-47C0EC067330@w3.org>
To: "Evain, Jean-Pierre" <evain@ebu.ch>

On Aug 2, 2012, at 10:35 , Evain, Jean-Pierre wrote:

> Hi Ivan,
> 
> Good to know and long expected. How does this now relate to the discussion around OWL. Will RDF adoption of these datatypes leads to OWL adopting it too?

I cannot say at this moment...

Ivan



> 
> Best regards,
> 
> Jean-Pierre
> 
> -----Original Message-----
> From: Ivan Herman [mailto:ivan@w3.org] 
> Sent: jeudi, 2. août 2012 10:27
> To: Martin Hepp
> Cc: Evain, Jean-Pierre; 'Dan Brickley'; public-vocabs@w3.org
> Subject: Re: status of xsd:duration in OWL (and RIF and SPARQL) - ACTION-164: RDF WG
> 
> FWIW, both xsd:time and xsd:date are perfectly fine datatypes in RDF now:
> 
> http://www.w3.org/TR/2012/WD-rdf11-concepts-20120605/#xsd-datatypes
> 
> Ivan
> 
> 
> On Aug 2, 2012, at 10:19 , Martin Hepp wrote:
> 
>> As a side note, the flow of argument in the forwarded reply shows that the core Semantic Web community is designing formal languages but not formal languages for Web ontologies.
>> 
>> The limitations of reasoning with xsd:time and xsd:data are microscopic in comparison to the challenges of any reasoning over data published at Web scale - by millions of site owners, from millions of existing databases etc. 
>> 
>> Best
>> 
>> M. Hepp
>> 
>> 
>> On Aug 1, 2012, at 7:45 PM, Evain, Jean-Pierre wrote:
>> 
>>> Hi Dan,
>>> 
>>> Here is one part of the discussion as a response to my request to consider date and time separately in addition to duration...
>>> 
>>> There is more... still digging
>>> 
>>> JP
>>> 
>>> -----Original Message-----
>>> From: Evain, Jean-Pierre 
>>> Sent: mardi, 8. mai 2012 11:18
>>> To: 'Michael Schneider'
>>> Cc: 'Ivan Herman'; Bijan Parsia; Ian Horrocks; public-owl-wg@w3.org; Public-Rif-Wg (E-mail); Peter F. Patel-Schneider; Sandro Hawke
>>> Subject: RE: status of xsd:duration in OWL (and RIF and SPARQL) - ACTION-164: RDF WG
>>> 
>>> Dear Michael,
>>> 
>>> I appreciate your time and effort in trying to bring more background around the current situation.
>>> 
>>> I must say that I am growingly puzzled. This is definitely making me question my resolution to move for these technologies. If it cannot provide simple answers to simple questions, then maybe I am wasting my time. If I show your answer to some of my colleagues in my expert community, I may get some buying from those who have an academic background, but not from implementers (who are those who count to me in my daily business).
>>> 
>>> I believe that the semantics of time, date and duration are clear and I am surprised that they may be considered as being not mathematically univocally representable. For me there is nothing more semantically defined than a datatype bound to a particular format (and you'll always find cases where representation of date and time is ambiguous whether you use date, time or dateTime). A class instantiating such a datatype is also semantically defined in the context of a given ontology. Etc.
>>> 
>>> I believe working on the duration example would seem to answer part of the question but it is taking the easy way and in this particular case:
>>> - you have taken an arbitrary time reference that is a second (what about tenth or thousandth of a second)
>>> - you are facing the problem of defining the type of month according to its duration and resolving this as suggested looks interesting :--(
>>> - then once you have calculated the value, how do you say on which basis it was calculated (e.g. how do you signal the unit unless it has to be seconds:--(, etc.)?
>>> 
>>> Why not simply reuse the xsd datatypes? That would solve all the above problems with a simple expression in a well defined format. What do I miss?
>>> 
>>> But you didn't really answer my question about expressing a start time in a video.  This is semantically perfectly clear and defined. I'd like to see an example of how this would be done and could be recognised as good practice by implementers.
>>> 
>>> I am not saying that you are wrong. You seem to have been thinking about it.. But I believe we do not live in the same world.:--) I am personally trying to be very practical and I realise that this technology may never fulfil my requirements to serve uniquely some theoretical purpose on improbable queries.
>>> 
>>> I am really wondering if this makes sense. Please convince me.
>>> 
>>> Jean-Pierre
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> -----Original Message-----
>>> From: Michael Schneider [mailto:schneid@fzi.de] 
>>> Sent: mardi, 8. mai 2012 10:39
>>> To: Evain, Jean-Pierre
>>> Cc: 'Ivan Herman'; Bijan Parsia; Ian Horrocks; public-owl-wg@w3.org; Public-Rif-Wg (E-mail); Peter F. Patel-Schneider; Sandro Hawke
>>> Subject: Re: status of xsd:duration in OWL (and RIF and SPARQL) - ACTION-164: RDF WG
>>> 
>>> Hi Jean-Pierre!
>>> 
>>> Am 08.05.2012 09:25, schrieb Evain, Jean-Pierre:
>>> 
>>>> I understand the point which is being made being what is useful for reasoning or not.
>>> 
>>> Replace "useful for reasoning" by "required for the well-definedness of 
>>> the semantics" of OWL 2 or RIF!
>>> 
>>> It is a basic technical requirement for the specifications of these 
>>> languages that for every syntactically well-formed expression (aka an 
>>> OWL 2 ontology or a RIF rule set), the semantic meaning can be 
>>> determined by mathematical means. At a minimum, for OWL 2 and RIF, this 
>>> means that it can always be determined whether an input ontology is 
>>> satisfiable or not, or whether one given ontology entails another given 
>>> one or not. Only in the cases of OWL 2 DL and its profiles, it is an 
>>> additional requirement (by design) that there are reasoning procedures 
>>> that are able to do these determinations in an automated way for all 
>>> input, because these languages are required to be computationally 
>>> decidable. But having a well-defined semantics is always needed. 
>>> Clearly, if there are ontologies for which it cannot uniquely be deduced 
>>> (mathematically) whether they are satisfiable or not, a reasoner cannot 
>>> give the "right" reasoning result for them, because it cannot then be 
>>> determined whether it's answer is right or not, or just one correct 
>>> answer out of many.
>>> 
>>> To illustrate this problem, take the case of xsd:duration in its 
>>> definition as of the time of finalizing OWL 2, where each literal of 
>>> xsd:duration would essentially denote a pair (m, s) consisting of a 
>>> certain number m of month plus a certain number s of seconds. Let there 
>>> be two such durations:
>>> 
>>>   d1 := (2, 0)
>>>   d2 := (1, 30*24*60*60)
>>> 
>>> Now, depending on what is meant by "a month", these two durations can 
>>> represent either (i) the same value (if a month has 30 days), or (2) d1 
>>> can be greater than d2 (if a month has 31 days), or (3) d1 is smaller 
>>> than d2 (if a month has, say, 28 days = 4 weeks). I may well have missed 
>>> a precise definition of "a month" in the (newest version of the) XSD 
>>> spec, in which case the above example may be void. But if not, then it 
>>> is clear that any OWL 2 (+xsd:duration) ontology for which the question 
>>> of satisfiability depends on whether the above two durations are the 
>>> same or not, or which of them is greater, does not have a uniquely 
>>> defined semantic meaning.
>>> 
>>> An example for the need of being able to determine whether equality 
>>> between two duration values holds or not would be an ontology with data 
>>> enumerations consisting of duration values (denoted by "d1" and "d2", as 
>>> defined above, but in a real ontology one would use their correct 
>>> literal form, of course):
>>> 
>>>   :D a rdfs:Datatype ;
>>>      owl:oneOf ( d1 ) .
>>>   :dp a owl:DatatypeProperty ;
>>>       rdfs:range :D .
>>>   :s :dp d2 .
>>> 
>>> This set of axioms should be satisfiable if and only if d2 = d1, because 
>>> only in this case, the object d2 of the property assertion (last 
>>> statement) would denote an instance of the singleton datatype :D = {d1}. 
>>> But if it cannot be determined whether d2 equals d1 or not, then it 
>>> cannot be determined whether the axiom set is satisfiable or not.
>>> 
>>> An example for the need of comparison of two durations (greater or 
>>> lesser than) could be constructed from the use of OWL 2 datatype 
>>> restrictions.
>>> 
>>>> But does that mean that all other information is garbage?
>>> 
>>> Everyone can say everything about everything. But an OWL 2 or RIF or 
>>> whatever language specification with a formal semantics at its core 
>>> would, if not well-defined, IMO count as just that: garbage. :-)
>>> 
>>> Best,
>>> Michael
>>> 
>>> -- 
>>> ..........................................................
>>> Dipl.-Inform. Michael Schneider
>>> Research Scientist, IPE / WIM
>>> 
>>> FZI Forschungszentrum Informatik
>>> Haid-und-Neu-Str. 10-14
>>> 76131 Karlsruhe, Germany
>>> Tel.: +49 721 9654-726
>>> Fax: +49 721 9654-727
>>> 
>>> michael.schneider@fzi.de
>>> www.fzi.de
>>> 
>>> ..........................................................
>>> Forschungszentrum Informatik (FZI) an der Universität Karlsruhe
>>> Stiftung des bürgerlichen Rechts
>>> Stiftung Az: 14-0563.1 Regierungspräsidium Karlsruhe
>>> Vorstand: Dipl. Wi.-Ing. Michael Flor, Prof. Dr. Ralf Reussner,
>>> Prof. Dr. Rudi Studer, Prof. Dr.-Ing. J. Marius Zöllner
>>> Vorsitzender des Kuratoriums: Ministerialdirigent Günther Leßnerkraus
>>> ..........................................................
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>> 
>> --------------------------------------------------------
>> martin hepp
>> e-business & web science research group
>> universitaet der bundeswehr muenchen
>> 
>> e-mail:  hepp@ebusiness-unibw.org
>> phone:   +49-(0)89-6004-4217
>> fax:     +49-(0)89-6004-4620
>> www:     http://www.unibw.de/ebusiness/ (group)
>>        http://www.heppnetz.de/ (personal)
>> skype:   mfhepp 
>> twitter: mfhepp
>> 
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>> 
>> 
>> 
>> 
> 
> 
> ----
> Ivan Herman, W3C Semantic Web Activity Lead
> Home: http://www.w3.org/People/Ivan/
> mobile: +31-641044153
> FOAF: http://www.ivan-herman.net/foaf.rdf
> 
> 
> 
> 
> 
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----
Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
FOAF: http://www.ivan-herman.net/foaf.rdf
Received on Thursday, 2 August 2012 09:01:37 GMT

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