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Re: New proposal (Re: getting rid of xsd:dateTime ?)

From: Pierre-Antoine Champin <pierre-antoine.champin@liris.cnrs.fr>
Date: Wed, 06 Apr 2011 11:09:31 +0200
Message-ID: <4D9C2DCB.1060705@liris.cnrs.fr>
To: "Evain, Jean-Pierre" <evain@ebu.ch>
CC: 'Felix Sasaki' <felix.sasaki@fh-potsdam.de>, "public-media-annotation@w3.org" <public-media-annotation@w3.org>
On 04/06/2011 10:06 AM, Evain, Jean-Pierre wrote:
> Pierre Antoine,
> 
>  
> 
> I understand your last proposal but this will need to be very well
> documented

of course; see my answer to Felix

> otherwise:
> 
> - What will be found in instances may prove hazardous.

I may be biased, but I think most people crowling ma: data will query
them without relying on inference engines... If they do, they may use
Pellet or another engine that have no problem with those datatypes.
Finally, even a rule-based OWL-RL compliant inference engine can go
beyond the requirements and support additional datatypes.

So my guess is that "permissive" data will break only in very limited
cases...

> - It definitely makes the adoption of the ontology more
> difficult as the issues and implications of the options may be hard to grasp

I propose to add the following comment introducing the ontology:

  The ma: RDF ontology is compliant with the RL profile of OWL2 [ref].
  However, for data to be compliant with that profile, it should
  restrict the set of datatypes used for 'ma:date' and its subproperties
  to 'xsd:dateTime' a,d 'xsd:dtaeTimeStamp'.

It says 'compliant' so it should appeal to the concerned people. It
gives a simple recipe, so it should be easy enough to apply even if you
don't grasp all the implications.

> My take on your summary of the problem is that if people want to take
> maximum benefit from compliance they’ll have to use the dateTime format
> anyway.

yes; but again, my gut feeling is that the benefit will be marginal in
practice.

> It seems a bit tricky /misleading to offer the option of not
> being fully compliant (and again I agree that dateTime is not particular
> nice).

we are talking about being compliant *with OWL2-RL*, which is an
interesting feature, but not a requirement of all the linked data
community, nor from our charter. So I think it is ok.

  pa


> 
>  
> 
> Regards,
> 
>  
> 
> Jean-Pierre
> 
>  
> 
> *From:*public-media-annotation-request@w3.org
> [mailto:public-media-annotation-request@w3.org] *On Behalf Of *Felix Sasaki
> *Sent:* mercredi, 6. avril 2011 09:35
> *To:* Pierre-Antoine Champin
> *Cc:* public-media-annotation@w3.org
> *Subject:* Re: New proposal (Re: getting rid of xsd:dateTime ?)
> 
>  
> 
> Hi Pierre-Antoine,
> 
> 2011/4/6 Pierre-Antoine Champin <pierre-antoine.champin@liris.cnrs.fr
> <mailto:pierre-antoine.champin@liris.cnrs.fr>>
> 
> Felix,
> 
> On 04/06/2011 12:32 AM, Felix Sasaki wrote:
>> 2011/4/5 Pierre-Antoine Champin <pierre-antoine.champin@liris.cnrs.fr
> <mailto:pierre-antoine.champin@liris.cnrs.fr>
>> <mailto:pierre-antoine.champin@liris.cnrs.fr
> <mailto:pierre-antoine.champin@liris.cnrs.fr>>>
>>
>>     Hi all,
>>
>>     there seem to be a recurring problem with dates and the ma:
> ontology. I
>>     encountered it, Martin encountered it, I know that Joakim also did...
>>
>>     The fact is that most metadata formats we are dealing with allow dates
>>     to be more or less precise, like
>>
>>     * just a year
>>
>> in XML Schema, this would be gYear http://www.w3.org/TR/xmlschema-2/#gYear
>>
>>     * a year and a month
>>
>> this would be http://www.w3.org/TR/xmlschema-2/#gYearMonth
>>
>>     * a year, a month and a day
>>
>> this would be date http://www.w3.org/TR/xmlschema-2/#date
> 
> 
> You are completely right.
> 
> 
>>     * ...
>>
>>     while xsd:dateTime imposes to us to commit to a 1sec precision...
>>
>>     I suggest we change the range of date properties to rdfs:Literal, and
>>     specify in the documentation that they should be of the form
>>     YYYY[-MM[-DD[Thh[:mm[:ss[.fff]]]]]], to be interpreted as an
> incomplete
>>     date.
>>
>> This would be very bad. RDF in many areas is linked to XML datatypes,
>> see e.g. http://www.w3.org/TR/rdf-primer/#typedliterals , and I would
>> encourage us to follow this approach as close as possible. To solve your
>> problems, I would rather say that a date should be one of the above
>> built in XML Schema data types.
> 
> I probably jumped to fast to the proposal above, for the reasons
> explained below. Nevertheless I agree with you that a better solution
> would be that section 4.5 be rewritten:
> 
>  A Date value MUST be represented using one of the following XML
>  Schema datatypes: gYear, gYearMonth, date, dateTime, dateTimeStamp,
>  depending on the precision available on the data.
> 
> NB: I add dateTimeStamp which is new in XSD 1.1 [1], and imposes a
> timezone. I know that XSD 1.1. is not recommended yet, but OWL2 found a
> nice way to get around this problem [2].
> 
> This would have to be reflected in the API document as well [3].
> 
> 
> Now, if I had to do only pure RDF, I would be happy with this solution.
> My problem is that we have been asked in some comments to make the
> ontology compliant with the OWL2-RL profile which, I think, makes sense
> (OWL-RL inferences can be efficiently implemented on top of a rule
> language). And OWL2-RL does not support xsd:gYear or xsd:gYearMonth. In
> fact, on only support dateTime and dateTimeStamp [4].
> 
> Hence my first proposal to use the smallest common denominator
> (rdfs:Literal), although we lose some semantics in the process.
> 
> 
> Here is a second proposal that I think will suit you better: we leave
> the range of 'date' (and its subproperties) *unspecified* in the OWL
> ontology, and refer to the document to explain that only date-related
> datatypes are expected (and only dateTime[Stamp] are supported by OWL2-RL).
> 
> 
> 
> This sounds good to me, so also a +1 like Florian in this thread. I
> think it might be worthwhile to explain the issue in our spec, basically
> use your text in this thread, so that users understand the rationale.
> 
> Out of curiosity: Do you know why OWL2-RL only supports the above date /
> time related types?
> 
> Felix
>  
> 
> 
>     On the one hand, I'm afraid that this is only translating the problem
>     from the ontology to the data: if people publish data using a datatype
>     not supported by OWL2-QL, will their data be correctly processed by a
>     OWL2-QL inference engine?...
> 
>     On the other hand, this would *allow* people to use the correct datatype
>     if they want to, and/or to be compliant with OWL2-QL if they want to.
> 
>      pa
> 
>     [1] http://www.w3.org/TR/xmlschema11-2/
>     [2]
>     http://www.w3.org/TR/2009/REC-owl2-conformance-20091027/#XML_Schema_Datatypes
>     [3]
>     http://dev.w3.org/2008/video/mediaann/mediaont-api-1.0/mediaont-api-1.0.html#attributes-7
>     [4] http://www.w3.org/TR/owl2-profiles/#Entities_3
> 
>     >
>     > Felix
>     >
>     >
>     >
>     >
>     >     This hinders interoperability a tiny bit, but not as much as
>     inventing a
>     >     day and an hour for media resources for which we only know the
>     year.
>     >
>     >      pa
>     >
>     >
>     >
>     >     To all, some general remarks and conclusions
>     >
>     >     * as most metadata format are more permissive regarding dates than
>     >     xsd:dateTime, I suggest we simply use rdfs:Literal for all our
>     date
>     >     properties, and explain that it should be of the form
>     >     YYYY[-MM[-DD[Thh[:mm[:ss[.fff]]]]]]
>     >
>     >
> 
>  
> 
Received on Wednesday, 6 April 2011 09:10:00 UTC

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