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Re: Serializing datetime

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Tue, 31 Jul 2012 17:23:17 +0100
Message-ID: <50180675.6020401@epimorphics.com>
To: public-rdf-dawg-comments@w3.org, David Booth <david@dbooth.org>


On 31/07/12 17:06, David Booth wrote:
> Hi Andy,
>
> I am satisfied with this resolution provided that "Advice on canonical
> datetime values" is added to the wish list for consideration in the next
> version:
> http://www.w3.org/2009/sparql/wiki/Future_Work_Items
>
> It certainly is possible to convert, but one important point of
> standardization is to reduce the amount of conversion that is needed
> when transferring data from one system to another.

Standards build on other standards.

The canonical representation of datetime is already defined by:

http://www.w3.org/TR/xmlschema11-2/#vp-dateTimeCanRep

coupled with the requirements of RDF datatypes.  Surely this is an RDF 
issue, not SPARQL specific?

If the input data uses a specific timezone, many people will expect that 
to be preserved.  Maybe the whole application is used in one timezone.


Value based matching is a feature of SPARQL 1.0 and can be achieved with 
FILTER and XSD:

"2012-07-31T17:16:00+01:00"^^xsd:dateTime
=
"2012-07-31T16:16:00Z"^^xsd:dateTime

The relationship of
"2012-07-31T17:16:00+01:00"^^xsd:dateTime
and
"2012-07-31T16:16:00"^^xsd:dateTime
is indeterminate
and
"2012-07-31T17:16:00+01:00"^^xsd:dateTime
 >
"2012-07-30T16:16:00"^^xsd:dateTime'

(the 14 hour rule).


	Andy

>
> Thanks,
> David
>
>
> On Tue, 2012-07-31 at 09:05 +0100, Andy Seaborne wrote:
>> David,
>>
>> Thank you for your comment on serializing datetime values.
>>
>> As noted in the response to your comment on "Serializing xsd:decimal,
>> xsd:float, xsd:double", SPARQL reuses the body of work for XSD and
>> XQuery/XPath functions and operators.  The rules for operations on
>> datetimes derive from that work and this includes comparing datetime
>> values.  Support is also now to be found in many programming languages.
>>
>> An implementation is free to provide custom function that converts
>> between timezones; XQuery/XPath does not itself provide such a function.
>>
>> The working group is not planning to make any changes in this area.
>>
>> I would be grateful if you reply to this message to confirm that the
>> working group has responded to your comment.
>>
>> Yours, on behalf of the SPARQL Working Group,
>>
>>       Andy
>>
>> On 20/07/12 16:21, David Booth wrote:
>>> I have also noticed that it is a hassle trying to compare datetime
>>> values from two different SPARQL servers, because the same datetime may
>>> be written with different timezone offsets.  This is less vexing than
>>> xsd:decimal serializations, because at least timezone offsets are
>>> information preserving, but still it makes comparisons more difficult
>>> than they otherwise need to be.
>>>
>>> I think the WG should consider defining a default datetime format (such
>>> as UTC or zero timezone offset) that SHOULD be use, while allowing
>>> servers to make this a configurable option.
>>>
>>> I assume it is too late in the WG process to consider this for SPARQL
>>> 1.1, so please add this to the wish list for the next version.
>>>
>>> Thanks!
>>>
>>
>>
>
Received on Tuesday, 31 July 2012 16:23:49 GMT

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