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Re: ISSUE-3 (DTF): Date and Time Format

From: John Erickson <olyerickson@gmail.com>
Date: Mon, 30 Jan 2012 07:45:30 -0500
Message-ID: <CAC1Gg8TRkw8Uc4R4ZP3x5fBZyY9SMU8dQAVL1-3mhpFTpJHVYQ@mail.gmail.com>
To: Stasinos Konstantopoulos <konstant@iit.demokritos.gr>
Cc: Government Linked Data Working Group WG <public-gld-wg@w3.org>
RE Stasinos' comments, I'd like to remind those "listening" to this
date thread that this is about catalog metadata, NOT metadata within a
dataset.

Thus we should NOT be considering examples including e.g. birth dates
in this discussion.

+1 to CLOSING this discussion by recommend xad:date but permitting
text literals... pax vobiscum ;)

On Mon, Jan 30, 2012 at 7:30 AM, Stasinos Konstantopoulos
<konstant@iit.demokritos.gr> wrote:
> All, hi.
>
> just some random ranting on the possiblity of more flexible
> underspecified dates than what has been proposed so far. I am towards
> recommending Approach 3 myself, although Approach 1 has the merit of
> perfectly fitting the current practice of using the first day of the
> month to mean any time during the month.
>
> Best,
> Stasinos
>
>
>
> Let us say that we want to use the property gld:birthDate to assert
> that http://konstant.gr/#stasinos was born between Aug 15th and Sep
> 15th, 1973, but we are unable to provide a specific date.
>
>
> Aproach 1
>
> We define one specificity property for each property that ranges over
> dates that can potentially be underspefied. This property ranges over
> xsd:duration and means that the value of the original property should
> be understood as an unknown xsd:date instance that lies within the
> interval starting on the date shown by the original property and
> lasting for the duration shown by the specificity property.
>
> In our example we define
>  gld:birthDateSpecificity rdfs:range xsd:duration
> and specify that, if present, the value of gld:birthDate should be
> understood as an unknown xsd:date instance that lies within the
> interval starting on the date shown by gld:birthDate and lasting for
> the duration shown by gld:birthDateSpecificity:
>
> <http://konstant.gr/#stasinos>
>   gld:birthDate "1973-08-15"^^xsd:date ;
>   gld:birthDateSpecificity "P1M"^^xsd:duration .
>
> Pros:
> - It is simple to explain and populate.
> - It is consistent with current practice of using midnight of the
>  first day of the month (year) to mean an unknown date during that
>  month (year). We can make explicit that a given "1973-01-01" value
>  is actual meant to mean "sometime during 1973" WITHOUT retracting
>  any statements, but by adding a specificity statement of
>  "P1Y"^^xsd:duration.
>
> Cons:
> - It requires a new property for each property that we want to treat.
> - It distributes a meaning over two properties that are not nested
>  within the same pattern, but are at the same level as other, related
>  properties of the same resource.
>
>
> Aproach 2
>
> Both cons above can be treated by introducing blank nodes (shudders)
> or genids or whatever name is more palatable as values of
> gld:birthDate. Such nodes would have properties of their own,
> restricting the range of possible concrete values they can assume:
>
> <http://konstant.gr/#stasinos> gld:birthDate [
>   rdf:type gld:underSpecifiedDate ;
>   gld:startDate "1973-08-15"^^xsd:date ;
>   gld:specificity "P1M"^^xsd:duration
> ] .
>
> We can, if so inclined, give more formal rigour by making explicit
> that gld:underSpecifiedDate is an instance inside an inteval and not
> the whole interval:
>
> <http://konstant.gr/#stasinos> gld:birthDate [
>   rdf:type gld:date ;
>   gld:within [
>     gld:dateInterval
>     gld:startDate <http://dates.org/1973/08/15> ;
>     gld:specificity "P1M"^^xsd:duration
>   ]
> ] .
>
> Note that the range of gld:birthDate is now a resource (since it has
> properties of its own) so this breaks compatibility with using
> xsd:date values when the date is known exactly. Exact dates would have
> to either be date URIs or be blank nodes with a data property ranging
> over xsd:date:
>
> <http://konstant.gr/#stasinos>
>  gld:birthDate <http://dates.org/1973/09/02> .
>
> or
>
> <http://konstant.gr/#stasinos>
>  gld:birthDate [
>    rdf:type gld:date ;
>    gld:hasValue "1973-09-02"^^xsd:date ] .
>
>
> Pros:
> - Relatively simple to explain
> - It defines a handful of types and properties that can be used for
>  any property that ranges over dates. gld:date does not need to be a
>  new type, but can be the type of any existing date URI schema.
> - It collects all the triples about the underspecified date under
>  single reosurce
>
> Cons:
> - Harder to populate than Approach 1
> - It breaks compatibility with current practice, even for fully known
>  dates.
>
>
> Approach 3
>
> We define gld:birthDate as a datatype property that ranges over the
> union of xsd:date and gld:underspecifiedDate. gld:underspecifiedDate
> is a simple datatype, derived by restricting xsd:string to:
>  DD(SS)?
> where DD is the lexical space of xsd:date and SS is the lexical space
> of xsd:duration.
>
> Semantics is start date and specificity as above. SS is optional and,
> if missing, defaults to "P1D" (one day).
>
> Examples:
>
> <http://konstant.gr/#stasinos>
>  gld:birthDate "1973-08-15P1M"^^gld:underspecifiedDate .
>
> The following values are equal (although not identical, so functional
> properties can have only one):
>  "1973-09-02P1D"^^gld:underspecifiedDate .
>  "1973-09-02"^^gld:underspecifiedDate .
>  "1973-09-02"^^xsd:date .
>
> The following values are not equal, as per the definition of
> xsd:duration that states that no relationship exists between months
> and days:
>
>  gld:birthDate "1973-08-15P1M"^^gld:underspecifiedDate .
>  gld:birthDate "1973-08-15P31D"^^gld:underspecifiedDate .
>
> Pros:
> - Relatively simple to explain and populate
> - It maintains compatibility with xsd:date, although inconsistent with
>  the practice of using midnight of the first day of the month (year)
>  to mean an unknown date during that month (year), as all xsd:date
>  values are interpreted as exact dates.
>
> Cons:
> - Harder to index, as "1973-08-15P1M", "1973-08-15P15D", and
>  "1973-08-15" are all different values. Searching for all documents
>  related to "1973-08-15" requires full-text search with globs; not
>  a hard requirement (e.g., Solr does prefix* globs), but less
>  efficient than searching for exact values.
>
>
>
> Approach 4
>
> One, rather cumbersome, solution using existing OWL 2 constructs is to
> not make a direct gld:birthDate assertion, but instead restrict the
> possible values of this property for this resource, if ever
> discovered:
>
> ClassAssertion(
>  DataAllValuesFrom(
>    gld:birthDate
>    DatatypeRestriction(
>      xs:dateTime
>      xsd:minInclusive "1973-08-15T00:00:00Z"^^xsd:dateTime
>      xsd:maxExclusive "1973-09-16T00:00:00Z"^^xsd:dateTime ))
>  <http://konstant.gr/#stasinos> )
>
> and as RDF triples:
>
> <http://konstant.gr/#stasinos> rdf:type
>  [ rdf:type owl:Restriction ;
>    owl:onProperty gld:birthDate ;
>    owl:allValuesFrom
>      [ rdf:type rdfs:Datatype ;
>        owl:onDatatype xsd:dateTime ;
>        owl:withRestrictions (
>          [ xsd:minInclusive "1973-08-15T00:00:00Z"^^xsd:dateTime ]
>          [ xsd:maxExclusive "1973-09-16T00:00:00Z"^^xsd:dateTime ] )
>      ]
>  ] .
>
> The use of midnight values of xsd:dateTime instead of xsd:date is
> mandated by the fact that xsd:date does not permit the
> xsd:minInclusive/xsd:maxExclusive restriction facets.
>
> This is, obviously, not something any sane person would suggest that
> GLD recommends, but goes to show that it is very well possible to
> formalize a human-readable underspecified date format by transforming
> to equivalent OWL 2 data.
>



-- 
John S. Erickson, Ph.D.
Director, Web Science Operations
Tetherless World Constellation (RPI)
<http://tw.rpi.edu> <olyerickson@gmail.com>
Twitter & Skype: olyerickson
Received on Monday, 30 January 2012 12:46:08 UTC

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