W3C home > Mailing lists > Public > public-gld-wg@w3.org > January 2012

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

From: Stasinos Konstantopoulos <konstant@iit.demokritos.gr>
Date: Mon, 30 Jan 2012 15:02:27 +0200
Message-ID: <CANaM+WEmTQAAGXwCteuHeHhu-sUjcq-Ndj-UPCiPTsWz3Q+QnA@mail.gmail.com>
To: John Erickson <olyerickson@gmail.com>
Cc: Government Linked Data Working Group WG <public-gld-wg@w3.org>
John, hi.

The original ISSUE-3 email states representing "sometime in the 1970s
or '80s" as a requirement. Just replace my birthdate with a documents'
creation date, if that helps.

s


On 30 January 2012 14:45, John Erickson <olyerickson@gmail.com> wrote:
> 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 13:03:11 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 25 June 2013 15:04:56 UTC