Re: More Work on iCalendar RDF Schema

ok, then, the DAML work looks a lot like Aaron's formulation, and fits
with Michael's use of xml datatypes in the hybrid schema.

The thing I particularly like about the DAML work is that it leaves room
for using literals as representations of datatypes as well, i.e.


[[
As a nod to backward compatability, literals that occur outside this
sort of construction are interpreted as any of the XML Schema Datatype
values with this lexical representation. These values are mostly
unusable unless some typing information is available, such as a range
for a property. 
]]
(http://www.daml.org/2001/03/reference.html)

Dan's just pointed out to me something I hadn't really grasped about the
meaning of this paragraph - namely that it supports both

<Age rdf:value"28" /> (Age is a class)
and 
<age>28</age> (age is a property)

in the latter case you'd need somethnig like


<rdf:Property
	rdf:about=http://test/age"
	rdfs:label="age" 
	rdfs:comment="An age">
	<rdfs:range rdf:resource="&xsd;Integer"/>
</rdf:Property>

in the schema to make the age literal value meaningful.

This leaves open the possibility for people to use a literal construct
for datetimes if they so wish.


we still have the problem that
[[
However, unlike iCalendar rfc 2445, xml datatypes use UTC offsets for
timezones.
]]

...I said in a previous email.


[[
The form of date and time with UTC offset MUST NOT be used.
]] 
(http://www.imc.org/rfc2445)


We might be able to overcome this. RFC 2445 allows a UTC offset property
if there's a utc timezone Z datetime.

[[ 
Purpose: This value type is used to identify properties that contain
   an offset from UTC to local time.
]]
(http://www.imc.org/rfc2445)

so a UTC-offset timezone string would be equivalent in meaning to an RDF
2445 datetime with a UTC property.

There is also the issue that xml schema datatypes and icalendar
datatypes may use different substs of iso 8601:

[[
The "DATE-TIME" data type is used to identify values that contain a
   precise calendar date and time of day. The format is based on the
   [ISO 8601] complete representation, basic format for a calendar date
   and time of day. 
]]
(http://www.imc.org/rfc2445)


[[
The primitive datatypes duration, dateTime, time, date, gYearMonth,
gMonthDay, gDay, gMonth and gYear use lexical formats inspired by [ISO
8601]. This appendix provides more detail on the ISO formats and
discusses some deviations
from them for the datatypes defined in this specification. 
]]
(http://slow1.w3.org/TR/xmlschema-2/#isoformats)

this is just a note to flag further work - I haven't investigated what
'inspired by' might mean in this context yet.


cheers

Libby




On Tue, 26 Jun 2001, Dan Brickley wrote:

> 
> (+cc: Brian McBride, RDF Core WG co-chair)
> 
> On Tue, 26 Jun 2001, Libby Miller wrote:
> 
> > > > route we chose to add this feature. This does seem like a
> > > > somewhat tricky issue you're facing.  The best way I can think
> > > > of is something like:
> > > >
> > > > 	<dtstart><DateTime rdf:value="W3CDTF goes here" /></dtstart>
> > > >
> > > > What do you think?
> > >
> >
> > this would be a good option - but I prefer Jan's _if_ this work  is
> > likely to happen reasonably soon!
> 
> In the RDF Core WG we are about to start opening up issues relating to the
> RDF Schema Specification. Input from real-world applications of RDF, such
> as rdf-calendar, is of great value: it helps us prioritise our work, so we
> can focus on removing obstacles to RDF deployment. It also provides us
> with test cases material, so we can have some metrics for judging success.
> >
> > what d'you reckon Jan? Is there anything I/we can do to speed this
> > up? (these issues keep cropping up) I've got project time I could use
> > to look at this issue.
> 
> The most detailed work on this to date has been in DARPA's DAML
> initiative. See http://www.daml.org/2001/03/daml+oil-index.html for
> recent specs which include a proposal for doing datatyping in RDF, or
> http://www.w3.org/RDF/Interest/ -> http://lists.w3.org/Archives/Public/www-rdf-logic/
> for the RDF-Logic mailing list where many of the DAML folk hang out.
> 
> The reference description of March's DAML+OIL spec has this to say on
> datatyping of literals using XML schema datatypes:
> 
> http://www.daml.org/2001/03/reference.html#Values
> [[
> Datatype values are written in a manner that is valid RDF syntax, but
> which
> is given a special semantics in DAML+OIL.
> The preferred method is to give a lexical representation of the value as a
> string, along with an XML Schema datatype that is
> used to provide the type of the value as well as the parsing mechanism to
> go from the string to the value itself.
> The XML Schema datatype is the rdf:type of the value, and the
> lexical representation is the rdf:value of the value.
> So the decimal 10.5 could be input as
> <xsd:decimal rdf:value="10.5">
> provided that xsd was defined as the URI of the XML Schema
> Datatype specification.
> As a nod to backward compatability, literals that occur outside this sort
> of construction are interpreted as any of the XML Schema Datatype values
> with this lexical representation.  These values are mostly unusable unless
> some typing information is available, such as a range for a property.
> The question of whether any XML Schema datatype can be used in such
> constructions, or whether only certain XML Schema dataypes can be so used
> (such as only the predefined datatypes), remains open.
> ]]
> 
> > Are there any RDF processing issues you know of about this change?
> >
> > what does everyone think?
> 
> I suggest trying to implement according to the DAML+OIL proposal, and
> letting the RDF Core WG know if it works, or doesn't work, for calendar
> applications. This will provide useful fodder for RDF Core discussions
> when we get to this topic.
> 
> Dan
> 
> 
> >
> > Libby
> 
>

Received on Tuesday, 26 June 2001 10:41:24 UTC