[oslc-core] Meeting notes and using rdf:RDF as root element

[Arthur Ryman]

Steve,

I am not referring to the use of <rdf:RDF> element since that is a part of 
RDF/XML. I am referring to the exclusion of those features of RDF/XML that 
are not part of the OSLC subset. The OSLC subset and generation rules 
result in RDF/XML documents that are a subset of all possible valid 
RDF/XML documents. There is no guarantee that when I serialize an RDF 
graph using some toolkit that the result will fall within the subset 
defined by OSLC.

For example, the document might contain multiple <rdf:Description> 
elements for the subject nodes instead of "inlining" the triples under 
some main subject node, or a subject node might not use the expected 
rdf:type abbreviation if it had multiple types. There are other features, 
such as rdf:parseType="Resource" and rdf:parseType="Collection" that are 
not in the OSLC subset, but that might get generated. Those are simply 
abbreviations that produce more compact and readable documents, but that 
are not in the OSLC subset. A serializer could generate them.

On a related thought, consider the issue of "enforcing" conformance to the 
OSLC subset.

Currently, the OSLC subset is described implicitly, i.e. as the result of 
applying the representation rules. This means there is no programmatic way 
to check conformance of an RDF/XML document with the OSLC rules. However, 
I don't think it would be a good use of our time to create an OSLC 
validator. We don't want to enshrine this subset since it's very likely to 
change (and probably coincide with RDF/XML eventually).

Here's a real-world example. Today I reviewed a design for calendar 
events, based on the RDF representation of the iCal standard. Here's a 
sample RDF/XML representation:

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
        xmlns:jc="http://jazz.net/xmlns/prod/jazz/calendar#" xmlns="
http://www.w3.org/2002/12/cal/icaltzd#"
        xmlns:foaf="http://xmlns.com/foaf/0.1/">
        <VCalendar>
                <jc:calendar_owner rdf:parseType="Resource">
                        <foaf:mbox rdf:resource="mailto:user at local.net" />
                        <foaf:nick>user</foaf:nick>
                </jc:calendar_owner>
                <component>
                        <Vevent>
                                <jc:ownerResource rdf:parseType="Resource"
>
                                        <foaf:nick>user</foaf:nick>
                                </jc:ownerResource>
                                <dtstart rdf:datatype="
http://www.w3.org/2002/12/cal/icaltzd#dateTime">2010-01-01T09:00:00Z</
dtstart>
                                <dtend rdf:datatype="
http://www.w3.org/2002/12/cal/icaltzd#dateTime">2010-03-31T18:00:00Z</
dtend>
                                <transp>TRANSPARENT</transp>
                                <rrule rdf:parseType="Resource">
                                        <freq>WEEKLY</freq>
                                        <byday>MO,TU,WE,TH,FR</byday>
                                </rrule>
                        </Vevent>
                </component>
        </VCalendar>
</rdf:RDF>

This is valid RDF/XML. It uses standards like iCal and FOAF. However, it 
is invalid wrt to OSLC subset. Note the use of rdf:parseType="Resource". 
Also note the use of the iCal dateTime datatype, which is not on the 
approved list of datatypes.  I don't think it's a good use of anyone's 
time to try to hammer this into a shape that matches the OSCL subset. I'd 
rather just focus on the data and interface. If we supported full RDF/XML 
I wouldn't need to spend time on the syntactic details.

Regards, 
___________________________________________________________________________ 

Arthur Ryman, PhD, DE


Chief Architect, Project and Portfolio Management

IBM Software, Rational

Markham, ON, Canada | Office: 905-413-3077, Cell: 416-939-5063
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From:
Steve K Speicher <sspeiche at us.ibm.com>
To:
Dave <snoopdave at gmail.com>
Cc:
oslc-core <oslc-core at open-services.net>
Date:
07/08/2010 02:39 PM
Subject:
Re: [oslc-core] Meeting notes and using rdf:RDF as root element
Sent by:
oslc-core-bounces at open-services.net



> > Furthermore, when I try to generate RDF using
> > the toolkit, it will not conform to the OSLC subset so I'll have to 
write
> > my own serializer. We are therefore in the paradoxical situation of
> > embracing RDF as our data model yet making life more difficult for
> > implementers that want to use RDF toolkits.
> 
> This could be a real issue and probably warrants some testing with
> Jena and other RDF serializers. Can anybody comment in this issue?
> 

I inquired on this to a team that I know has been using RDF/XML (Jena) for 

some time, they said they didn't have this issue.  In fact, they had to do 

some unnatural acts to remove <rdf:RDF> root element, so adding that back 
has made things much simpler.

- Steve


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