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

Thu Jul 8 17:31:11 EDT 2010

Arthur, 

> The OSLC subset and generation rules result in RDF/XML documents that 
are a subset of all possible valid RDF/XML documents. 

> If we supported full RDF/XML I wouldn't need to spend time on the 
syntactic details.

This is quite deliberate.  If OSLC swallows RDF whole, we end up in a 
position where everyone consuming and providing OSLC domain specs will 
only be able to do so using full-fledged RDF/XML parsers. No consumer 
would ever be able to parse a resource with a regular XML parser, or use 
simple XML tools like xpath to extract a couple of values of interest.

This is explained in 
http://open-services.net/bin/view/Main/OSLCCoreSpecDRAFT#OSLC_Defined_Resource_Representa 
 Here's the relevant passage:

RDF/XML defines an extensive set of XML elements and attributes for 
representing an RDF data model. RDF/XML provides a lot of flexibility and 
if we allowed each OSLC workgroup to decide now to serialize OSLC 
resources to and from RDF/XML, we would require each workgroup to master 
RDF-XML, we would end-up with different serializations for each domain, 
the XML produced would not be XML-tool friendly and in the end 
interoperability would suffer. 

To ensure that the RDF/XML produced by OSLC services is uniform, easy to 
understand and as simple as possible, we define a set of step-by-step 
rules for generating the RDF/XML. We use a very limited set of RDF 
elements and attributes, the rdf:type element and attributes rdf:about, 
rdf:resource= and =rdf:nodeID.

I, for one, think this was the right direction for OSLC Core to go.

Regards,

Jim des Rivieres
Rational AMC Technical Lead

----- Forwarded by Jim des Rivieres/Ottawa/IBM on 07/08/2010 04:17 PM 
-----

From:
Arthur Ryman/Toronto/IBM at IBMCA
To:
Steve K Speicher <sspeiche at us.ibm.com>
Cc:
oslc-core <oslc-core at open-services.net>, 
oslc-core-bounces at open-services.net
Date:
07/08/2010 03:46 PM
Subject:
Re: [oslc-core] Meeting notes and using rdf:RDF as root element
Sent by:
oslc-core-bounces at open-services.net

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
Twitter | Facebook | YouTube

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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