Re: Not GRDDL, but GRDDL-like (was Re: GRDDL and OWL/XML)

Bijan Parsia wrote:
> On 20 May 2008, at 00:37, Harry Halpin wrote:
>
 
To address your worries, Bijan,  having an XSLT tranform available as a 
GRDDL transform *does not force* the GRDDL-aware agent to use the XSLT 
transform if a better or preferred alternative is available to the 
client locally. Period.

 In a nutshell, the use-case - assuming you think having RDF is useful - 
for GRDDL is that the GRDDL-aware agent, which can process RDF, may 
*not* have a local transformation for OWL 2, and therefore goes to the 
namespace document or follows a GRDDL link and downloads (using caching) 
a transformation (usually XSLT) to get out OWL 2 XML to RDF. This is 
necessarily not "silent and automatic" as the GRDDL-aware agent often 
has to explicitly enable GRDDL.

*In this case*, I believe the benefit of having an XSLT available for 
the agent outweighs the costs that have brought up. If Bijan does not 
believe that is the case, that's fine - and so I think no additional 
commentary is needed on my part, although I hope others continue to help 
Bijan. However, I would recommend that one does be clear that the 
objection to the GRDDL transformation is based on believing the 
above-mentioned scenario is not worthwhile, not on an idiosyncratic 
reading of the spec.  And having as many transforms, including locally 
installed ones that may be preferable to an XSLT one, are great for OWL 
2 and the entire SemWeb.


If this is an issue with the charter requiring a GRDDL transformation 
this should be brought up with whoever wrote the charter.


[snip]
>> Linking to a list of implementations from the namespace document 
>> using RDDL would be useful though. And having links to multiple types 
>> of transforms (distinguished by media types as mentioned by Norman 
>> Gray) could be useful as well. What is the use-case of a 
>> non-executable GRDDL transformaton?
>
> To spec what a GRDDL agent should do when encountering that namespace. 
> In the OWL case, of course, it was already obvious, but in other cases 
> it may not be.

But that spec would be human-readable list? It seems that would be 
better connected via RDDL.
>>
>> I could implemented an OWL-reasoner by writing it down an algorithm 
>> and then publishing it in HTML,
>> would this count as an implementation? I think the answer would tend 
>> to be "no."
>
> I thought the GRDDL implementation was, y'know, the GRDDL agent. I'm  
> not suggesting that people download non-executable GRDDL agents.
The GRDDL agent executes the transform, but it can not retrieve the 
transforms from a list, although Norm Gray's solution of having 
different transforms with different media types with multiple GRDDL 
links does make sense, if GRDDL-aware agents start using, say 
Javascript, as opposed to XSLT.  


Just as an OWL reasoner reasons over OWL 2, a GRDDL-aware agent executes 
a GRDDL transform. A spec list is not executable.  Just as an OWL 
reasoner written in HTML could not reason with an OWL ontology given by 
in OWL 2 XML, or one would not expect an actual OWL2 reasoner to reason 
over "OWL2 ontology" made in say, a UML authoring tool, so we would not 
expect a GRDDL aware agent to execute or do anything useful with just a 
HTML file at the end of a GRDDL transformation predicate. A human could, 
which is why a RDDL link is preferable to a GRDDL one for the spec list.

>
>> Generally, if you were selling someone an OWL 2 reasoner, they would 
>> expect code, no? Same with GRDDL.
>
> What's "GRDDL"? I mean, without a qualifier. I expect a GRDDL agent to 
> be implemented and to implement various transformations.

>
>>> This is an important point to me since various pro-GRDDL people in 
>>> the WG have argued that without an executable we have failed 
>>> according to the spec and thus failed our charter requirements. I 
>>> only endorsed the charter (and encouraged others to so endorse) with 
>>> the (weak) GRDDL requirement because I read the above spec text and 
>>> came to, what seems to me, an obvious conclusion.
>>
>> I think people have argued clearly that an executable one could be 
>> useful for RDF-consuming GRDDL-enabled agents that would like to 
>> "glean" some information from OWL 2.
>
> *An* executable, not a silently auto-downloadable one.

As I have stated about five times before, it does not have to "silently, 
auto-downloadable." Local policy could enable the download, and in fact, 
most GRDDL implementations seem to be able to turn GRDDL "off and on" 
with command-line options. Furthermore, if a locally installed transform 
was available, GRDDL would probably not be used.


>> That's a use-case that I have yet to see an argument against that 
>> caching and warnings about normativity would not address.
>
> That's not a use case, that's a deployment scenario. You start with 
> the presumption that GRDDL-enabled agents will not bundle transforms.
>
> After all, they don't need to *DO* the coding themselves! Someone can 
> write a free XSLT transform and the GRDDL agent author can download it.

But where from? The obvious place is the namespace document for GRDDL.

>>> From a marketing perspective, it feels like a bait and switch. I 
>>> feel like I did due diligence and now am sandbagged. Proper specs 
>>> *cannot* require people to interview members of the community to 
>>> determine what conforming behavior is. That defeats the point!
>> No-one else in the community has ever brought up the point that the 
>> GRDDL transformation could be non-executable.
>
> This is a weakness on your part, not a strength. It's a 
> straightforward reading of the spec.
>
> Part of the point of specs is to codify *in the spec* the understanding.
>

It could also be an idiosyncratic reading of the spec whose use cases I 
have consistently would be better served by human-readable explanation 
at the namespace document and serving a RDDL file with links to other 
implementations.

> One thing I'm trying to convey is that I thought I *was* part of the 
> GRDDL community, broadly construed. But I guess I'm not and people 
> with my sorts of concerns and perspectives are not. (That's fine! 
> Nothing morally wrong with that. Just be aware that it limits adoption.)

We are all part of the community, both GRDDL and wider Semantic Web 
community, and trying to understand each other's needs I hope!

>
>> Thus, I think your reading of the specification is unique. I am glad 
>> you have brought this up, as no-one has thought this through before, 
>> and it is an intelligent if unusual point.
>>
>> I think if you or others do not want an executable GRDDL 
>> transformation, or object to a RDF translation of OWL2/XML to RDF, 
>> that's fine. It is clear you believe an executable GRDDL is 
>> unnecessary or harmful and there is no reason to address 
>> RDF-consuming agents that may not have OWL2XML local transforms. I 
>> would be interested if other members of the OWL2 WG also think this 
>> is the case.
>
> Some do, some do not. I'm still unclear why this is a *use* case.

See first point.

> Cheers,
> Bijan.
>

Received on Tuesday, 20 May 2008 14:02:40 UTC