Re: Interaction model vs data model

On 24 Jan 2013, at 05:36, Eric Prud'hommeaux <eric@w3.org> wrote:

> * Arnaud Le Hors <lehors@us.ibm.com> [2013-01-23 17:08-0800]
>> There seems to be some confusion in the discussions as to what we can do 
>> and what we can't which comes from different views of what LDP is about.
>> 
>> Discussing whether LDPCs are a subclass of LDPRs, Henry wrote [1]: "they 
>> are not, since POSTing a Graph on an LDPR is very different from POSTing 
>> on an LDPC, and since RDF is a logical vocabulary that does not work with 
>> the concept of method overloading. "
>> 
>> I have to admit not to understand this statement at all and, maybe it's 
>> just me but, I actually believe that clarifying this might help us a great 
>> deal with the ongoing discussions around the interaction and data models.
>> 
>> RDF doesn't have the concept of methods, so it certainly doesn't have the 
>> concept of method overloading, but this merely concerns the data model. I 
>> don't understand why this would prevent us from defining different ways of 
>> handling HTTP verbs depending on the type of LDP resource we deal with - 
>> an LDPR or LDPC. I would say this only concerns the interaction model and 
>> the RDF data model doesn't prevent us from doing so.

Thanks for bringing this up Arnaud. 

> 
> I think that we are making only trivial statements about type if one
> can't predict some opperational behavior from that type. The most
> practical type I can imagine is one that tells me if POSTing RDF will
> append it (LDPR) or submit a new element to a container (LDPC).  To
> that end, I think that LDPC and LDPR are sibling resources with some
> common ancestor. It's probably worth identifying that ancestor as it
> has a few properties common to both LDPCs and LDPRs, namely that GET
> gets you some relevant RDF and that it's defined by LDP.


Exactly :-) Thanks for making this clear. 

> 
> 
>> For what it's worth, section 5.2.1 of the LDP spec [2] states that "A 
>> Linked Data Platform Container must also be a conformant Linked Data 
>> Platform Resource." I've always read that as meaning that an LDPC is an 
>> LDPR.
>> 
>> What am I missing?

I think it is possible that as things change and as we formalise things, 
we notice that there are incompatibilities in terms of operational 
behavior between different types of things that we had not noticed earlier. 
It is pretty tricky. We may even find that new types of things start
emerging,...

>> 
>> [1] 
>> http://www.w3.org/2012/ldp/wiki/index.php?title=ISSUE-37&oldid=1998#Are_LDPCs_subclasses_of_LDPRs.3F
>> [2] http://www.w3.org/TR/2012/WD-ldp-20121025/#general-1
>> --
>> Arnaud  Le Hors - Software Standards Architect - IBM Software Group
> 
> -- 
> -ericP
> 



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