W3C home > Mailing lists > Public > public-ldp@w3.org > March 2014

Re: Practical issues arising from the "null relative URIs"-hack

From: Kingsley Idehen <kidehen@openlinksw.com>
Date: Mon, 31 Mar 2014 07:49:25 -0400
Message-ID: <53395645.1090601@openlinksw.com>
To: public-ldp@w3.org
On 3/31/14 5:51 AM, Reto Gmür wrote:
> On Fri, Mar 28, 2014 at 2:42 PM, Kingsley Idehen 
> <kidehen@openlinksw.com <mailto:kidehen@openlinksw.com>> wrote:
>     On 3/28/14 7:02 AM, Reto Gmür wrote:
>>     On Fri, Mar 28, 2014 at 12:04 AM, Kingsley Idehen
>>     <kidehen@openlinksw.com <mailto:kidehen@openlinksw.com>> wrote:
>>         On 3/27/14 4:42 PM, Reto Gmür wrote:
>>>             If you consider RFC5995 ( Using POST to Add Members to
>>>             WebDAV ) http://tools.ietf.org/html/rfc5995
>>>             you need only consider that it does not say anything
>>>             about relative URIs to understand
>>>             that because it says nothing it does exactly what we are
>>>             proposing. If you were to use
>>>             a RFC5995 compliant server to POST some Turtle with
>>>             relative URIs in it, then you'd
>>>             get exactly the LDP intended result. A turtle document
>>>             that was posted with a <> URI would refer
>>>             to the document created.
>>>         Granted. The same happens if you send an email with
>>>         text/turtle content-type. Still, a bit far fetched to see
>>>         this use as the intended design or even as to see an
>>>         established design pattern in that, imho.
>>         This is an established design pattern, that's poorly
>>         understood. Relative URIs are really a major route to taking
>>         a lot of confusion and tedium out of Linked Data exploitation.
>>     I doubt about the this being established (given that it violates
>>     RFC3986). But maybe you're right and relative URIs would be
>>     elegant and powerful. But then they should be in the RDF data
>>     model rather than having LDP breaking the abstraction. (I'm a bit
>>     afraid relative URIs in RDF might also add more confusion by
>>     people expecting the URIs so be relative to the position of the
>>     resource in the graph).
>>     What is need to create the body of a POST request using RDF
>>     toolkits with the current design:
>>       var i = new
>>     NamedResource("http://some.temporary.uri/that/must/not/be/used/elsewere/in/representation")
>>       graph.addTriple(i, RDFS.descrition, "This is the resource that
>>     will be created")
>>       ..add more triples
>>       var turtleToPost =
>>     graph.serializeAsTurtleWithBaseUri("http://some.temporary.uri/that/must/not/be/used/elsewere/in/representation")
>>     In my opinion, using this throwaway URI and hoping it doesn't
>>     escape from the context of our code is a dirty hack.
>>     If the RDF would support relative URIs things would be straight
>>     forward:
>>       var i = new NamedResource("") //Currently illegal and not
>>     supported by most toolkits!!!
>>       graph.addTriple(i, RDFS.descrition, "This is the resource that
>>     will be created")
>>       ..add more triples
>>       var turtleToPost = graph.serializeAsTurtle()
>>     Of course if RDF would support relative URIs we could use any
>>     serialization and also the problem I initially illustrated would
>>     be gone.
>>     The current question is not about using relative URIs or not but
>>     if the spec should be defined in terms of RDF or in terms of some
>>     particular serializations. The latter prevents RDF tools from
>>     being used, at least from being used  in a straight forward way.
>>     Cheers,
>>     Reto
>     To be clearer, an actual RDF graph isn't comprised or relative
>     URIs. Those URIs have to be absolute. Put differently, the final
>     product of an RDF document processing pipeline has to be a graph
>     comprised of absolute URIs.
> The problem is that with RDF tools you cannot create (unless you use a 
> throwaway URI hack as described above) what needs to be posted against 
> an LDP server.
>     There is still a subtle conflation of notation for describing an
>     RDF graph and the actual serialization that manifests when said
>     has been processed by a processor. For instance, a Turtle doc with
>     relative URIs is basically an RDF description that a processor
>     will transform into a final RDF document that's comprised of a
>     graph with absolute URIs.
>  That's why I think that relying on turtle documents with undefined 
> based-URI conflicts with the turtle spec that says: "A Turtle document 
> defines an RDF graph 
> <http://www.w3.org/TR/rdf11-concepts/#dfn-rdf-graph> composed of set 
> of RDF triple <http://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple>s"
> Cheers,
> Reto

As you can see, clearly, the habitual conflation of things in the world 
of RDF has struck again.

The abstract syntax of RDF and notations for creating RDF document 
content are being conflated yet again. Basing any RDF based spec on a 
notation (rather than abstract model) simply repeats errors from the past.

RDF specs should understand RDF and never undermine its abstract syntax. 
Likewise, Web based specs should understand HTTP URIs and their powers 
of denotation and de-reference.

Turtle specificity, is causing problems here, clearly.



Kingsley Idehen	
Founder & CEO
OpenLink Software
Company Web: http://www.openlinksw.com
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Received on Monday, 31 March 2014 11:49:47 UTC

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