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Re: Other issues - RDFa Core 1.1 IRIs vs URIRefs

From: Shane McCarron <shane@aptest.com>
Date: Thu, 10 Mar 2011 14:55:49 -0600
Message-ID: <4D793AD5.6030705@aptest.com>
To: Mischa Tuffield <mischa.tuffield@garlik.com>
CC: W3C RDFa WG <public-rdfa-wg@w3.org>, Ivan Herman <ivan@w3.org>, nathan@webr3.org
Mischa,

At the risk of confusing myself...  a request for clarification.  In 
RDFa we are concerned with both lexical space and value space of various 
things.  In particular, CURIEs require that the expansion of the lexical 
space 'foo:bar' into the value space 'http://whatever...bar' be a valid 
URI.  There are reasons for this that have to do with resource 
retrieval, follow-your-nose processing, etc.  Are you suggesting that 
the value space should be a valid IRI, that the value space should be a 
valid URI (potentially transformed from an IRI as defined in RFC 3987), 
or something else?

Just so we know where to start the discussion...

On 3/10/2011 2:38 PM, Mischa Tuffield wrote:
> Hello RDFa'ers,
>
> I was asked by Manu to summarise the email I sent to Ivan and him 
> below, for your peoples consideration. Note that, this is a "Last Call 
> comment".
>
> Quoting Manu :
>
>> Mischa, could you please summarize and send this feedback to the RDFa
>> mailing list? You can specify that it is a Last Call comment if you
>> think that it's imperative that we get this right before going into our
>> 2nd Last Call.
>>
>> RDFa WG <public-rdfa-wg@w3.org <mailto:public-rdfa-wg@w3.org>>
>>
>> It's important that the RDFa community and Working Group is aware of
>> your input and has the information it needs to make a reasonable
>> decision on the usage of IRI vs. URI vs. URI Reference.
>
> So, I am very new to working group stuff, albeit I have been playing 
> with RDF since '04 when I was a postgrad at Southampton Uni, so please 
> excuse if I get formalities wrong. I should also add that out of all 
> of the RDF serialisations I am least familiar with RDFa.
>
> I went through the RDFa Core 1.1 doc [1] and I noticed that there are 
> a number of different definitions for what a URI is in the context of 
> RDFa (see previous email in this thread with Ivan forwarded to this 
> list). The document uses the term "URI reference", which in RDF 
> Abstract Concepts terms is defined as [2], but also points to RFC's 
> 3986 [3] and RFC 3987 [4] in the same RDF Core 1.1 document - which is 
> confusing ! The question is which one is the correct definition for a 
> URI in an RDFa document?
>
> From my POV it seems that the RDFa document should be using the IRI 
> definition as per the current SPARQL work; it also seems that the RDF 
> WG is going to update the Turtle spec to talk about IRIs too. Below is 
> my motivation for saying this (cut and pasted from an email to 
> public-rdfwg mailing list at w3).
>
> Ideally, SPARQL, and the various RDF serialisations should all use the 
> same definition for what a URI is. As far as I am aware URI Refs where 
> defined in an attempt to guess what the IRI definition was going to 
> look like, and should probably be replaced by the newer IRI definition.
>
>>>> Personally i don't think that the burden of normalising URIs should 
>>>> be on applications. What is key here from my POV is the ability to 
>>>> roundtrip RDF, I will explain what I mean by this. I would like to 
>>>> be certain that if I generate new triples in my triplestore using a 
>>>> SPARQL Update query, and that I can be certain to generate valid 
>>>> RDF including those triples using the CONSTRUCT verb. Otherwise 
>>>> things just get too confusing.
>>>>
>>>> Given that SPARQL is currently in last call, it would be good to be 
>>>> able to unify what URI definitions are used in both the standard 
>>>> serialisations and in the query language. As a developer I would 
>>>> like to use only one library for generating URIs in my application, 
>>>> regardless of whether I am writing SPARQL or RDF.
>>>
>
> What I would like to avoid, is a situation whereby data can be 
> imported into a triplestore via a SPARQL Update query, which can not 
> subsequently be exported in, lets say RDFa in this case.
>
> I hope this makes sense/helps,
>
> Regards,
>
> Mischa
>
> [1] http://www.w3.org/2010/02/rdfa/sources/rdfa-core/Overview-src.html
> [2] 
> http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#dfn-URI-reference
> [3] http://www.ietf.org/rfc/rfc3987.txt
> [4] http://www.ietf.org/rfc/rfc3986.txt
>
>
> On 10 Mar 2011, at 18:25, Nathan wrote:
>
>> Ivan Herman wrote:
>>> Misha is on the RDF Working Group where we had a discussion on the 
>>> URI vs IRI issue. He reviewed the Core spec; here is his review 
>>> v.a.v this stuff.
>>> Opinions?
>>
>> "URI reference" is the thrower really, because (afaict) we don't mean 
>> URI reference ( '../foo' ) we means an "IRI compatible URI", or just 
>> "URI" or just "IRI".
>>
>> This time last week we also had URLs in the mix, it would be very 
>> good to reference either "URI" exclusively (not "URI reference") or 
>> "IRI" exclusively.
>>
>> Which one do we use? if IRI, we should say IRI everywhere.
>>
>> Best,
>>
>> Nathan
>>
>>>> Hi Ivan/Manu,
>>>> Sorry for top-posting. The relevant bit of the below thread is when 
>>>> Ivan said to me :
>>>>> Actually... there is a revision coming on RDFa. What you should 
>>>>> look at, if you can, is
>>>>> http://www.w3.org/2010/02/rdfa/sources/rdfa-core/Overview-src.html
>>>>>
>>>>> which is the editor's draft of what will soon be a 2nd last call 
>>>>> document for RDFa 1.1. It would be great if you could look at it 
>>>>> with a fresh eye with this issue in your mind...
>>>>
>>>> I have had a look at the RDFa 1.1 [1] as asked and have made an 
>>>> observation wrt to how URIs are defined in the document. If you 
>>>> feel like I should be sending this to the public-rdfa-wg mailing 
>>>> list do let me know, and/or do feel free to forward accordingly.
>>>> In short, it seems like RDFa Core 1.1 [1] uses IRIs as defined in 
>>>> RFC3987[2], URIs as per RFC3986 [3], and mentions "URI references" 
>>>> (which is the RDF world is defined as an extension to RFC2396 [4] 
>>>> in the abstract syntax document [5]) which is slightly confusing 
>>>> and maybe even a bug (from my POV anyways).
>>>>
>>>>
>>>> **So in Section 2 and Section 7.4 of the document describes URIs in 
>>>> terms of RFC3986.
>>>> **Section 3.3 - URI references - states:
>>>> "RDF solves this problem by replacing our vague terms with URI 
>>>> references."
>>>>
>>>> Note that "URI references" is not defined in this section.
>>>> and subsequently in Section 3.10 - A description of RDFa - states:
>>>> "The subject node is always either a URI reference or a blank node 
>>>> (or bnode), the predicate is always a URI reference, and the object 
>>>> of a statement can be a URI reference, a literal, or a bnode." 
>>>> which points back to Section 3.3 (as far as I can tell).
>>>> ** Section 3.8 - Compact URI Expression - states :
>>>> "RDFa allows the contraction of most URI references into a form 
>>>> called a 'compact URI expression" <-- I am not sure which URI 
>>>> reference is mentioned here.
>>>> ** Section 6 - CURIE Syntax
>>>>
>>>> Defines URIs as per RFC3987 (which are IRIs) and states :
>>>> "When expanded, the resulting URI must be a syntactically valid URI 
>>>> [RFC3987]. "
>>>> **And finally, it seems that in section 7.4 CURIE and URI 
>>>> Processing, there is pointers to the IRI spec, RFC3987 which states 
>>>> how relative URIs are resolved wrt to the documents base URI.
>>>> From my POV this is confusing, and given that SPARQL are using IRIs 
>>>> (RFC3987), and that the Turtle will probably be defined using IRIs, 
>>>> and *hopefully so will RDF/XML via RDF Abstract Syntax document 
>>>> update, I do feel strongly that RDFa should use the newer IRI 
>>>> definition in all places in the RDFa spec. (Again, please do let me 
>>>> know if you think I am wrong here).
>>>> Warmest Regards,
>>>> Mischa
>>>> [1] 
>>>> http://www.w3.org/2010/02/rdfa/sources/rdfa-core/Overview-src.html 
>>>> [2] http://www.ietf.org/rfc/rfc3987.txt [3] 
>>>> http://www.ietf.org/rfc/rfc3986.txt [4] 
>>>> http://www.ietf.org/rfc/rfc2396.txt [5] 
>>>> http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/#dfn-URI-reference
>>>>
>>>>
>>>> On 10 Mar 2011, at 09:42, Ivan Herman wrote:
>>>>
>>>>> Mischa,
>>>>>
>>>>> On Mar 9, 2011, at 19:54 , Mischa Tuffield wrote:
>>>>> <snip/>
>>>>>>>
>>>>>>>> 2) And whether or not the RDFa spec[1] is in or out of scope of 
>>>>>>>> this working group, as it is not listed in the charter as one 
>>>>>>>> of the documents which the group will be looking to update[1]? 
>>>>>>>> The reason I mention this is again, if we end up in a world 
>>>>>>>> where both SPARQL and RDF (lets say the Turtle serialisation) 
>>>>>>>> are using IRIs, developers would have to use a different URI 
>>>>>>>> encoding library for SPARQL & Turtle, from the one they would 
>>>>>>>> be using if there were to be serialising to RDFa.
>>>>>>> RDFa is certainly not in the scope of this group, there is a 
>>>>>>> separate group for that one. That being said, afaik RDFa already 
>>>>>>> uses IRIs, just like SPARQL. I explicitly copy this mail to 
>>>>>>> Manu, who is the chair of that group.
>>>>>> Thanks, and yes I am aware that Manu is the chair of that group. 
>>>>>> I need to read the entirety of the RDFa rec [1], but it seems 
>>>>>> like the only place that IRIs are mentioned are in the CURIE 
>>>>>> section [2], and the rest of the document including [2] talks 
>>>>>> about URI References and not IRIs.
>>>>> Actually... there is a revision coming on RDFa. What you should 
>>>>> look at, if you can, is
>>>>> http://www.w3.org/2010/02/rdfa/sources/rdfa-core/Overview-src.html
>>>>>
>>>>> which is the editor's draft of what will soon be a 2nd last call 
>>>>> document for RDFa 1.1. It would be great if you could look at it 
>>>>> with a fresh eye with this issue in your mind...
>>>>>
>>>>> Thanks
>>>>>
>>>>> Ivan
>>>>>
>>>>>> But, ok, I now understand that RDFa is not in the scope of this 
>>>>>> group, thanks for the clarification.
>>>>>> [1] http://www.w3.org/TR/rdfa-syntax/
>>>>>> [2] http://www.w3.org/TR/rdfa-syntax/#s_curies [3] 
>>>>>> http://www.w3.org/TR/rdfa-syntax/#sec_3.10.
>>>>>>> Note, however, that RDFa is a bit special in the sence that it 
>>>>>>> "lives" in another environment, namely HTML, which it cannot 
>>>>>>> fully control...
>>>>>> Understood.
>>>>>> Regards,
>>>>>> Mischa
>>>>>>
>>>>>>> Cheers,
>>>>>>> Ivan
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> Regards,
>>>>>>>> Mischa *goes off to look into the back-compatibility of URIRefs 
>>>>>>>> to IRIs (any pointers existing work comparing the definitions 
>>>>>>>> would be much appreciated)
>>>>>>>>
>>>>>>>> [1] http://www.w3.org/TR/rdfa-syntax/
>>>>>>>> [2] http://www.w3.org/2011/01/rdf-wg-charter#deliverables [3] 
>>>>>>>> http://www.w3.org/TR/rdfa-syntax/#T_URI_reference
>>>>>>>> ___________________________________
>>>>>>>> Mischa Tuffield PhD
>>>>>>>> Email: mischa.tuffield@garlik.com 
>>>>>>>> <mailto:mischa.tuffield@garlik.com>
>>>>>>>> Homepage - http://mmt.me.uk/
>>>>>>>> Garlik Limited, 1-3 Halford Road, Richmond, TW10 6AW
>>>>>>>> +44(0)845 652 2824 http://www.garlik.com/
>>>>>>>> Registered in England and Wales 535 7233 VAT # 849 0517 11
>>>>>>>> Registered office: Thames House, Portsmouth Road, Esher, 
>>>>>>>> Surrey, KT10 9AD
>>>>>>>>
>>>>>> ___________________________________
>>>>>> Mischa Tuffield PhD
>>>>>> Email: mischa.tuffield@garlik.com <mailto:mischa.tuffield@garlik.com>
>>>>>> Homepage - http://mmt.me.uk/
>>>>>> Garlik Limited, 1-3 Halford Road, Richmond, TW10 6AW
>>>>>> +44(0)845 652 2824 http://www.garlik.com/
>>>>>> Registered in England and Wales 535 7233 VAT # 849 0517 11
>>>>>> Registered office: Thames House, Portsmouth Road, Esher, Surrey, 
>>>>>> KT10 9AD
>>>>>>
>>>>>
>>>>> ----
>>>>> Ivan Herman, W3C Semantic Web Activity Lead
>>>>> Home: http://www.w3.org/People/Ivan/
>>>>> mobile: +31-641044153
>>>>> PGP Key: http://www.ivan-herman.net/pgpkey.html
>>>>> FOAF: http://www.ivan-herman.net/foaf.rdf
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>> ___________________________________
>>>> Mischa Tuffield PhD
>>>> Email: mischa.tuffield@garlik.com <mailto:mischa.tuffield@garlik.com>
>>>> Homepage - http://mmt.me.uk/
>>>>
>>
>
> ___________________________________
> Mischa Tuffield PhD
> Email: mischa.tuffield@garlik.com <mailto:mischa.tuffield@garlik.com>
> Homepage - http://mmt.me.uk/
> Garlik Limited, 1-3 Halford Road, Richmond, TW10 6AW
> +44(0)845 652 2824 http://www.garlik.com/
> Registered in England and Wales 535 7233 VAT # 849 0517 11
> Registered office: Thames House, Portsmouth Road, Esher, Surrey, KT10 9AD
>

-- 
Shane P. McCarron                          Phone: +1 763 786-8160 x120
Managing Director                            Fax: +1 763 786-8180
ApTest Minnesota                            Inet: shane@aptest.com
Received on Thursday, 10 March 2011 20:56:25 GMT

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