W3C home > Mailing lists > Public > public-lod@w3.org > November 2010

Re: 200 OK with Content-Location might work

From: Kingsley Idehen <kidehen@openlinksw.com>
Date: Sun, 07 Nov 2010 11:47:55 -0500
Message-ID: <4CD6D83B.2060806@openlinksw.com>
To: John Sheridan <johnlsheridan@yahoo.com>
CC: Niklas Lindström <lindstream@gmail.com>, Ian Davis <me@iandavis.com>, public-lod@w3.org
On 11/7/10 10:07 AM, John Sheridan wrote:
> Niklas,
> In general I am supportive of your and Ian's thinking. 200 OK with
> Content-Location might work.
> However, three points from my perspective:
> 1) debating fundamental issues like this is very destabilising for those
> of us looking to expand the LOD community and introduce new people and
> organisations to Linked Data. To outsiders, it makes LOD seem like its
> not ready for adoption and use - which is deadly. This is at best the
> 11th hour for making such a change in approach (perhaps even 5 minutes
> to midnight?).


We must put concept (and value prop. demonstration) before mechanics.

This mailing list isn't private, it has google-juice, and its an early 
point of call re. Linked Data.

> 2) the 303 pattern isn't *that* hard to understand for newbies and maybe
> even helps them grasp LOD.

And when the dust settles, it will remain. Ian's efforts will have the 
net effect of a new option, no more no less. Just an option.

Loose coupling (non authoritative) resource descriptors (information 
resources) are going to be important forever.

Pubby and Virtuoso have always demonstrated the above. In the beginning 
Pubby (Linked Data Document middleware) was in Berlin and the DBpedia 
Quad Store in Burlington, MA. Today, via Virtuoso we still have all 
sorts of options re. location of the Linked Data Docs relative to the 
actual DBpedia Quad Store. This kind of flexibility is vital to Linked 
Data in general.

> Making the difference between NIRs and IRs so
> apparent, I have found to be (counter-intuitively) a big selling point
> for LOD, when introducing new people to the paradigm. Let's not be too
> harsh on 303 - it does make an important distinction very clear for new
> adopters and, in my experience, it seems to be an approach new people
> grok quite quickly and easily.

The Descriptor Document URL and  Subject Name dichotomy is intuitive. It 
does help new users and anyone else that's "concept comprehension 
oriented" re. Linked Data.
> 3) I see much to commend in what Ian suggests, in practical terms. If
> the community is going to move in that direction what we need is a clear
> roadmap. An alternative pattern (say, 200 OK plus Content-Location)
> needs to be (*very* quickly) alighted upon and then used in practice. We
> would have to reconcile ourselves to the 303 pattern and the
> alternative, operating side-by-side, for some period of time (years?).

This is just an option, it can never be more than an option.

> Only once there is some breadth of usage, should the community seek to
> deprecate the use of 303s.

I don't think 303 indirection can be depreciated. We just have another 
option that full leverages the self-describing nature of RDF resources. 
The mechanism for disambiguating Entity (Non Information Resource) Name 
and Descriptor (Information Resource) Address is adjudicated by the data 

> If this is a pattern the community wishes to
> change, we have to gradually evolve our way to something different. We
> can't just leap.

An optional evolutionary path. This is something platforms you handle 
without distraction to users.

> Hope these thoughts help,

Very much so :-)

> John.
> On Sun, 2010-11-07 at 14:42 +0000, John Sheridan wrote:
>> One use-case that we have with the Linked Data work for UK Government,
>> is where we have a URI for a NIR at one (notionally more stable) domain
>> which 303s to an IR at a different (less stable, organisationally
>> orientated) domain.
>> Often the NIR URI is something like
>> http://{something}.data.gov.uk/id/something whereas the IR is on an
>> organisation's own website.
>> We do this because organisations in the public sector are unstable and
>> subject to continual change (creation, merger, abolition) whereas the
>> government as a whole is very stable.
>> To give an example, the Open Government Licence (for the NIR of the
>> licence) is http://reference.data.gov.uk/id/open-government-licence
>> which 303s to
>> http://www.nationalarchives.gov.uk/doc/open-government-licence/ (the IR
>> of the current licence text, currently published by The National
>> Archives, with HTML and RDF representations selected through conneg)
>> We are looking at a similar pattern for local authorities. Each Council
>> would have a NIR URI at (something like)
>> local.data.gov.uk/id/{local-council-identifier} which would 303 to IR
>> about that Council on the Council's own website.
>> Our thinking is that the {something}.data.gov.uk URI is more likely to
>> survive machinery of government changes, but the organisation
>> responsible for (say) the Open Government Licence is always going to
>> want to publish the IR about that on its own website, and should be
>> encouraged to do so.
>> The 303 pattern helps enable this pattern, which fits well in general
>> with some of the challenges on Linked Data in the public sector.
>> I would like to understand a little better how Ian's proposal maps to
>> this use case.
>> Grateful for comments,
>> John.
>> On Sun, 2010-11-07 at 12:11 +0100, Niklas Lindström wrote:
>>> +1 indeed. Content-Location has definitely been overlooked. During
>>> conneg, it is used to differ between a resource and its
>>> representation(s), which are obviously different resources (well, not
>>> necessarily the same). This distinction could certainly be enough to
>>> remove the fundamental need for 303:ing on NIR:s (provided consensus
>>> and some formal resolution).
>>> (I pondered on a similar issue in
>>> <http://lists.w3.org/Archives/Public/public-rdf-in-xhtml-tf/2010Feb/0007.html>,
>>> regarding the identity of fragments. Perhaps that discussion would be
>>> worth revisiting again in light of this?)
>>> Best regards,
>>> Niklas
>>> On Fri, Nov 5, 2010 at 5:55 PM, Nathan<nathan@webr3.org>  wrote:
>>>> Mike Kelly wrote:
>>>>> http://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-12#page-14
>>>> snipped and fuller version inserted:
>>>>    4.  If the response has a Content-Location header field, and that URI
>>>>        is not the same as the effective request URI, then the response
>>>>        asserts that its payload is a representation of the resource
>>>>        identified by the Content-Location URI.  However, such an
>>>>        assertion cannot be trusted unless it can be verified by other
>>>>        means (not defined by HTTP).
>>>>> If a client wants to make a statement  about the specific document
>>>>> then a response that includes a content-location is giving you the
>>>>> information necessary to do that correctly. It's complemented and
>>>>> further clarified in the entity body itself through something like
>>>>> isDescribedBy.
>>>> I stand corrected, think there's something in this, and it could maybe
>>>> possibly provide the semantic indirection needed when Content-Location is
>>>> there, and different to the effective request uri, and complimented by some
>>>> statements (perhaps RDF in the body, or Link header, or html link element)
>>>> to assert the same.
>>>> Covers a few use-cases, might have legs (once HTTP-bis is a standard?).
>>>> Nicely caught Mike!
>>>> Best,
>>>> Nathan



Kingsley Idehen	
President&  CEO
OpenLink Software
Web: http://www.openlinksw.com
Weblog: http://www.openlinksw.com/blog/~kidehen
Twitter/Identi.ca: kidehen
Received on Sunday, 7 November 2010 16:48:26 UTC

This archive was generated by hypermail 2.4.0 : Thursday, 24 March 2022 20:29:51 UTC