Re: PROV-ISSUE-78 (contexts-and-provenance-uris): multiple contexts and provenance-uris [Accessing and Querying Provenance]

Hello Luc,

On Tuesday 23 August 2011 00:50:36 Provenance Working Group Issue Tracker 
wrote:
> PROV-ISSUE-78 (contexts-and-provenance-uris): multiple contexts and
> provenance-uris [Accessing and Querying Provenance]
> 
> http://www.w3.org/2011/prov/track/issues/78
> 
> Raised by: Luc Moreau
> On product: Accessing and Querying Provenance
> 
> 
> We seem to allow for multiple context-uris and provenance-uris to be
> provided. I am fine with this.
> 
> But don't we want to be able to say, for instance:
> 
>  context-uri1  provenance-uri1
>  context-uri1  provenance-uri2
>  context-uri2  provenance-uri3
>  context-uri2  provenance-uri4
> 
> Do we want to be able to express this?

I would like to see that, where possible.

> Can this be expressed?

It depends. You have to distinguish two cases here: 1.) the HTTP Link header 
field (Sec.3.1 in the PAQ document) and 2.) the HTML link element (Sec.3.2).

We are currently discussing this [1,2].

The situation is as follows: For the HTTP Link based mechanism we have the 
anchor parameter with which it is possible explicitly associate a context-URI 
with a provenance-URI. For the HTML link based mechanism there is nothing 
equivalent. That's why Section 3.2 introduces an "anchor" (name is subject to 
discussion) link relation type (in addition to the "provenance" link relation 
type). Primarily for consistency (as far as I understand) an equivalent link 
relation type "anchor" has been introduced in Sec.3.1 for the HTTP Link based 
mechanism. The discussion here is (see the first Issue in Sec.3.1) whether we 
use that additional "anchor" link relation type for the HTTP case (which would 
not allow us to express what you ask for) or if we use the anchor parameter 
instead (which would allow us to express what you ask for). In what follows,
I copy the relevant parts of the corresponding email discussions.

Olaf Hartig wrote [1]:
> Graham wrote:
> > Olaf Hartig wrote:
> > > [...]
> > > *) Regarding the first Issue (i.e. a separate Link header field for
> > > anchor or anchor as a parameter): We should pick the second because it
> > > is precise about which provenance-URI is associated with which
> > > context-URI.
> >
> > That is true.  But that [precision cannot be achieved using the
> > alternative mechanisms. especially HTML <link> element, so I'm actually
> > leaning the other way.
> 
> I would consider HTTP Link header fields more important than HTML link
> elements  because they serve a more general use case. In other words, we
> shouldn't introduce an unnecessary limitation in the preciseness of the
> HTTP Link based mechanism that we propose, only because the (more
> specific) HTML link based mechanism isn't expressive enough.


Graham Klyne wrote [2]:
> Yogesh Simmhan wrote:
> > [...]
> > Graham:
> > | Yogesh:
> > | > [...]
> > | > *) "An HTTP response may include multiple provenance link headers...
> > | > Likewise, an HTTP response may include... "
> > | > - Besides the above issue of the provenance being related to the
> > | > resource being accessed (rather than the context-uri), I would like 
> > | > some clarity on what the multiple "anchor" mean. I would expect when 
> > | > multiple provenance-URIs and context-URIs are returned through 
> > | > multiple "Link:" headers, then one or all the provenance-URIs *may* 
> > | > describe one or all the context-URIs. It is upto the accessor to 
> > | > access each of the provenance-URIs to determine which of them describe
> > | > which context-URIs. If this is indeed the intention, can it be made
> > | > clearer? Also, it is not clear what resource you mean by "the resource
> > | > may": the provenance resource or the resource being accessed by the 
> > | > HTTP GET/HEAD?
> > | 
> > | Yes, this is a point that needs clarifying.  It is also a (small)
> > | difference between using "Link anchor=..." vs two separate link
> > | headers.
> > 
> > Yes, that is true.
> 
>  From thinking about Olaf's comments, I'm starting to think the "anchor"
> and provenance context-URI might be subtly different.  Still thinking.


Cheers,
Olaf

[1] http://lists.w3.org/Archives/Public/public-prov-wg/2011Aug/0256.html
[2] http://lists.w3.org/Archives/Public/public-prov-wg/2011Aug/0253.html

Received on Tuesday, 23 August 2011 06:25:02 UTC