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Re: Compound Locations

From: Shadi Abou-Zahra <shadi@w3.org>
Date: Mon, 26 Sep 2005 11:07:17 +0200
Message-ID: <4337BA45.4000007@w3.org>
To: Charles McCathieNevile <chaals@opera.com>
Cc: Nick Kew <nick@webthing.com>, public-wai-ert@w3.org


Charles McCathieNevile wrote:
>> There are a couple of simple cases we can perhaps express:
>> * Range (Start-point + End-point)
>> * Main+subsidiary locations
>> But I think anything more complex has to be tool-specific.
> ...
> Actually, except for maybe a couple of specific cases such as ranges  
> (which are actually defined in, for example, one of the  
> Xpath/pointer/thingo constellation of specs, IIRC) and perhaps a 
> "happens  here, should be here too" or something for stuff like missing 
> closing  tags, I think we should be saying that the list of things has 
> no  meaningful structure.

Tangent: I think we can not rely on XPath/XPointer/XQuery features now, they only work on some documents.

Are you suggesting having three "types" of cases:

* Range
* Main+related/subsidiary/etc
* Unstructured

> I favour using collection in some cases - i.e. this is the complete 
> list,  but we should note that the order is not significant. I am not 
> sure how  easy this is to do, since in theory a parseType="Collection" 
> list is  completely ordered, and it is painful (but not impossible) to 
> construct a  query that tests only whether it contains the same items.
> In other cases we may have a reason to use an open-ended collection like 
> a  Bag.

As you note, RDF containers (Bag, Seq, Alt) and collections are quite difficult to query (for example to compare if two assertions are talking about the same location). IMHO, it is better to use explicit properties to express the relationships (for example "hasPart" type of relations). This does bloat the code of the schema and instances but simplifies queries a whole lot.

> By the way, the same structural issue comes up for evidence - that we  
> should not imply more meaning to a list of items than where we can 
> develop  interoperable algorithms and a proof of necessity.

Agree, similar issues. We should discuss if we want to continue using the collection approach or rather propose properties with range earl:Evidence and domain earl:Assertion.


Shadi Abou-Zahra,     Web Accessibility Specialist for Europe 
Chair and Team Contact for the Evaluation and Repair Tools WG 
World Wide Web Consortium (W3C),           http://www.w3.org/ 
Web Accessibility Initiative (WAI),    http://www.w3.org/WAI/ 
WAI-TIES Project,                 http://www.w3.org/WAI/TIES/ 
Evaluation and Repair Tools WG,     http://www.w3.org/WAI/ER/ 
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Received on Monday, 26 September 2005 09:07:26 UTC

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