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Re: Pointers model

From: Shadi Abou-Zahra <shadi@w3.org>
Date: Wed, 19 Sep 2007 12:00:03 +0200
Message-ID: <46F0F323.90101@w3.org>
To: public-wai-ert@w3.org

Hi,

Carlos Iglesias wrote:
> 
> Here's a new approach to the overall Pointers Model based on the previous model [1], the discussions about it (see thread starting at [1]), and the proposal from Shadi [2].
> 
> Pointer (ptr:pointer)
> |-PointerGroup 
> | |-RelatedPointers
> | '-EquivalentPointers
> |-SinglePointer (ptr:reference)
> | |-ExpressionPointer (dc:hasVersion, ptr:expression)
> | | |-XPathPointer (ptr:namespace)
> | | |-XPointerPointer (ptr:namespace?)
> | | |-CSSPointer
> | | '-[HTMLPointer]
> | |-OffsetPointer (ptr:offset)
> | | |-CharOffsetPointer
> | | '-ByteOffsetPointer
> | |-SnippetPointer (ptr:snippet)
> | | |-CharSnippetPointer
> | | '-ByteSnippetPointer
> | '-LineCharPointer (ptr:line, ptr:char)
> '-CompoundPointer (ptr:startPointer)
>    |-StartEndPointer (ptr:endPointer)
>    |-StartOffsetPointer (ptr:offset)
>    | |-StartCharOffsetPointer
>    | '-StartByteOffsetPointer
>    |-StartSnippetPointer (ptr:snippet)
>      |-StartCharSnippetPointer
>      '-StartByteSnippetPointer
> 
> The differences with Shadi's proposal are basically:
> 
> - Everything is a Pointer (PointerGroups included). I think that, regardless of our needs within the group, if we want people reusing the pointers this is the best approach (we shouldn't force people to use PointerGroups every time they want to use a Pointer). Additionally I don't see any benefit in separating PointerGroups from the rest of Pointers.

OK, I can agree to that.


> - It uses StartCharOffsetPointer and StartByteOffsetPointer instead a generic StartOffsetPointer that makes use of the Single OffsetPointers to avoid the duplication of ptr:reference (startPointer and OffsetPointer) that may give way to inconsistence if they are different (a CompoundPointer should exist only within a unique resource).
> 
> - The same as above with StartSnippetPointers

This solution is far from optimal in my opinion. What if I want to 
introduce a new XYZOffsetPointer? Since it is easy to do a query like 
("offsetNode" rdf:type ?) and find out what kind of a pointer type it 
is, I don't think it is a good idea to be that restrictive.


> That leads us yet to one issue: we have yet a duplication of ptr:reference that could lead to inconsistence in StartEndPointers as startPointer and endPointer are both SinglePointers. We have a similar problem with EquivalentPointers
> 
> Any thoughts?

Maybe this makes sense. For example, consider this:

StartPointer:
  - reference: http://www.example.org/page.html#section1
  - (XPath) expression: relative to the ID "section 1"
EndPointer:
  - reference: http://www.example.org/page.html#section3
  - (XPath) expression: relative to the ID "section 2"


Similar situations could be constructed for EquivalentPointers, 
especially if there are GET parameters in the reference URI. I think 
this model is fine with regards to the reference.


> [1] - [http://lists.w3.org/Archives/Public/public-wai-ert/2007Jul/0042.html]
> [2] - [http://lists.w3.org/Archives/Public/public-wai-ert/2007Jul/0049.html]


Regards,
   Shadi


-- 
Shadi Abou-Zahra     Web Accessibility Specialist for Europe |
Chair & Staff Contact for the Evaluation and Repair Tools WG |
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Received on Wednesday, 19 September 2007 10:00:12 GMT

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