Location Property

The current draft EARL schema does not seem to have any properties to 
describe the location of the error. We've discussed these issues earlier on 
the list [1] and I believe we need these properties and that they should be 
part of the assertion. Here's my formal proposal:

1) Each assertion that describes an error needs to describe where the error 
occurs. For example, if an HTML page contained the error "image is missing 
an alt attribute" we need to state which image. It's not enough to simply 
state that the content contains an error, you've got to state where it is.

2) The location properties that we use to describe the error is dependant on 
the accessibility test that is performed. For example, the properties used 
to describe HTML errors will be different from the properties used to 
describe errors in Flash or PDF.

3) The location properties should be precise and interoperable. We need to 
describe as clearly as possible where the error occurred and this should be 
done in a standard manner so the results may be exchanged with other 
programs. I suggest that for HTML errors we require that at least one xpath 
expression be used to describe the accessibility error.

4) More than one location property may be required. For example, to describe 
a series of links that should be grouped with a list element, properties to 
identify all the links in the group would be required. The number of 
location properties is dependant on the accessibility test. If more than one 
location property is used then each property must have a title to describe 
itself.

5) Other optional location properties may be included. For example line and 
column numbers could be included as well as xpath expressions.

6) The location properties apply to the content evaluated and do not 
necessarily locate the error when the document has been modified.

7) Other location 'hint' properties may be included for finding the error if 
the document is modified.

Example EARL code for discussion:

This example locates an image within the document that has failed the test 
"all images must have an alt attribute".

<earl:Location>
<rdf:Bag>
<rdf:li rdf:parseType="Resource">
<dc:title>key-element</dc:title>
<earl:xpath>/html/body/p/img[@src="rex.jpg"]</earl:xpath>
<earl:column>24</earl:column>
<earl:line>9</earl:line>
</rdf:li>
</rdf:Bag>
</earl:Location>

This example locates the anchor that has failed the test "all source anchors 
contain text that describes the link destination". Here is the problem HTML 
code:
<a href="spending.html"><img src="more.gif" width="30" height="10" 
alt="image"/></a>

The problem is that the alt text for the image does not describe the link 
destination.

<earl:Location>
<rdf:Bag>

<!-- the anchor element -->
<rdf:li rdf:parseType="Resource">
<dc:title>key-element</dc:title>
<earl:xpath>/html/body/p/a[@href="spending.html"]</earl:xpath>
<earl:column>109</earl:column>
<earl:line>9</earl:line>
</rdf:li>

<!-- the image within the anchor -->
<rdf:li rdf:parseType="Resource">
<dc:title>link-text-image</dc:title>
<earl:column>165</earl:column>
<earl:xpath>/html/body/p/a/img[@src="more.gif" and 
@alt="image"]</earl:xpath>
<earl:line>9</earl:line>
</rdf:li>

</rdf:Bag>
</earl:Location>

Comments appreciated.

Cheers,
Chris

[1] http://lists.w3.org/Archives/Public/public-wai-ert/2005Mar/0092.html

Received on Monday, 18 July 2005 14:33:06 UTC