Re: Spec text for Unified_evaluation_context (Action 2008-01-23.1)

Hi Nick,

I thought we had discussed a syntax that was better than the original 
proposal, namely that each possible MIP could possibly be expressed by a 
child element of the same name, whereupon the context attribute could be 
used on that element.  Like this:

<bind nodeset="c">
    <calculate context=".." value="a + b"/>
</bind>

This has several benefits.

First, it is easier to say that the *bind* identifies the nodes to which 
MIPs are applied, whereas the <calculate> element is only concerned with 
providing a more sophisticated way of expressing the formula.  There is no 
confusion about what node the formula applies to because the context 
attribute is not being placed on an inner bind.  In other words, it is 
easier to say that context on the calculate element only overrides the 
evaluation context of the value attribute and does not interfere in any 
way with the node to which the result of the formula is applied.

Second, it allows us to simplify the expression of boolean results.  For 
example, must we really call boolean-from-string() on expressions whose 
result is known to be boolean?  Specifically, the element relevant could 
be defined as automatically applying boolean-from-string to the string 
result of the value attribute in the following:

<bind nodeset="node/a">
    <relevant context=".." value="b"/>
</bind>

It's up to the group to decide if they want this extra semantic for 
relevant, readonly and constraint, but lots of people consistently forget 
to put boolean-from-string() until they get burnt by it.  Even if we used 
'boolean' rather than 'value', it would be better, e.g.

<bind nodeset="node/a">
    <relevant context=".." boolean="b"/>
    <readonly context=".." boolean="c"/>
</bind>

Third, using MIP named child elements allows the possibility for 
combinators on some of the MIP types, especially constraint, e.g. the 
following would say that node a is invalid unless (b and c and (d or e) 
and (not f)):

<bind nodeset="node/a">
    <constraint context=".." operator="and">
          <constraint boolean="b"/>
          <constraint boolean="c"/>
          <constraint operator="or">
                 <constraint boolean="d"/>
                 <constraint boolean="e"/>
         </constraint>
          <constraint operator="not" boolean="f"/>
    </constraint>
</bind>

Cheers,
John M. Boyer, Ph.D.
Senior Technical Staff Member
Lotus Forms Architect and Researcher
Chair, W3C Forms Working Group
Workplace, Portal and Collaboration Software
IBM Victoria Software Lab
E-Mail: boyerj@ca.ibm.com 

Blog: http://www.ibm.com/developerworks/blogs/page/JohnBoyer
Blog RSS feed: 
http://www.ibm.com/developerworks/blogs/rss/JohnBoyer?flavor=rssdw





Nick_Van_den_Bleeken@inventivegroup.com 
Sent by: public-forms-request@w3.org
02/01/2008 06:20 AM

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Subject
Spec text for Unified_evaluation_context (Action 2008-01-23.1)







All, 

Attached to this e-mail you can find a draft  HTML and spec-xml version of 
the work I did for 
http://www.w3.org/MarkUp/Forms/wiki/Unified_evaluation_context. 

In short I added the context attribute to bind and added an example of how 
this enables you to 'simplify' your XPath expressions on MIPs. 

Please have a look at it, 

Nick Van den Bleeken 

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