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LC: Issues with repeat index manipulation and generalized insert/delete actions

From: John Boyer <boyerj@ca.ibm.com>
Date: Thu, 12 Apr 2007 16:01:26 -0700
To: www-forms-editor@w3.org
Message-ID: <OFE517B52A.2F486B01-ON882572BB.007AB301-882572BB.007E7AB8@ca.ibm.com>
Three issues regarding Section 9.3.5 and 9.3.6 (and technically 9.3.1):

1) When insert or delete actions occur, the repeat index is updated for 
any repeat bound to node(s) inserted or deleted.

Currently, this is described in the insert and delete actions, which is 
inappropriate since it is a property of repeats.  The intent of insert and 
delete in XForms 1.1 is to be generalized data manipulators, so they 
should not contain language about manipulating repeat indices.

Moreover, now that we have the proper context information in xforms-insert 
and xforms-delete it is even possible to describe how repeat index 
manipulation could be achieved by having repeat semantics imply listeners 
for xforms-insert and xforms-delete with index update according to whether 
the nodes listed are applicable to the given repeat.

Although this is an implementation, I think it is important to preserve 
the property that the repeat indices are updated immediately (as is the 
case now) and not at some later time that might seem more obvious, such as 

2) It is completely unacceptable to me that the index of a nested repeat 
is reset when its containing repeat's index is updated.  This behavior 
should simply be stricken from XForms 1.1 as there is no earthly reason 
for doing it. 

I believe it was added to XForms 1.0 at a time when repeating was not 
nearly as well understood as it is now.  I believe there was the thought 
that there would only exist one instance of a data structure to represent 
any repeat, including an inner repeat,  Hence the index of that object 
would be changed to the start value in a newly inserted repeat item 
(9.3.5, bullet 8).  I believe similar reasoning was used to arrive at 
inner repeat reinitialization in the delete case (9.3.6 bullet 5).

However, we now know that inner repeats are similar to inner switches in 
an outer repeat.  Just as the selected case of a switch may be different 
in each repeat item, the index of an inner repeat may be different in each 
repeat item.  Hence there is no need to modify the indexes of inner 
repeats when a repeat item in the outer repeat is created or destroyed, 
just as there is no need to reset the cases of all switches in all repeat 
items just because one is added or deleted. 

Alternately, observe that if the inner repeat index adjustment really were 
necessary on insert and delete, then there would be a flaw in that case 
adjustment of repeated switches would also be needed, and the spec makes 
no allowance for this.

The proposed solution is that XForms should retain only the simpler 
behavior which says that a repeat index is updated if the context node of 
the indexed repeat item is deleted or if a new node is inserted into the 

3) Insert and Delete are now in the wrong section.

In XForms 1.1, insert and delete have become generalized data 
manipulators.  They are not really tied to repeat anymore in that we do 
suggest their use in other cases, like extracting the data payload from a 
SOAP envelope.  To avoid confusion that insert/delete should only be used 
with repeated data, they should be moved to Section 10.

This of course is another good argument for moving the index updating 
logic to repeat in 9.3.1.

John M. Boyer, Ph.D.
STSM: 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
Received on Thursday, 12 April 2007 23:01:41 UTC

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