A sumproduct() function proposed for XForms 1.2

Hello all,

One of the small features I proposed for XForms 1.2 is a function called 
sumproduct() which takes the sum of the pairwise products of two nodesets.

Nick responded that this function seemed a little odd because it was 
essentially calculating two results.  However, it is really only 
calculating and returning one result.  Moreover, that result can be 
determined using a single pass through the two nodesets provided. 

A quick web search for "sumproduct" will indeed show that this is a 
*standard* spreadsheet function.  The main point is that on spreadsheets, 
they actually allow more than two arrays.  The function accumulates the 
sum of the products of the corresponding elements in each of the arrays 
provided.

I believe it is likely that this function will be needed for our no-model 
XForms development, and I am certain it is useful in forms today.  Here is 
an example:

<group ref="/purchaseOrder/items">
  <repeat nodeset="item">
    <input ref="productName"> ...
    <input ref="quantity">...
    <input ref="price">...
    <output value="price * quantity">
       <label>Product Value</label>
    </output>
  </repeat>

  <output value="sumproduct(item/quantity, item/price)">
      <label>Subtotal</label>
  </output>
</group>

You can see here that instance data was not needed for the row products in 
order to calculate the subtotal over the whole table.

This is good because we don't want limitations of XForms to force people 
to write their data schemas differently.  A key message we have for XForms 
is that we provide interactivity and fill experiences for instances of 
schema defined by the data architect. 

For no-model XForms development, I think that the output control may not 
result necessarily in a data node in the implicit instance.  In this case, 
there would not be a row product value to refer to, which is analogous to 
the situation I created above by using a value attribute on the output in 
the repeat.

Now that there has been some discussion on this, it makes sense to make a 
thread for it to
A) find out if there are any other objections to adding this function
B) to see if I've managed to convince Nick yet :-)

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