Mike, Wendell

Thanks for your help on this subject. I've written my replies below:

Mike Wrote:
Date: Tue, 31 Jul 2007 18:08:26 +0100
To: <xsl-list@xxxxxxxxxxxxxxxxxxxxxx>
From: "Michael Kay" <mike@xxxxxxxxxxxx>
Subject: RE: [xsl] Stepping through XPath in a visual XPath debugger
Message-ID: <014201c7d395$69196bd0$6401a8c0@turtle>

>>
>> a) What is the most intuitive order in which to step-through
>> an XPath 1.0 expression visually?

>I really don't know the answer to this, but I think anything that presents a
>view of the evaluation as a sequential process is misleading and likely to
>be unhelpful. The concept should be to select parts of the expression and
>understand what contribution they make to the result - for example, being
>able to see which nodes a particular predicate is applied to, and which of
>them match.

>Michael Kay
>http://www.saxonica.com/

Mike: I understand your concern about presenting XPath evaluation as a
sequential process. I will look again at the user interface for my
application in an attempt to ensure that it does not create such a
false-impression. There is already support for selected parts of the
expression to be highlighted and their contribution to the result shown,
but this should probably be emphasised somehow.

Perhaps a resonable parallel here could be found in Regular Expression
tools, so I will look to these for some ideas. Some consistency might
also be useful in future, given XPath 2.0's support for Regular Expressions.
-----------------------------------------

Wendell Wrote:
Date: Tue, 31 Jul 2007 15:33:23 -0400
To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Subject: RE: [xsl] Stepping through XPath in a visual XPath debugger
Message-ID:<20070731153834.GA59777@xxxxxxxxxxxxxxxxxxxxx>

>While admitting, in sympathy with this caution, that it is an
>academic exercise to view the evaluation of an XPath expression
>sequentially, it might be helpful to see how we've learned to teach
>neophytes to interpret XPath 1.0 location paths:
>...

Wendell:  A useful insight into the world of XSLT training.
Its interesting that you have reservations on introducing abbreviated
XPath to students too early.

The problem faced by this tool (as with many) is that it has to meet the
conflicting needs of a number of different types of user. From beginners
to experts and from occasional users to freqeunt users. It may be that
I should introduce a special mode that could avoid the use of XPath
abbreviations in debugging and in auto-generation. The auto-complete
feature could also be bolstered to ensure full support for the
non-abbreviated form.

Wendell's last paragraph:
>...
>Note that there have already been some worthy visualization tools for
>XPath, but nothing is a substitute for a concrete, meaningful
>example. While being able to visualize it generally is useful, it
>really clicks into place when students can see *why* particular
>XPaths are used in particular situations. This helps to dramatize
>which sorts of things matter (context nodes) and which ones don't
>(short or long syntax).

I agree with your observation that there are already a number of worthy
XPath visualisation tools, and I would be the first to recommend their
use. Hopefully I'm doing no harm here in aiming to provide another
example and exploring some of the boundaries.

You mention that, in training, there is no real substitute
for concrete examples. Do you know a good non-copyright resource for
such examples - preferably in xml form? One of the features of this
application is to allow the development and management of large (xml)
libraries of XPath expressions. The import feature (using a 'special'
XPath library) could make use of such a resource. Initially this would
be helpful for testing but these could also be included with the product
if and when this gets past 'Beta'state.

Thanks

Phil Fearon
http://www.sketchpath.com/