Re: [xsl] Kleene Operators

Subject: Re: [xsl] Kleene Operators
From: "G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>
Date: Sun, 28 Feb 2010 14:58:58 -0500
At 2010-02-28 11:48 -0800, Terry Badger wrote:
I have been using Michael Kay's XSLT book and see that the regex, XSL and DTD occurrence operators are defined in set theory. I wonder how important this is when we use them. I guess my question is: does something very useful happen as the result of using these operators in XML activities that would not have happened had we used something else?

When I teach XSLT and XQuery set theory comes into play a lot, of course mostly when talking about the XPathy operators union, intersect and except. I find the use of "union" is extensive, the use of "except" common and the use of "intersect" rare in my work. In the class exercises I expect students to make use of "union" and "except".

Kleene operators are familiar to the programmers who attend the class. Cardinality is well known to database people.

I'm not sure where your question is coming from regarding "importance" ... aren't all of these concepts critically important to working with information of any kind? If we weren't using the already-familiar notation of Kleene operators, wouldn't something else be more confusing?

This was a lesson I learned almost two decades ago when I was on the project team developing the Near and Far graphical DTD editing tool: being a graphical interface we implemented icons for each of the Kleene operators and found ourselves having to teach users something new for what they already understood. It was a drawback to use something other than what was already in use.

I'm curious what compelled you to ask the question ... can you think of a better way to express these concepts and you think the industry made a mistake leveraging what is already there? I don't mean that question in a negative sense as it may sound ... I'm really trying to understand what triggered the question.

I hope this helps.

. . . . . . . . . . . . . Ken

-- XSLT/XQuery training: after 2010-03-15/19 XSLT/XQuery training: San Carlos, California 2010-04-26/30 Principles of XSLT for XQuery Writers: San Francisco,CA 2010-05-03 XSLT/XQuery training: Ottawa, Canada 2010-05-10/14 XSLT/XQuery/UBL/Code List training: Trondheim,Norway 2010-06-02/11 Vote for your XML training: Crane Softwrights Ltd. G. Ken Holman mailto:gkholman@xxxxxxxxxxxxxxxxxxxx Male Cancer Awareness Nov'07 Legal business disclaimers:

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