Concerned about the increasing reliance on XPath

["Costello, Roger L." <costello@mitre.org>]

Hi Folks,

XPath is a fabulous language. It is incredibly powerful. It is a large, rich language.

I have observed in increasing usage of XPath.

For example, in XML Schema 1.1 the new assert element uses XPath to express constraints:

    <assert test="XPath" />

XPath gives a lot of power to the assert element.

But it also means that a lot of power is needed to evaluate the assert element. 

To evaluate that tiny, innocuous assert element you need to implement the entire XPath language.

Suppose the assert element was simplified. The only kind of assertion that can be made is, "The value of the first child element must be greater than the value of the second child element." Here's how we might use it to express the constraint between a meeting's start time and end time:

<greaterThan>
        <element name="start-time" type="dateTime" />
        <element name="end-time" type="dateTime" />
</greaterThan>

Very little power is needed to evaluate this "assertion".  The assertion is expressed entirely in XML markup.

We've lost an enormous amount of power/expressivity. But we've gained in reduced cost of evaluation/processing/coding. 

While XPath is nice, it is:

    - not XML
    - requires huge amounts of processing (i.e., coding) wherever it's used

I am concerned about the increasing reliance on XPath. 

My Position: In some cases it would be better to ratchet down capabilities and use XML markup rather than XPath.

I know many people will disagree with my position. Let's have a good discussion of the issue. Here's the issue:

Issue: Is the increasing reliance on XPath a positive or negative trend?

(Implicit in this "issue" is an assumption that there is indeed a growing trend toward using XPath)

/Roger