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RE: [xml-dev] XPath 2.0 Best Practice Issue: Graceful Degradation

Well, it's really all about contracts, isn't it? If you write a piece of
code, you need to establish a contract with your caller. And the essence of
that contract is whether you validate the data, or the caller validates. If
the caller isn't contracted to validate the data against an agreed schema,
then you're best off validating it yourself. And doing that within the logic
of the XPath expression itself, as you've shown, is not a particularly nice

Michael Kay

> -----Original Message-----
> From: Costello, Roger L. [mailto:costello@mitre.org] 
> Sent: 28 January 2008 19:22
> To: xml-dev@lists.xml.org
> Subject: RE: [xml-dev] XPath 2.0 Best Practice Issue: 
> Graceful Degradation
> Hi Folks,
> Here is a summary of last week's discussion:
> http://www.xfront.com/xpath20/best-practice/graceful-degradati
> on/index.
> html
> Last week David Carlisle raised an excellent point: "it helps 
> to keep [data validity] separate from your program logic."
> In the summary I wrestled with this:
> (a) Keeping data validation and program logic separate, versus
> (b) XPath is shipped around and executed in different, 
> unanticipated environments where it may not be safe to assume 
> that its environment provides schema-validation, and so 
> program logic must address validation.
> I am interested to see what you think: has the summary struck 
> the right balance between validation and program logic?
> /Roger
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