Re: [xsl] Is there an XSLT/XPath processor good enough to use in life-critical applications?

["Liam R. E. Quin liam@xxxxxxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

On Fri, 2019-11-15 at 12:10 +0000, Costello, Roger L.
costello@xxxxxxxxx wrote:
> Hi Folks,
> 
> Are you using XSLT/XPath in a life-critical application such as
> controlling a nuclear power plant or controlling an aircraft flight
> system? 

I'm not...

However, i can say that XML (and EXI) is used in FAA-mandated systems
as well as in more grounded (but not always motionless) scenarios such
as when you stream gasoline into your car's fuel tank (the pump talks
to the computer in the shop with XML, and potentially XML Schema is
used), or when a technicial hooks up their diagnostic system to yur
car's computer - for that matter XML messages are actively wandering
around in many (most?) modern cars all the time.

Trains use XML but of course need fixed buffer heights.

There have even been shoes with XML in them, used to control ipods.

> Can an XSLT/XPath processor be relied on to always return the correct
> results when given a valid XSLT/XPath program and a well-formed XML
> document?

No.

If by valid you mean DTD-valid, there's no way to impose length limits
on CDATA attribute values in a DTD, nor size limits on content. This is
of course because the designers of SGML envisioned the markup and the
text as separate, something that was later the subject of a patent
lawsuit, crazily enough.

However, smoke testing and commercial coverage testing (with Coverity)
has been applied to libxml2 (for example), and security experts
continue to examine the code.

>  Is it possible to quantify or bound the correctness of an XSLT/XPath
> processor? Is there an XSLT/XPath processor that limits the
> probability of getting an incorrect result to 10**(-9)?

You would need a clear definition of bcorrectb to achieve that.
Unfortunately, denotational semantics doesn't connect well with the
fleshly spatial continuum we inhabit, and defining correctness is
currently intractible.

The right question, though, is, surely, does the software do what we
need, sufficiently reliably for our purpose.

And clearly the answer is yes for a great many applications of XML
technologies.

Liam


-- 
Liam Quin, https://www.delightfulcomputing.com/
Available for XML/Document/Information Architecture/XSLT/
XSL/XQuery/Web/Text Processing/A11Y training, work & consulting.
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