Hardware fails randomly: it's meaningful to talk about the probability of
failure.
Sofware fails predictably. With very rare exceptions, a program either works
correctly every time, or it never works at all. Probability of failure is
therefore a meaningless concept. (The main exceptions are (a) multithreading
effects, and (b) when the program is supplied with abnormal input.)
Of course, all software has bugs, and that includes XSLT/XPath processors. Bugs
in a compiler don't usually have a serious effect on safety-critical systems
because nearly all compiler bugs are found while developing and testing the
user application; they don't suddenly spring into life in the middle of the
night when the patient is on the operating theatre.
(I remember a three-day trial of a mainframe operating system prior to release.
The success criterion was that it achieved a mean time between failures above
24 hours. In the event there were 3 failures over 72 hours. They were all
caused by the operator loading a particular deck of cards upside down. After
three crashes he realised his mistake, and didn't do it again. What was the
probability of that happening?)
Michael Kay
Saxonica
On 15 Nov 2019, at 12:09, Costello, Roger L. costello(_at_)mitre(_dot_)org
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> 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?
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? 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)?
/Roger
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