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On Tue, 2005-01-04 at 16:41 +0000, Kirkham, Pete (UK) wrote:
> All these documents require inspection by multiple human experts prior to issue, and are text or graphics rather than data, so type systems do not figure.
>
> Since there are occasional semantic errors (m may be miles or metres- the authority rings up the author and it is expanded, currently the different AWFLs for different planes need compiling by hand rather than automatically via a query off a database) I've thought about using a controlled English that is machine parsable (rather than presenting the users with XML or RDF), but the gain for such a system is not likely to exceed the cost- most of the checks worth anything are in the heads of the grey-haired engineers, not any type system. I've had a lot of experience with trying to get Z, graph based argumentation and Goal Structuring Notations into such systems for safety case management, but without much success. Basically the people who are experts in safety don't trust automation when there's an extant reliable alternative.
Exactly. Real life error conditions almost never fall along the neat
lines that strongly, statically typed language designers draw. I don't
think I can recall having *ever* had a program fail because someone
passed a float to a routine that expected an int. Most errors by most
competent programmers (IMO) are of much sterner stuff. And the problems
with most strongly, statically typed languages is that their strong
typing decreases expressiveness of axioms to the extent that it's not
even easy to arrange to catch the real sorts of errors that can occur
(although, luckily the recently revived test-first philosophy is helping
a lot with that).
I have never believed the notion that strong static typing increases
safety, and that's for general-purpose languages. In the case of XML
applications, I go further to consider such ideas of type safety fairly
ludicrous.
--
Uche Ogbuji Fourthought, Inc.
http://uche.ogbuji.net http://4Suite.org http://fourthought.com
Use CSS to display XML - http://www.ibm.com/developerworks/edu/x-dw-x-xmlcss-i.html
Full XML Indexes with Gnosis - http://www.xml.com/pub/a/2004/12/08/py-xml.html
Be humble, not imperial (in design) - http://www.adtmag.com/article.asp?id=10286
UBL 1.0 - http://www-106.ibm.com/developerworks/xml/library/x-think28.html
Use Universal Feed Parser to tame RSS - http://www.ibm.com/developerworks/xml/library/x-tipufp.html
Default and error handling in XSLT lookup tables - http://www.ibm.com/developerworks/xml/library/x-tiplook.html
A survey of XML standards - http://www-106.ibm.com/developerworks/xml/library/x-stand4/
The State of Python-XML in 2004 - http://www.xml.com/pub/a/2004/10/13/py-xml.html
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