RE: [xml-dev] The Airplane Example (was Re: [xml-dev] StreamingXML)

["Kirkham, Pete (UK)" <pete.kirkham@baesystems.com>]

(These are entirely mine own opinions, not those of my employer and I am not in any way a spokesman for BAE Systems)

Michael Kay [mailto:mike@saxonica.com]
> I came across a stylesheet recently with a bug: it was designed to display
> out-of-range data in red, and this wasn't happening, because the code was
> doing a string comparison rather than a numeric comparison. I can think of
> many scenarios where this could have fatal consequences: admittedly they all
> have a human in the loop, but that's not guaranteed to prevent the disaster
> happening.

If there's a human in the loop then that human may be red-green colour blind, so this particular case should never be safety critical, unless you have very rigourous operator screening.

hhalpin@ibiblio.org [mailto:hhalpin@ibiblio.org]
> Still, if someone was going to use XML in some capacity to shoot missles
> or aid in flying airplanes (which, given the increasing variety of things
> XML is used for, could happen soon!), an XML-aware language with static
> typing and proof-proving capabilities would be one way to go.

More bytes of data are processed in the production of the safety case and AWFL (air worthiness flight limitations, pron. awful) documents than in the on-board systems of Typhoon (The aircraft formerly known as Eurofighter).

Currently these documents are processed via MS Word 97 on Windows NT. In the next few months we shall be upgrading to Word 2003 on XP, and XML will be part of the process. I've already been prototyping an SVG app for the Mach/height/incidence plots which show where you can fly with various stores configurations.

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.


Pete

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