> > > <distance>100</distance>
> >
> > > means "distance from center of town."  Accordingly, the client's 
> > > application does calculations based on that meaning.
> >
> > > In the version 2 data the... semantics of the <distance> element is 
> > > changed to "distance from town line."
> >
> 
> actually I really hated that example because I found it 
> somewhat unrealistic for something that would actually 
> happen, and somewhat data-apocalyptic.

Actually, I really liked it because it's the kind of thing that happens all
the time. Or more likely, in version 1 there's no clear definition of what
<distance> means, and different parts of the user community start
interpreting it in different ways; then version 2 clarifies the meaning, and
some parts of the user community find that their previous interpretation is
no longer valid.

Have you never experienced a change in procedures for expense claims where
version 1 allowed you to claim for travel between two company sites based on
the shortest route, and version 2 allowed you to claim based on the mileage
of the fastest route, but the data sheets giving the distances between
company locations weren't actually updated? If you think that's apocalyptic,
you've worked in very well organised companies.

Michael Kay
http://www.saxonica.com/