Re: Interresting thread in comp.lang.eiffel

[David Gillon <david.gillon@baesystems.com>]

David K Allen wrote:

> Applying business principles to the software engineering "Design By
> Contract" will not really help much.
> Conversely, trying to apply Dr. Meyer's software engineering principles to
> the socio-political issues will not help either.
> They are two different domains with different principles and techniques.

Unfortunately, for the type of project we're discussing here the two
uses of contract (requirements and legal) are likely inseperable, so
Ken's arguments are a criticism based on real-world experience of the
argument that DBC would have automatically solved the coordination
issues (which is where we started). In an ideal world (where software
engineers write the rules), maybe, in the real world, with lawyers,
accountants and non-technical managers to be worked around the issue is
much less clear.

> But the point is that if DBC were a component of the software development
> method used to build Ariane, then any attempts to reuse software from a
> previous project would force the issue that the new project teams MUST HAVE
> the specifications of any modules they intend to reuse.   If that had been
> part of the software develoment culture, then the subcontractor would have
> required the additional information and the contractor would have gladly
> complied and provided it.

But the contracts between the companies were at the 'you provide a black
box to meet this requirement' level, far above the level at which
'software development cultures' function. The need for information
exchange for DBC would first have had to be pursued up multiple levels
of the sub-contractor management tree until a level was reached at which
the release of information could be sought, and then on the contractor
side chased back down the tree until someone was found who could explain
what was wanted. Think Dilbert 1 trying to have a technical discussion
with Dilbert 2 by passing verbal messages through ten layers of pointy
haired bosses each.... The assumption that this would logically result
in the contractor 'gladly complying' doesn't necessarily reflect what
happens in reality. And this is without even considering the security
and clearance issues many such projects have to deal with.

One thing I'm still waiting to hear in this discussion is how Eiffel
would handle a temporal constraint of the type 'Signal A will be updated
with its new value within 2.5 ms of a change to any of its source
inputs'.

-- 

David Gillon