Re: Ada in command / control systems

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 19-03-05 11:51 , Maciej Sobczak wrote:
   ...
> Everybody relies on pictures and the general consensus is that you
> cannot do proper engineering without them. So there is nothing
> strange if people expect pictures in software engineering, too.

Anecdote regarding the importance of pictures:

A colleague of mine was working on some on-board satellite SW 
(ultimately) for ESA. At the SW Requirements Review, the customer's 
representative (that is, the main reviewer) rejected the SW Requirements 
Specification (the object of the review) as "poor" and demanded that it 
be "rewritten" -- a very unusual level of criticism.

After some close questioning the reviewer admitted that he had only 
glanced at the document and decided to reject it because it contained no 
pictures or diagrams. He had not read enough to have found any specific 
errors or shortcomings.

Fortunately, the other reviewers had a better opinion of the document 
(having actually read it) and the review passed with only the usual 
amount of corrections required. End of anecdote.

I'm not sure which side -- if either -- of the present argument this 
anecdote supports, but I tend to agree with Dmitry on the limitations of 
the graphically oriented model-based-design tools. When the model and 
design are devised and shown at so high a level as to be easily 
comprehensible, the model usually becomes approximate, which means that 
running code cannot be generated from the model.

The design pictures that are really useful for understanding a piece of 
SW are almost always abstractions and simplifications and could be 
called "useful lies". Unfortunately this means that the pictures must be 
manually created, and manually maintained as the SW evolves.

It may be possible to make the model-based design tools encompass more 
levels of abstraction and detail, and perhaps separate aspects of the 
design so that different aspects could be designed and illustrated by 
different diagrams, with the tool able to "weave" all aspects into the 
generated code. The several types of diagrams defined in UML may be an 
attempt in this direction. However, AIUI current model-based tools are 
each based on a single kind of "model" -- say, state-charts -- and then 
Dmitry's criticism applies.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .