Wednesday, April 16, 2008

Formalism over hacking - contracts, compilers and why engineering matters

At Uni I learnt Ada, in my first job I did Eiffel (and C) and in my second I did Ada (and C) as a result of which a bunch of people sent me a link to this article on how Ada delivered the sort of success that C programmers can only dream about. Udi Dahan then had a post over on InfoQ about how a "traditional" approach failed and required a much more engineering solution and some smart contracts.

Now I'm not going to say that Udi's project would have worked better first time in Ada (it wouldn't) but what it does highlight is something that Ada really helped people to focus on..... what is the range of acceptable results. Udi's project suffered because the expected range of data (tens) and the actual (hundreds of thousands) were so massively different.

The solution that Udi's team came up with appears pretty masterful and a great example of scaling a solution by looking at how the big clumps of data are actually assembled. By looking at the ranges and the manner in which they were created they were able to create a really great engineering solution.

Over on the Ada side the article highlights how Ada really upfronts the cost of development by making people really consider what is possible, what is probable and what shouldn't be allowed. By having these contracts it means that everything is explicit and this produces a greater focus on quality at those early stages of the project.

My experience with Ada was that it not only helped in ensuring this quality but that it really helped in ensuring the quality of the average developers on the team. Bluntly point an average developer in Ada was a productive member of the project, an average developer in C was a complete liability.

With all the talk of dynamic languages, scripting and late validation it is worth considering that when it really has to work it is always best to take an engineering approach and look at the contracts and ranges of information and to restrict the system to the correct handling of ranges rather than assuming that the system will be able to correctly handle everything.

As SOA becomes a standard way of operation and the issues of networked computing increase a focus on quality and contracts will become ever more important.

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Udi said...

Glad you liked the article. The story is actually made up, but it serves as a great instructional aide (not to mention that it makes it easier to write too ^_^ ).

Greg said...

Made up? Thats good (although that changes the story from experience report to fairytale), I would hate to think that someone so experienced could have so monumentally screwed up the obvious bits of their performance analysis...