Why is software engineering not engineering?

As I had a look over Philippe Kruchten's book "The Rational Unified Process. An Introduction" I noticed the following passage. I mean, the book is rather dry, it just describes some organizational process, but this paragraph was different:

"Software engineering has not reached the level of other engineering discipline .... because the underlying "theories" are week and poorly understood and the heuristics are crude."

Well, nothing new here, just like we all know it to be. Then:

"Software engineering may be misnamed. At various times it more closely resembles a branch of psychology, philosophy or art than engineering. Relatively straightforward laws of physics underlie the design of a bridge, but there's no strict equivalent in software design. Software is "soft" in this respect."

Indeed! In programming we are not working with physical materials but with mental objects (or should I say artifacts?) denoted by an array of characters on a sheet of paper. Sometimes even with just boxes and lines*. So what we really are doing, when we're trying to set up some laws in software, is looking for the "laws of thought", i.e. we are trying to find a good way to organize our ideas! Ideas which will then become flesh when executed on a complicated machine. As we are working with mental objects to a much greater extend than traditional engineering, the methodology cannot be the same. The world of human thought is not so well explored as the physical world. Or maybe the physical world is just much, much simpler?

This discussion would lead us too far**, but one thing is sure: on some level of abstraction, we are no more thinking about the underlying machine, a thing which couldn't happen when we were designing a bridge. Because of that I maintain that in programming we are basicaly working with mental and not physical objects, so it cannot be counted as engineering. That might be the case earlier on, as programmers had all the iron on their hands, setting plugs and connecting cables. It had an engineering-like looks. But today? Just look on an corporate IT department - it's all about organisation, processes, abstractions of every level. For me it has more to do with "management science" and even "social science", only on a different scale.

So it should be best called computer "science" - not in the "scientific" sense, but rather in the "soft-science" sense? This would however mean, that it is somehow an art... Well, it's not what the industry wants to hear! But we don't have to tell them ;-).

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* MDD (or should I call it MDA?) takes it to the extreme: you don't write ANY code at all, instead you are writing the "computation independent model", of course in UML, which constitutes a description of the functionality of the system. Then you are transforming this model into another model: "platform independent model", which represents the abstract computation model, then you are tranforming this into a "platform specific model" at last. And all of this is done using tools, profiles, configurations, cartriges. Ideally, you should only model the required functionality, choose the target platform, and start the model transformation chain. Cool! But is it still programming? Theoreticall it is.

** i.e. into philosophy. Just consider that civil engineers are working with mental models too, and, on the other side, the matematicians are working with "mental objects", which miraculously can describe the physical worlds with a great precision...