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After this interesting conversation with Neno, let me start

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the lesson by defining what a software architecture is.

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And to do that, I'm going to use two

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seminal definitions. The first one is from Dewayne Perry

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and Alex Wolf. And they define a software architecture

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as elements, form and rationale. In this definition, the

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elements are the what, which means the processes, data,

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and connectors that compose a software architecture. The form

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is the how, the set of properties of

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in relationships among these elements. And, finally, the rationale

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is the why, the justification for the elements and

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their relationships. The second definition I want to use

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is from Mary Shaw and David Garland. And

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they defined a software architecture as a level of

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design that involves four main things, a description of

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elements from which these systems are built, the interactions

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among those elements, the patterns that guide their composition, and

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finally, the constraints on these patterns. As you can see, these

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definitions are fairly similar and there are many more alternative

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definitions of software architecture. In fact, if we try to search

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the term software architecture, we get over two million entries.

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And if we look at the images in the results of

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the search this is what we get. And I like this

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sort of graphical depiction because it gives you a clear idea

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the software architecture are prevalent concept, given the number of

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results. But they also show you clearly, that software architecture are

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complex entities, if you look at some of these pictures.

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And ultimately, they show that software architecture are presented in all

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kinds of ways including in 3D, if you look at this

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picture. We cannot clearly cover all of these definitions in one

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lesson. So what I will do instead, is to introduce

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a very general definition that encompasses most of the existing ones.