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We can look at the software architecture from two

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main standpoints. There are prescriptive and descriptive software architectures.

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So what does that mean? A prescriptive architecture captures

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the design decisions that are made prior to the

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system's construction. This is what we normally call the

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as-conceived software architecture. Conversely,

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a descriptive architecture describes how

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the system has actually been built. So it's based

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on observing the system as it is and extracting

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the architecture from the observation. This is what we call

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the as-implemented software architecture. And one key point here is

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that often, these two architectures, the prescriptive and the descriptive

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architectures end up being different. So let's see why that happens.