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And there are two important and related concepts that

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have to do with the way software architecture

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evolves. The first one is Architectural Drift, which is

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the introduction of architectural design decisions that are orthogonal to

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a system's prescriptive architecture. That is, they're not included

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in, encompassed by, or implied by the prescriptive architecture.

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And the result of Architectural Drift is that you

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start from a clean architecture, like the one that I'm

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showing here, and then you start adding pieces without following a clear plan.

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Like, for example, here, we add an additional room here, but we don't really

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do it in the right way so we need to add something else

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to keep it stable. And then maybe we want some more room so we

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add a tent. And then another side of the house, it doesn't really

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follow the same architecture but it doesn't matter, we just put it there because

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we want to expand. And maybe then we want to put something classic

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there, even though it doesn't really fit

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the overall design and the overall architecture.

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So I think you get my point, the fact

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that the architecture then becomes unnecessarily complex, hard to understand

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and ultimately awkward, just like the one that I'm

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showing here, that goes from the original building into this

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final monstrosity. The second concept is Architectural Erosion, which

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is the introduction of architectural design decisions that violate a

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system prescriptive architecture. So in this case, that we were

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introducing decisions that were orthogonal,

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here, were introducing this decisions

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that don't comply with the prescriptive

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architecture. And the result of Architectural Erosion

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is typically a poor architecture an

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architecture that is going to have problems in

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the future. So both Architectural Drift

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and Architectural Erosion take you away in

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different ways from what you think your software architecture is or should be.