Notice that the arrows do not all flow from the right to the left. In fact, most of them point from left to right. This is because the architecture is following the Dependency Rule. All dependencies cross the boundary lines in one direction, and they always point toward the components containing the higher-level policy. Also notice that the using relationships (open arrows) point with the flow of control, and that the inheritance relationships (closed arrows) point against the flow of control. This depicts our use of the Open–Closed Principle to make sure that the dependencies flow in the
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