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A Rationale-based Model for Architecture Design Reasoning

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9.4. AREL and eAREL traceability applications in a case study<br />

Figure 9.4: Backward tracing <strong>for</strong> root-cause analysis<br />

9.4.3 Tracing architecture design evolution<br />

Since architectures can have a long live-span and are subject to enhancements and adaptations<br />

over time, the view of the current architecture design does not necessarily provide all<br />

the in<strong>for</strong>mation required <strong>for</strong> decision making. We use eAREL as a supporting mechanism<br />

<strong>for</strong> evolution tracking. It provides a means to track changes of the design and the decision<br />

making over time. Let us consider architecture element C4 2 5 <strong>for</strong> MAC Processing. In<br />

Figure 9.5(a), assuming I1 1 5 and R2 4 6 are the new requirements to support authenticity<br />

of the payment message using an encryption mechanism. The implementation requires<br />

the MAC code to be encrypted with a secret key to prove its authenticity. So the original<br />

design C4 2 5, which only supports clear-text MAC, would require some modifications.<br />

We decide to keep its original design history.<br />

A copy of the original design, i.e. version 1 of C4 2 5 is archived and a relationship<br />

of the stereotype ≪AEsupersede≫ links it with version 2 of the C4 2 5, which is in the<br />

current AREL model. This is shown in Figure 9.5(b). Since version 1 of C4 2 5 MAC has<br />

now been replaced, its ≪ARtrace≫ links to AR12 and AR13 are now obsolete, there<strong>for</strong>e<br />

these links are made non-current. New ≪ARtrace≫ links are created to be related to<br />

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