A Rationale-based Model for Architecture Design Reasoning

6.2. Architecture Rationale and Elements Linkage (AREL)
as an architecture element, to show its influence on a decision. This is similar to a goal in
DRL.
A decision creates and is justified by the architecture design rationale, similar to the
argument in REMAP. The architecture rationale encapsulates the details of the justification.
It contains a description of the issues addressed by the decision, the arguments
for and against an option, and the alternative options that have been considered. Once
a decision is made, the result of a decision is a design outcome or solution. A design
outcome should be explicitly represented in the architecture design as an architecture
element. Although this conceptual model has similarities, such as the representation of
design rationale and design issues, to other design rationale models, it is unique because
it simplifies the argumentation aspect and strengthens the linkage between motivational
reasons, design rationale and design elements. This subject is further discussed in Section
6.2.
6.2 Architecture Rationale and Elements Linkage (AREL)
The AREL model is an implementation of the conceptual model using the UML notation
[118, 113]. AREL is an acyclic graph which relates architecture elements AEs to architecture
rationale ARs using directional links ARtrace. An AE is an architecture element
that participates in a decision as an input (i.e. motivational reason) or an outcome (i.e.
design outcome). They are stereotyped by ≪AE≫. An AR encapsulates the architecture
design justification of a decision. ARs are stereotyped by ≪AR≫. Since AR has a oneto-one
relationship to justify a decision, AR can therefore represent a decision point in
AREL modelling. The relationships between an AE and an AR are connected by a directional
association stereotyped ≪ARtrace≫. It is also referred to as a links in the AREL
definition below. The ≪ARtrace≫ stereotype is used to represent the causal relationships
between AEs and ARs. A causal relationship is a relationship between two entities where
AE is a cause and AR is the effect. For instance, a motivational reason causes a decision
to be made. Alternatively, AR is a cause and AE is an effect. For instance, a decision
causes a design object to be created as an effect.
Definition 1 An Architecture Rationale and Element Linkage (AREL) model is a tuple
(AE, AR, P L), where AE is a set of nodes representing architecture elements, AR is a set
of nodes representing architecture rationales, and P L ⊆ (AE × AR) ∪ (AR × AE) is a set
of directed links between the nodes, such that
1. all rationale nodes must be associated by links with at least one cause and one effect:
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