A Rationale-based Model for Architecture Design Reasoning

12.2. Contributions
is no common understanding on how to measure risks, and the risk assessment process in
architecture design is not well understood. It suggests that further investigation in this
area is required.
It has been found that the methodology and tool support for design rationale capture
and retrieval is inadequate. The various tools that have been reported, including word
processors and UML-based tools, do not have traceability features to support systematic
design rationale description and retrieval. Therefore, it is important to understand how
best to capture, represent and use design rationale and then develop tools to provide a
design rationale enabled development environment.
In summary, the survey has allowed us to gain an in-depth understanding of the application
of design rationale in the software industry. It has confirmed that even architects
consider them to be useful, there is little in terms of methodology and tools to support
their applications. The survey has established the need to further study architecture design
rationale, and clarified a number of important research questions that we address in
this thesis.
12.2.2 Design rationale representation
In this thesis, we have introduced a rationale-based architecture model (AREL) to represent
architecture design rationale. The AREL model uses two types of reasoning support:
motivational reasons and design rationale. Motivational reasons induce architecture issues
that need to be resolved. Architecture design decisions are justified by architecture
design rationale which is comprised of qualitative rationale, quantitative rationale and
alternative design options. In an architecture design, intricately inter-dependent design
objects often have common requirements, assumptions, constraints and decisions. They
can be explicitly related and reasoned in AREL models. This reasoning support complements
the documentation of design structures and interfaces commonly appeared in design
specifications.
AREL captures two types of design rationale: qualitative design rationale QLR and
quantitative design rationale QNR. QLR represents the reasoning and the arguments,
in a textual form, for and against a design decision. QNR uses indices to indicate the
relative costs, benefits and risks of design options. Together they can help architects justify
architecture decisions. This representation is an improvement over the argumentationbased
methods because it simplifies the representation of qualitative argumentation, and
provides quantification to justify why a design is chosen over its alternatives. The AREL
model is extended by eAREL to support design evolution. Both AREL and eAREL
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