A Rationale-based Model for Architecture Design Reasoning

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6.4. Architecture rationale textual form which is easier to enter and understand. • Causal Relationship Chain - since AR acts as a connector between the cause architecture elements and the resulting architecture elements, we can construct a graphical representation showing direct dependencies between architecture elements and decisions in a chain. Such relationships can then be analysed to understand the design reasoning. This is an improvement over template-based design rationale methods because they do not link the design artefacts to design rationale in a chain of causal relationships. It is also an improvement over some of the argumentation-based methods such as gIBIS and QOC where design artefacts are not represented. The encapsulation of architecture rationale in AR provides reasoning support to help architects understand a design decision and allow them to verify the decision. Relating AR to architecture elements AE provides the knowledge about the inter-dependency between architecture elements. It solves the problem of not being able to understand the design because of implicit assumptions and constraints. 6.4.1 Qualitative rationale During the deliberation of design decisions, a number of factors have to be considered. Issues surrounding a decision need to be specified and alternative options to solving the issues are considered. Each alternative is assessed for its strengths and weaknesses. Some tradeoffs might be necessary in the decision making process. QLR is a template within AR to capture such qualitative design rationale. There has been substantial research on this subject by [94, 97, 23, 170, 3], we utilise some of their results as a basis for the qualitative design reasoning of QLR. Additionally, we have verified the design rationale elements through the survey reported in Chapter 5. The following information are contained in QLR: • issue of the decision - the issue specifies the concern of this decision. • design assumptions - they document the unknowns that are relevant to this decision. • design constraints - the constraints that are specific to this decision. • strengths and weaknesses of a design. • tradeoffs - they document the analysis of what is a more appropriate alternative by using priorities and weightings. 91
6.4. Architecture rationale • risks and non-risks - they are considerations about the uncertainties or certainties of a design option. • assessment and decision - they summarise the decision and the key justifications behind the selection or exclusion of a design. • supporting information - decision maker(s), stakeholder(s), date of decision, revision number and history. The information contained in QLR provides the qualitative rationale to justify a decision. It helps architects and designers to understand the reasons and the justifications behind a decision. 6.4.2 Quantitative rationale For most architecture design, the decision making process is based on the experience and the intuition of architects. Design tradeoffs are often not explicitly quantified. The lack of a quantifiable justification makes it very difficult to subsequently assess the quality and accuracy of design decisions using quality approaches such as CMMI. Quantitative rationale enables systematic estimates of the expected return of design alternatives. The expected return of a decision is represented by the architect’s estimate of the Cost Benefit Ratio (CBR) at a decision point. The QNR approach is based on three elements - cost, benefit and risk. It is measured by an index rating. The reasons for using an index instead of money terms are because (a) some of the assessment cannot be expressed in money terms for they may be intangible or difficult to estimate; (b) there may be multiple factors in which their benefits or costs values cannot be easily combined; (c) the comparison between design options can be made using the same scale; (d) it provides a uniform measure for reviews and verification. The quantitative measures comprises of the following items: • Architecture Cost Index (ACI) - measures the relative cost of a decision with a rating between 1 and 10. • Architecture Benefits Index (ABI) - measures the relative benefit of a decision with a rating between 1 and 10. • Outcome Certainty Risk (OCR) - measures the risk that the outcome would not satisfy the intended goal(s) with a probability between 0 and 1. 92
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A Rationale-based Model for Archite
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maintenance. These techniques can h
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Declaration This thesis contains no
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2.2.6 DoD Architecture Framework .
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5.4.6 Risk assessment in architectu
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8.2 The architecture rationalisatio
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12.2 Contributions . . . . . . . .
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6.10 ≪AR≫ and ≪AAR≫ Stereot
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11.13A Process to Synchronise Chang
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5.13 Design Rationale Helps Evaluat
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that architecture design is highly
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1.2. Research motivations and resea
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1.2. Research motivations and resea
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1.4. Structure of the thesis the ch
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Part I Problem Analysis 10
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2.1. Industry practice of design ra
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2.2. Architecture frameworks and de
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Chapter 3 Related work in design ra
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3.2. Why do we need design rational
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3.2. Why do we need design rational
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3.3. Existing methods for capturing
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3.4. Other related studies 3.3.7 Qu
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Page 99 and 100: Part III The Representation and App
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8.2. The architecture rationalisati
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8.3. Other applications of ARM As d
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8.3. Other applications of ARM Figu
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8.3. Other applications of ARM area
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Chapter 9 Architecture rationale an
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9.1. Background 9.1 Background In t
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9.2. Traceability of architecture r
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9.4. AREL and eAREL traceability ap
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Chapter 10 Architecture decision de
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10.1. Background 10.1.2 Introductio
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10.2. Building a BBN to represent a
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10.3. Reasoning about change impact
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10.5. Summary design object may cau
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11.1. Capturing architecture design
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11.1. Capturing architecture design
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11.2. Checking AREL models Figure 1
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11.3. Tracing AREL models Figure 11
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11.4. Analysing AREL with BBN • S
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11.5. Limitations Figure 11.13: A P
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Chapter 12 Conclusions 12.1 Summary
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12.2. Contributions reasoning metho
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12.2. Contributions implementations
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12.3. Future work architecture deci
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12.3. Future work to examine the co
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BIBLIOGRAPHY [10] B. W. Boehm, Soft
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BIBLIOGRAPHY [37] A. Eden and R. Ka
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BIBLIOGRAPHY [62] J. D. Herbsleb an
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BIBLIOGRAPHY [89] N. Lassing, D. Ri
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BIBLIOGRAPHY [115] D. L. Parnas,
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BIBLIOGRAPHY [142] Z. Simsek and J.
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BIBLIOGRAPHY [167] W. F. Tichy, N.
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Appendix A AREL Tool User Manual 1
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4.1 AREL Check Model When the Check
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4.2 AREL Model Tracing AREL model t
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Figure 9 - result of downward trace
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To initiate the graph’s creation,
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onto the diagram 14 Assign values t
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Useful Definitions The following ar
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) Some projects only c) Not at all
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19. I revisit architecture design d
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Complaint Procedure If you have any
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Privacy Protection Only investigato
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B. Exploring design reasoning. 1. W
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3. Why does the system use asynchro
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C. General Comments on AREL Modelli
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IEEE Computer Society Press. A. Tan
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