A Rationale-based Model for Architecture Design Reasoning

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8.3. Other applications of ARM of architecture design options can be performed. The estimations or the expectations given by architects are subjective in nature. EC and EB are subjectively expected utilities because the cost, benefit and risk measurements are all subjective assessment by an architect. CBAM [4] and ArchDesigner [2] provide a similar quantitative approach to rank important decisions. ARM differs to these approaches in that the quantitative rationale in ARM is risk-based. Although ARM’s assessment is subjective in nature, we posit that experienced architects could improve risk estimation because analysis methodology such as CMMI can be performed to refine their estimations over many projects. This feedback loop could improve the decision making process and identify areas where design estimations are inferior. 8.3 Other applications of ARM As discussed earlier, ARM can assist architects to reason with decisions by exploring, assessing and documenting design options. It can be used to supplement design methodologies such as object-oriented modelling and database modelling techniques. With ARM, two other applications to support software development are now possible: (a) the scope of architecture design can be ambiguous because it is difficult to determine when architecture design is complete and when other design activities should take over. Section 8.3.1 describes how ARM is used to delineate architecture design activities from detailed design activities; (b) using architecture rationale, the architecture design can be verified by examining the design reasoning. This is described in 8.3.2. 8.3.1 Completeness of architecture design Software architecture is concerned with the structure of a software system. Its objectives and activities are different to that of detailed software design. The need for such distinction lies in the role of the architects and the need for its verification. There is currently no agreed definition on the amount of details that are required in architecture modelling in order to satisfy the objectives of constructing an architecture. Instead of using Intensional and Non-local properties [37] to distinguish architecture activities, we propose a method for distinguishing architecture activities from detailed design activities based on the level of risks. The level of risks represents the uncertainty of the architecture model to meet its requirements [19]. The less uncertainty in an architecture design the more confident an architect is about the design. 143
8.3. Other applications of ARM As discussed in Section 8.2.2, architects provide estimates for Outcome Certainty Risk (OCR) and Implementation Certainty Risk (ICR) at each decision point. OCR represents the uncertainties of meeting the outcome objectives set out in the functional or nonfunctional requirements. This risk may arise because of a number of reasons: • Functional or non-functional requirements may be ambiguous and need to be clarified or redefined. • A design may have an impact on certain aspects of some non-functional requirements and the extent of that impact is unknown. • Certain external environmental factors may have an impact on the implementation of the requirements and the extent of that impact is unknown. • Assumptions need to be made about different aspects of the system such as business requirements, project environment or technologies. ICR represents the uncertainties in implementing the design. This risk may arise for the following reasons: • Technical feasibility of the implementation. • Uncertainty due to the complexity of the design. • Uncertainty due to a lack of experience, knowledge or skills of the development team. These two types of risks may be resolved through iterations of refinement and architecture design. ARM records and analyses these risks by using quantitative design rationale OCR and ICR. The risks can be estimated and progressively reduced to an acceptable threshold as architecture design progresses and design details become available. The certainty that the architecture model could satisfy the requirements would increase. When this certainty level reaches a pre-defined threshold for all architectural requirements and designs, we regard that the architecture model is complete. Different requirements in the system post different levels of risks. The level of design details required in various parts of an architecture model vary depending on the level of risk. For instance, a reusable item with a well defined behaviour and interface does not require additional in-depth architecture design. On the other hand, requirements which are complex in nature or have extensive non-functional requirement implications may need further investigation into its technical feasibility and explore more details of the design 144
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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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3.4. Other related studies evolutio
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3.5. How well design rationale meth
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3.5. How well design rationale meth
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Chapter 4 Research methodology and
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4.1. Software engineering research
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4.2. The chosen research and valida
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Part II Architecture Design Rationa
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on a regular basis. Their inputs ha
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5.1. Architecture rationale in the
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5.2. Survey methodology data collec
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5.3. Survey findings experience). I
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5.3. Survey findings Table 5.1: Fre
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5.3. Survey findings Business Goals
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5.3. Survey findings 5.3.5 Document
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5.3. Survey findings Table 5.8 summ
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5.3. Survey findings We used Spearm
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5.3. Survey findings previous desig
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5.4. Discussion of findings Since t
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5.4. Discussion of findings or cons
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5.5. Limitations and use design rat
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Part III The Representation and App
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6.1. A conceptual model for design
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6.2. Architecture Rationale and Ele
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6.2. Architecture Rationale and Ele
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6.3. Architecture elements Figure 6
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6.4. Architecture rationale Figure
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Page 113 and 114: 6.4. Architecture rationale depicts
Page 115 and 116: 6.5. The extended AREL To prevent c
Page 117 and 118: 6.6. A UML representation of AREL a
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Page 121 and 122: 6.7. AREL usability AE by ≪AEsupe
Page 123 and 124: 6.8. Summary The AREL model is exte
Page 125 and 126: 7.1. The EFT system reasoning, a co
Page 127 and 128: 7.1. The EFT system The processing
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Page 139 and 140: 7.1. The EFT system Figure 7.10: De
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Page 153 and 154: 8.1. Background Based on these assu
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Page 189 and 190: 10.2. Building a BBN to represent a
Page 197 and 198: 10.3. Reasoning about change impact
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Page 211 and 212: 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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