A Rationale-based Model for Architecture Design Reasoning

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7.2. An empirical study to validate the AREL model 7.2.4 Empirical study results In this section, we describe the results of the study. The empirical study relies on a panel of experts to reason about the architecture with and without the aid of the AREL model. The experts may use the original design specifications, recall from memory, make deduction or make guesses to answer the questions. After the initial analysis of the design reasoning, a comparison is made to see if additional reasoning could be gained with the AREL model. Experts were asked questions in four areas of the architecture design. These areas are described in the case study sections of this chapter. The following sections discuss each set of questions and the answers that have been provided by the experts. Question 1 - Fault resilient support This question asks about the fault-resilient feature of the EFT system and the reasons for having this design. The design reasoning is described in Section 7.1.2. Table 7.1 presents an analysis of how experts recall the design rationale. The column on documentation indicates that some of the information comes from a documented source such as specifications. Memory indicates that the experts remember the reasons. This source of information is not as reliable because the experts may remember wrongly or incompletely. Deduction is what the experts reconstruct as design rationale based on documented and memory sources. Guessing is what the experts suspect of the reasoning based on experience. There are no facts to support the reasoning of guesses. An expert may use more than one means to reason about the design. Table 7.1: Empirical study - Question 1 Results Documentation Memory Deduction Guess Responses 6 3 4 2 In 7.1, 6 experts could find the answers from the specifications that describe what fault-resilient mechanisms are provided by the system. This is because the mechanisms are clearly documented in the design specifications. Based on which, most experts have deduced and guessed the design rationale without much trouble. The experts were able to describe application recovery, dual-node support for fault resiliency and communication backup mechanisms. The AREL model presented to the experts confirmed their answers. AREL provided additional items which have been missed by most of the experts. Examples are the power failure and site failure of the system. 125
7.2. An empirical study to validate the AREL model Question 2 - Software layering Question 2 asks why there are three layers of software in the EFT design and whether this is important to the architecture design. This design is described in Section 7.1.3 of the case study. Most experts could not find the relevant description in the architecture design specification (see Table 7.2). However, most experts could recall or deduce that the layering of software is due to the modularity and flexibility requirements of the software. Some experts mentioned the separation of concerns would help maintenance and produce a “cleaner” design. Table 7.2: Empirical study - Question 2 Results Documentation Memory Deduction Guess Responses 1 5 6 3 When the experts were asked as to why there are three different UNIX processes with each process supporting a separate software layer, none of the experts could find a reason in the documentation. They deduced that it was due to the need to support different communication protocols. Some of the experts queried the legitimacy of this design. AREL was shown to the experts to explain that the original design was influenced by an external factor. The EFT system was meant to be a product to eventually support national payment systems, and an international panel of experts at the time dictated that the three layers of software have to be physically separate and hence the EFT design followed such architecture. Using the architecture design reasoning approach, some experts have pointed out that this design is not necessarily the best approach. This is because having three physical UNIX processes means that two different communication protocols are required to support them. This necessarily increase the complexity of the EFT system without additional benefits. It would have been better if the messaging and communication layers are combined to form a single process. As such, both flexibility and the performance are maintained. The architecture design would be simplified. In this case, the AREL architecture rationale have facilitated discussions and arguments for the purpose of architecture design validation. Question 3 - Asynchronous messaging We ask the experts what the reasons are for selecting asynchronous communication instead of synchronous communication, in which the design is described in Figure 7.5. All experts suggested that this is somehow due to performance reason. 126
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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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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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