A Rationale-based Model for Architecture Design Reasoning

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10.2. Building a BBN to represent an AREL model If an AE becomes volatile, then the decision which uses the AE as an input may not be as reliable because it is probable that a change in the underlying AE input could invalidate the design decision. As such, we need to represent the possible validity of the AR decision. The two states of an AR node are: • Valid – the decision is valid • Invalid – the decision is invalid 10.2.2 Edges: Representing causal relationships Each ≪ARtrace≫ link in an AREL model is represented by an edge in the BBN. As AREL links are defined to preclude directed cycles, this means that the corresponding BBN is valid, i.e. it is a directed acyclic graph. When an AREL model is formed, it is based on interconnected nodes with the fundamental structure of AE i → AR j → AE k . This structure represents the directional causal relationship between the nodes starting from AE i . AEs as motivational reasons drive decisions to create high-level design. The high-level design are refined and decomposed into finer-grained architecture design objects through making further decisions for the different aspects of the architecture such as data models, application models and technology models. This process of making decisions, creating and modifying architecture elements is carried out in a progressive way until the architecture is complete [159]. Figure 10.2: Basic Forms of AREL Relationship in the BBN The three basic forms of relationships that are present in the BBN representation of the AREL model are shown in Figure 10.2: 2 2 In the BBN literature, (A) and (C) are referred to common effect structures, while (B) is a common cause structure. We distinguish between (A) and (C) here because of the difference for our purposes between the AE and AR nodes as a common effect. 171
10.2. Building a BBN to represent an AREL model A. AEs as causes of an AR : AE1 and AE2 are converging inputs of AR1 ; B. AEs as effects of an AR : AE4 and AE5 are effects of AR1 ; C. Multiple ARs as causes of an AE : AE5 depends on both AR1 and AR2. The fundamental AE i → AR j → AE k structure reflects the fact that a decision (represented by an AR node) depends on its input AEs, and in turn can affect other AEs as the outcomes of the decision. At this stage, we can see intuitively that the edges in the BBN can represent the important causal relationships between AEs and ARs, such as: • while the input AE nodes are stable, a decision will probably remain valid; • if the input AE nodes have changed, then it is likely that the conditions under which the decision was made are no longer valid and a reassessment of the inputs is necessary to validate the decision; • the validity or otherwise of an AR node affects the stability of a consequent AEs. These relationships are defined and quantified through the specification of the CPTs. We describe this aspect of the BBN knowledge engineering process next, first for the root nodes, and then for non-root nodes in relationships A, B and C above. 10.2.3 Probabilities: Quantifying the causal relationships Root Nodes Each root node in a BBN (i.e. nodes without parents) has an associated prior probability. As mentioned above, in a BBN representation of an AREL model, all root nodes must be of type AE, and represent either functional or non-functional requirements, basic designs or systems constraints. The architect must therefore estimate the prior probabilities for the different types of AE nodes. Prior probabilities assigned to the AE root nodes indicate the likelihood of change of these primary requirements, design or constraints. If the AE is a requirement, one could estimate whether this requirement is volatile or stable by assessing whether the requirement is likely to change over time. For instance, an industry standard or a regulation is not negotiable and therefore the probability of its being stable is 100% and the probability of its being volatile is 0%. Another example is the requirement to produce data through different interface file formats such as XMI, 172
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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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6.4. Architecture rationale • ris
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6.4. Architecture rationale depicts
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6.5. The extended AREL To prevent c
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6.6. A UML representation of AREL a
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6.6. A UML representation of AREL a
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6.7. AREL usability AE by ≪AEsupe
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6.8. Summary The AREL model is exte
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7.1. The EFT system reasoning, a co
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7.1. The EFT system The processing
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7.1. The EFT system not chosen beca
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7.1. The EFT system Figure 7.5: Int
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7.1. The EFT system sequence checki
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7.1. The EFT system Figure 7.7: Dec
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7.1. The EFT system Therefore, in a
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Page 215 and 216: 11.2. Checking AREL models Figure 1
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Page 223 and 224: Chapter 12 Conclusions 12.1 Summary
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Page 233 and 234: BIBLIOGRAPHY [10] B. W. Boehm, Soft
Page 235 and 236: BIBLIOGRAPHY [37] A. Eden and R. Ka
Page 237 and 238: BIBLIOGRAPHY [62] J. D. Herbsleb an
Page 239 and 240: 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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