A Rationale-based Model for Architecture Design Reasoning

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9.3. Traceability support 9.3 Traceability support General traceability provides a means to retrieve related development artefacts such as system requirements and design objects. However, architecture verification and enhancement are better served if design rationale is traceable as well. Without design rationale, implicit assumptions, constraints and design reasoning can only be derived by secondguessing, or they might be overlooked altogether, and as such the risk that architects are not able to correctly verify or maintain the architecture design exists. The AREL model provides a mean to represent the causal and the dependency relationships between design rationale and design objects. Such representation provides an additional perspective to understand the relationships between design objects and their design rationale. The tracing is therefore characterised by the inter-connections of design rationale and design objects using these causal relationships. Constraints, assumptions, decisions and tradeoffs can be traced to disparate parts of a system that they influence. There are three possible tracing techniques: forward tracing, backward tracing and evolutionary tracing. They rely on the AREL and eAREL links ≪ARtrace≫, ≪AEsupersede≫ and ≪ARsupersede≫. • Forward Trace - the purpose of this trace is to support the impact analysis of the architecture design. For example, an architect might use forward trace to find all the design objects that originate from a requirement, and the reasons behind their design. Given an architecture element AE 1 , all architecture rationale and architecture elements that are downwardly caused and impacted by AE 1 can be traversed. • Backward Trace - the purpose of this trace is to support the root-cause analysis of the architecture design. For example, an architect may use it to analyse what requirements and factors influence a design object and the reasons why. For a given architecture element AE 1 , all decisions and other architecture elements that AE 1 depends on, directly or indirectly, are traced and retrieved. This enables architects and designers to retrieve the root causes such as requirements and assumptions of AE 1 , and to understand and analyse design justifications leading to AE 1 . • Evolution Trace - the purpose of this trace is to support the analysis of the evolution of a decision or an architecture element. Given a AR 1 or AE 1 node, the history containing previous versions of the node is retrieved. The traceability support based on the AREL model has two characteristics. Firstly, it provides an automated mechanism to support forward and backward tracing. An architect could specify the source of the trace (i.e. an AE), and the system would traverse all related 155
9.4. AREL and eAREL traceability applications in a case study elements in the AREL model. Enterprise Architect [150] is the UML design tool we use to capture the AREL model, the results of a trace are created as UML diagrams. Secondly, traceability can be selective based on architecture elements’ classifications. Using the classification of the architecture elements by viewpoints and business drivers (see Section 6.3), architects could limit the trace results to the specified types of architecture elements. For instance, a trace could traverse only those AEs that are specific to the data viewpoint. The classification-based traceability could reduce information overload when analysing trace results. This is an initial attempt to implement the traceability scoping with classified architecture elements. It demonstrates that classification is useful in restricting the scope of the trace results. 9.4 AREL and eAREL traceability applications in a case study Using the case study as a basis, we demonstrate the advantages of being able to explain and trace the architecture from the design reasoning perspective. It provides important information that are missing from most design specifications in which the focus is on design organisation, interface and behaviour. In the demonstration, we choose the processing services and specifically the payment message processing layer to illustrate the rationalebased architecture model and its traceability below. We demonstrate the traceability with the AREL tool-set. The tool-set comprises of an UML-based tool called Enterprise Architect and a tool for AREL tracing. A detailed description of the tool implementation is in Chapter 11. 9.4.1 Design rationale representation This section recapitulates an example from the case study in Chapter 7 to demonstrate the traceability techniques. The EFT system had extensive design specifications to document what had been designed. However, they do not systematically document the assumptions, constraints and rationale of the design. Its specifications document the design of the software modules, their interfaces and behaviour. Designers who were not originally involved in the design would find it difficult to understand the design intentions. Thus, when system modifications are required, it would be hard to determine which parts of the system are affected. We use the payment messaging mechanism as an example to illustrate how a traceable AREL model captures this knowledge. 156
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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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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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