A Rationale-based Model for Architecture Design Reasoning

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9.4. AREL and eAREL traceability applications in a case study and AR13 which consider message sequencing and missing payment message detection respectively. Normally a payment acknowledgement should arrive shortly after a payment has been sent, but if it does not arrive within the allowed elapsed time, there ought to be a time-out function to indicate that the acknowledgement is missing. AR15 is a decision to implement such an Alarm Server to notify any overdue acknowledgement. This example of forward tracing shows the impacts of a requirement to all the design objects and decisions that are affected by it. The design decision AR10 creates a chain effect on the resulting design branching out into many decisions and design outcomes. AREL forward tracing has a number of characteristics: • Impact analysis - when an architecture element AE 1 is specified, the architecture rationale (AR) and the architecture elements (AE) that depends on AE 1 are retrieved. Since AREL is a causal model, it implies that all resulting architecture decisions and elements are directly or indirectly impacted by AE 1 . • Selection by viewpoints - the classification of architecture elements by architecture viewpoints allows architects to hone in on specific results by specifying what is required. • Graphical representation - since AREL is implemented in UML, trace results are also represented in UML diagrams. Backward tracing In this section, we discuss the methods for backward tracing in AREL and demonstrate how to carry out backward tracing. Backward tracing in AREL is the traversal of the AREL graph to produce a subset of the resulting AREL graph backward from a specified AE node. The following steps are involved in the backward tracing of AREL: 1. Specify a source AE node, say AE 1 , where tracing is to begin. 2. Specify the scope of the result set using the viewpoint classification (e.g. Business Viewpoint). 3. For all the ancestors of the source node AE 1 , traverse the AE and AR nodes recursively to all the root nodes by following the reverse direction of the ARtrace links. Since the AREL model is an acyclic graph, the traversal will terminate when all root nodes have been traversed. 161
9.4. AREL and eAREL traceability applications in a case study 4. All the AE nodes with the specified viewpoint classification(s) will be retained in the result set. 5. All the AE nodes that are not specified in the classification, but are located between AE 1 and its ancestor AE nodes that are in the classification are retained. Similar to forward tracing, if these unspecified nodes are not traversed, then the causal chain will be broken and some of the required AE nodes downstream from it would be omitted. Using the example from the previous section, we demonstrate backward tracing of the root-causes of the alarm server. Consider the Alarm Server C6 0 0, if we want to understand why it is there, and what requirements have motivated the architects to create it, then we trace backwards from it. The resulting AREL graph is shown in Figure 9.4. It shows all the requirements, design elements and design decisions that lead to the creation of C6 0 0. The reason for the creation of C6 0 0 is due to the need of a timer mechanism (AR15 ) to support asynchronous error detection C4 2 7. The timer would time-out and send a notification if a payment message has not been acknowledged within a specified time. The justification in AR15 specifies that this ought to be a separate server process because there is a technical constraint to implement time-out in the payment processing process itself. By tracing further backwards, we understand that the need for such implementation is due to the No Loss of Payment Transaction requirement. This requirement comes from R2 5 1 as well as the implementation of C4 2 4. C4 2 4 is in turn concerned with the performance issue of the payment system. If an architect wants to assess the possibilities of enhancing the timer server, the first task is to understand the causes of such a design. These causes are intricate because there are underlying constraints and assumptions in a chain of dependency. In this case, the multitude of constraints are performance (AR10 ), reliability(AR14 ) and technical implementation(AR15 ). A change in the design must address all these inter-connected causes and constraints at the same time. Similar to forward traceability, backward traceability supports results scoping by viewpoints. The resulting trace is a subset of the AREL model. Backward traceability supports root-cause analysis by retrieving architecture rationale and architecture elements for which the design element in question directly or indirectly depends on. 162
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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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Page 171 and 172: 9.1. Background 9.1 Background In t
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Page 215 and 216: 11.2. Checking AREL models Figure 1
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Page 219 and 220: 11.4. Analysing AREL with BBN • S
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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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