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REQUIREMENTS, ARCHITECTURE AND RISKSVahid Jalali

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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OUTLINE

Motivations Basis for the approach DDP

Standard Revised

KWIC DDP Matrixes Conclusion

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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MOTIVATIONS

Architecture plays a prominent role in large, complex software systems

Selection of an appropriate architecture is critically important development step

Software design for complex software system is difficult

Risk-based reasoning helps in making good architectural decisions

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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BASIS FOR THE APPROACH

Defect Detection and Prevention (DDP) Requirements Risks Mitigations

Steps in Standard DDP Collection and weighting of requirements Determining the risks these requirements entail Listing activities that can mitigate risks

DDP is a quantitative risk-based approach

Requirements

RisksMitigation

s

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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STANDARD DDP PROCESSDetermine and weight

Requirements

Determine Resources

List Potential

Risks

List & Cost Relevant

Mitigations

Score Risks against

Requirements

Score Mitigations

against Risks

Select Cost-Effective

Mitigations

Development Plan

Descope/ Reprioritize Requirements

Revise Budget, etc

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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SHORTCOMINGS OF STANDARD DDP

Distinction between mitigation and design decision

Some mitigations induce and/or exacerbate risks Induce

Induced risks have a range in [-1,0) Exacerbate

Exacerbate risks have a range in [-1000000,-1)

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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REVISED DDP PROCESSDetermine and weight

Requirements

Determine Resources

List Potential Risks

List Relevant Architectures

Score Risks against

Requirements

Score Architectures against Risks

Select Software

Architecture

List Potential Risks

List & Cost Relevant

Mitigations

Score Risks against

Architecture

Score Mitigations

against Risks

Select Cost-Effective

Mitigations Risk Mitigation Plan

Revise Budget, etc

Descope/ Reprioritize Requirements

Revise selection of architecture

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A CASE STUDY

KWIC The KWIC index system accepts an ordered set of lines each line is an ordered set of words each word is an ordered set of characters Any line may be "circularly shifted" by repeatedly removing

the first word and appending it at the end of the line The KWIC index system outputs a listing of all circular shifts

of all lines in alphabetical order

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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Shared data architecture

DESIGN ALTERNATIVES

Master Control

InputCircular

ShiftAlphabetizer Output

Characters

IndexAlphabetized

index

Input mediumOutput medium

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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Abstract data type architecture

Alphabetic ShiftsCircular ShiftCharacters

DESIGN ALTERNATIVES (CONT.)

Master Control

Input Output

Input Medium

Output Medium

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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Pipes-and-filters architecture

Input

DESIGN ALTERNATIVES (CONT.)

Input medium

Circular shift

Alphabetizer

OutputOutput medium

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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DDP MATRIXES

Risk-Architecture

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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DDP MATRIXES (CONT.)

Risk-Mitigation

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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CONCLUSION

Risk can and should be used to guide architectural decisions Choice of architecture Decisions flow from the choice

DDP framework is proposed for addressing these problems

Guidelines for checklist in making risks and mitigations quantitative?

Effect of complexity of project on DDP? Nonfunctional requirements?

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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REFERENCE

James Kiper and Martin Feather, "Requirements, Architectures and Risks", Proceedings of the Second International Workshop “From Software Requirements to Architectures” (STRAW’03) at the International Conference on Software Engineering, May 2003, pp. 100-106

Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007

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Amirkabir university of technology, Department of computer engineering and information technology, Intelligent systems laboratory, http://ceit.aut.ac.ir/islab, Requirement engineering course, Fall 2007