cs540 software design lecture 2 1 lecture 2: software design methods anita s. malik...

CS540 Software Design Lecture 2 1

Lecture 2: Lecture 2: Software Design Software Design

MethodsMethodsAnita S. MalikAnita S. Malik

[email protected]@umt.edu.pk

Adapted fromAdapted from Budgen (2003) Chapter 3 and Budgen (2003) Chapter 3 and Schach (2002) Chapter 1Schach (2002) Chapter 1

CS540 Software Design 2Lecture 2

Recap – Lecture 1Recap – Lecture 1 Design (Verb): Process of DesignDesign (Verb): Process of Design Design (Noun): Result of the Design Design (Noun): Result of the Design

Process, a blue print for the system to be Process, a blue print for the system to be developeddeveloped

Design Process in non-analyticalDesign Process in non-analytical Software Design Phase takes the ‘what’ Software Design Phase takes the ‘what’

part and produces the ‘how’ part; takes part and produces the ‘how’ part; takes system from ‘problem’ domain to system from ‘problem’ domain to ‘solution’ domain‘solution’ domain

Software Design is perhaps the most Software Design is perhaps the most critical factor affecting the quality of the critical factor affecting the quality of the system; it has a major impact on later system; it has a major impact on later phases particularly maintenancephases particularly maintenance


Software Design MethodsSoftware Design Methods

Design methods provide guidelines Design methods provide guidelines on the choices to be made during the on the choices to be made during the design processdesign process

Structured Methods, Formal Structured Methods, Formal Methods and Object-Oriented Methods and Object-Oriented MethodsMethods


What Support do Design What Support do Design Methods Provide?Methods Provide?

Knowledge transfer mechanismKnowledge transfer mechanism Common standards, guidelines, techniques, Common standards, guidelines, techniques,

criteria and goals to be used by the entire criteria and goals to be used by the entire design teamdesign team

Recording decisions and reasons in a Recording decisions and reasons in a systematic mannersystematic manner

Make sure all factors involved in a problem Make sure all factors involved in a problem are considered (all design elements can be are considered (all design elements can be traced to some requirements)traced to some requirements)

Identify important progress milestonesIdentify important progress milestones


Why Methods Don’t Work Why Methods Don’t Work Miracles?Miracles?

Design methods provide guidance and adviceDesign methods provide guidance and advice By focusing on a particular domain of By focusing on a particular domain of

problems e.g., data-processing, real time problems e.g., data-processing, real time systems, it is possible to provide tighter systems, it is possible to provide tighter guidance.guidance.

Cooking recipe analogy – designing a Cooking recipe analogy – designing a software is like writing a cooking recipesoftware is like writing a cooking recipe

Most methods are applied to different Most methods are applied to different domains to optimize their use that results domains to optimize their use that results from familiarity with methodfrom familiarity with method


Software Life-cycleSoftware Life-cycle

1.1. Requirements phaseRequirements phase

2.2. Specification phaseSpecification phase

3.3. Design phaseDesign phase

4.4. Implementation phaseImplementation phase

5.5. Integration phase (in parallel Integration phase (in parallel with 4)with 4)

6.6. Maintenance phaseMaintenance phase

7.7. RetirementRetirement


Software Development Software Development ProcessProcess

If institutionalized can constrain If institutionalized can constrain creativity rather than support itcreativity rather than support it

Many forms and variations of Many forms and variations of development processdevelopment process

Presence of feedback loops between Presence of feedback loops between the various stages of software the various stages of software processprocess


Linear Development Linear Development ProcessProcess

Mainly based on the waterfall modelMainly based on the waterfall model Provides a strong management Provides a strong management

framework for planning, monitoring framework for planning, monitoring and controllingand controlling

Transform model and its limitations Transform model and its limitations (Formal approaches)(Formal approaches)


Incremental Development Incremental Development Process (non linear Process (non linear

process)process) Limitations of linear development Limitations of linear development

processprocess Prototypes – constructed to explore Prototypes – constructed to explore

an idea more completely before the an idea more completely before the actual construction startsactual construction starts EvolutionaryEvolutionary ExperimentalExperimental ExploratoryExploratory

Reactive developmentReactive development


Context for DesignContext for Design

Ref: (Fig 3.1 Chapter 3 Budgen 2003)Ref: (Fig 3.1 Chapter 3 Budgen 2003)

Regardless of how the software Regardless of how the software development tasks are organized, development tasks are organized, design is strongly linked to the tasks design is strongly linked to the tasks that precede it – Requirements that precede it – Requirements Specification and AnalysisSpecification and Analysis


Approximate Relative Cost of Each Approximate Relative Cost of Each PhasePhase 1976–1981 data1976–1981 data

Maintenance constitutes 67% of total costMaintenance constitutes 67% of total cost


Good and Bad SoftwareGood and Bad Software

Good software is maintained—bad Good software is maintained—bad software is discardedsoftware is discarded

Different types of maintenanceDifferent types of maintenance Corrective maintenance [about 20%]Corrective maintenance [about 20%] EnhancementEnhancement

Perfective maintenance [about 60%]Perfective maintenance [about 60%] Adaptive maintenance [about 20%]Adaptive maintenance [about 20%]


Specification and Maintenance Specification and Maintenance FaultsFaults

60 to 70 percent of faults are 60 to 70 percent of faults are specification and design faultsspecification and design faults

Data of Kelly, Sherif, and Hops [1992]Data of Kelly, Sherif, and Hops [1992] 1.9 faults per page of specification1.9 faults per page of specification 0.9 faults per page of design0.9 faults per page of design 0.3 faults per page of code0.3 faults per page of code


Specification and Maintenance Specification and Maintenance Faults (contd)Faults (contd)

Data of Bhandari et al. [1994] - Faults Data of Bhandari et al. [1994] - Faults at end of the design phase of the new at end of the design phase of the new version of the productversion of the product 13% of faults from previous version of 13% of faults from previous version of

productproduct 16% of faults in new specifications16% of faults in new specifications 71% of faults in new design71% of faults in new design


Cost to Detect and Correct a Cost to Detect and Correct a FaultFault


Structured ParadigmStructured Paradigm The structured paradigm had great The structured paradigm had great

successes initiallysuccesses initially It started to fail with larger products (> It started to fail with larger products (>

50,000 LOC)50,000 LOC) Maintenance problems (today, up to 80% Maintenance problems (today, up to 80%

of effort)of effort) Reason: structured methods are Reason: structured methods are

Action oriented (finite state machines, data Action oriented (finite state machines, data flow diagrams); or flow diagrams); or

Data oriented (entity-relationship diagrams, Data oriented (entity-relationship diagrams, Jackson’s method);Jackson’s method);

But not bothBut not both


The Object-Oriented Paradigm The Object-Oriented Paradigm (contd)(contd)

Both data and actions are of equal Both data and actions are of equal importanceimportance

Object: Object: Software component that incorporates both Software component that incorporates both

data and the actions that are performed on data and the actions that are performed on that datathat data

Example:Example: Bank accountBank account

Data:Data: account balanceaccount balance Actions: Actions: deposit, withdraw, determine balancedeposit, withdraw, determine balance


Structured versus Object-Structured versus Object-

Oriented ParadigmOriented Paradigm

Information hiding Information hiding Responsibility-driven designResponsibility-driven design Impact on maintenance, developmentImpact on maintenance, development


Key Aspects of Object-Oriented Key Aspects of Object-Oriented SolutionSolution

Conceptual independenceConceptual independence EncapsulationEncapsulation

Physical independence Physical independence Information hidingInformation hiding

Impact on developmentImpact on development Physical counterpartPhysical counterpart

Impact on maintenanceImpact on maintenance Independence effectsIndependence effects


Responsibility-Driven Responsibility-Driven DesignDesign

Also called “Design by Contract”Also called “Design by Contract” Send flowers to your aunt in Iowa CitySend flowers to your aunt in Iowa City

Call 1-800-FLOWERSCall 1-800-FLOWERS Where is 1-800-FLOWERS?Where is 1-800-FLOWERS? Which Iowa City florist does the delivery?Which Iowa City florist does the delivery? Information hidingInformation hiding

Object-oriented paradigmObject-oriented paradigm ““Send a message to a method [action] of Send a message to a method [action] of

an object“an object“


Transition From Analysis to Transition From Analysis to DesignDesign

Structured paradigm:Structured paradigm: Sharp transition between analysis (what) and design Sharp transition between analysis (what) and design

(how)(how) Object-oriented paradigm:Object-oriented paradigm:

Objects enter from very beginningObjects enter from very beginning


Analysis/Design “Hump”Analysis/Design “Hump”

Systems analysisSystems analysis Determine what has to be doneDetermine what has to be done

DesignDesign Determine how to do itDetermine how to do it Architectural design—determine Architectural design—determine

modulesmodules Detailed design—design each moduleDetailed design—design each module


Removing the “Hump”Removing the “Hump”

Object-oriented analysisObject-oriented analysis Determine what has to be doneDetermine what has to be done Determine the objectsDetermine the objects

Object-oriented designObject-oriented design Determine how to do itDetermine how to do it Design the objectsDesign the objects


In More DetailIn More Detail

Objects enter hereObjects enter here


WarningWarning Do not use the object-paradigm to enhance a Do not use the object-paradigm to enhance a

product developed using the structured product developed using the structured paradigmparadigm Water and oil do not mixWater and oil do not mix

Exception: if the new part is totally disjointException: if the new part is totally disjoint Example: adding a GUI (graphical user interface)Example: adding a GUI (graphical user interface)

cs540 software design lecture 2 1 lecture 2: software design methods anita s. malik...

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