software engineering principles principles form the basis of methods, techniques, methodologies and...
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Software Engineering Principles
Principles form the basis of methods, techniques, Principles form the basis of methods, techniques, methodologies and toolsmethodologies and tools
Seven important principles that may be used in Seven important principles that may be used in all phases of software developmentall phases of software development
Apply to the software product as well as the Apply to the software product as well as the development processdevelopment process
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Key principlesKey principles
Rigor and formalityRigor and formality Separation of concernsSeparation of concerns ModularityModularity AbstractionAbstraction Anticipation of changeAnticipation of change GeneralityGenerality IncrementallyIncrementally
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Rigor and formalityRigor and formality
Software engineering is a creative design Software engineering is a creative design activity, BUT It must be practiced systematicallyactivity, BUT It must be practiced systematically
Rigor is a necessary complement to creativity Rigor is a necessary complement to creativity that increases our confidence in our that increases our confidence in our developmentsdevelopments
Formality is rigor at the highest degreeFormality is rigor at the highest degree
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Examples: Rigor and formalityExamples: Rigor and formality
Product:Product: – – Formal-Mathematical analysis of program Formal-Mathematical analysis of program
correctnesscorrectness – – Rigorous-Systematic test data derivation Rigorous-Systematic test data derivation • • Process:Process: – – Rigorous- detailed documentation of each Rigorous- detailed documentation of each
development step in waterfall modeldevelopment step in waterfall model – – Formal- automated transformational process to Formal- automated transformational process to
derive program from formal specificationsderive program from formal specifications
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Separation of concerns
To dominate complexity, separate the issues to To dominate complexity, separate the issues to concentrate on one at a timeconcentrate on one at a time
– – "Divide & conquer""Divide & conquer" Supports parallelization of efforts and separation Supports parallelization of efforts and separation
of responsibilitiesof responsibilities
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Examples:Examples:
Process: Go through phases one after the other Process: Go through phases one after the other as in waterfall Modelas in waterfall Model
––Do separation of concerns by separating Do separation of concerns by separating activities with respect to timeactivities with respect to time
– – Product: Keep different types of product Product: Keep different types of product requirements separaterequirements separate
––Functionality discussed separately from the Functionality discussed separately from the performance constraintsperformance constraints
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ModularityModularity
A complex system may be divided into simpler A complex system may be divided into simpler pieces called modulespieces called modules
• • A system that is composed of modules is called A system that is composed of modules is called modularmodular
• • Supports application of separation of concernsSupports application of separation of concerns – – when dealing with a module we can ignore when dealing with a module we can ignore
details of other modulesdetails of other modules
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Modularity: Cohesion and Modularity: Cohesion and couplingcoupling Each module should be highly cohesiveEach module should be highly cohesive – – module understandable as a meaningful unitmodule understandable as a meaningful unit – – Components of a module are closely related to Components of a module are closely related to one anotherone another • • Modules should exhibit low couplingModules should exhibit low coupling – – modules have low interactions with othersmodules have low interactions with others – – understandable separatelyunderstandable separately
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Abstraction
Identify the important aspects of a phenomenon Identify the important aspects of a phenomenon and ignore its detailsand ignore its details
– – Special case of separation of concernsSpecial case of separation of concerns – – The type of abstraction to apply depends on The type of abstraction to apply depends on
purposepurpose • • Example: the user interface of a watch (its Example: the user interface of a watch (its
buttons) abstracts from the watch's internals for buttons) abstracts from the watch's internals for the purpose of setting time; other abstractions the purpose of setting time; other abstractions needed to support repairneeded to support repair
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Anticipation of change
Ability to support software evolution requires Ability to support software evolution requires anticipating anticipating
potential future changespotential future changes ––It is the basis for software evolvabilityIt is the basis for software evolvability
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Generality
While solving a problem, try to discover if it is an While solving a problem, try to discover if it is an instance of a more general problem whose instance of a more general problem whose solution can solution can
be reused in other cases be reused in other cases • • Sometimes a general problem is easier to solve Sometimes a general problem is easier to solve
than a special casethan a special case ––Carefully balance generality against Carefully balance generality against
performance and costperformance and cost
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Incrementality
Process proceeds in a stepwise fashion Process proceeds in a stepwise fashion (increments)(increments)
• • Examples (process)Examples (process) – – deliver subsets of a system early to get early deliver subsets of a system early to get early
feedback from expected users, then add new feedback from expected users, then add new features incrementallyfeatures incrementally
– – deal first with functionality, then turn to deal first with functionality, then turn to performanceperformance
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A Layered A Layered TechnologyTechnology
Software Engineering
a “quality” focusa “quality” focus
process modelprocess model
methodsmethods
toolstools
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A Process A Process FrameworkFramework
Process frameworkProcess frameworkFramework activitiesFramework activities
work taskswork taskswork productswork productsmilestones & deliverablesmilestones & deliverablesQA checkpointsQA checkpoints
Umbrella ActivitiesUmbrella Activities
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Framework ActivitiesFramework Activities
CommunicationCommunication PlanningPlanning ModelingModeling
Analysis of requirementsAnalysis of requirements DesignDesign
ConstructionConstruction Code generationCode generation TestingTesting
DeploymentDeployment
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Umbrella ActivitiesUmbrella Activities Software project managementSoftware project management Formal technical reviewsFormal technical reviews Software quality assuranceSoftware quality assurance Software configuration managementSoftware configuration management Work product preparation and Work product preparation and
productionproduction Reusability managementReusability management MeasurementMeasurement Risk managementRisk management
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The Process Model:The Process Model:AdaptabilityAdaptability
the framework activities will the framework activities will alwaysalways be be applied on applied on everyevery project ... BUT project ... BUT
the tasks (and degree of rigor) for each the tasks (and degree of rigor) for each activity will vary based on:activity will vary based on: the type of project the type of project characteristics of the projectcharacteristics of the project common sense judgment; concurrence of the common sense judgment; concurrence of the
project teamproject team
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The CMMIThe CMMI Capability Maturity Model Integration (CMMI) – Capability Maturity Model Integration (CMMI) –
developed by The Software Engineering Institute developed by The Software Engineering Institute (SEI)(SEI)
The CMMI defines each process area in terms of The CMMI defines each process area in terms of “specific goals” and the “specific practices” required “specific goals” and the “specific practices” required to achieve these goals.to achieve these goals.
Specific goalsSpecific goals establish the characteristics that establish the characteristics that must exist if the activities implied by a process area must exist if the activities implied by a process area are to be effective. are to be effective.
Specific practicesSpecific practices refine a goal into a set of process-refine a goal into a set of process-related activities.related activities.
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The CMMIThe CMMI
Level 0: Incomplete - Level 0: Incomplete - Process goals not satisfiedProcess goals not satisfied Level 1: Performed - Level 1: Performed - Process goals satisfiedProcess goals satisfied Level 2: Managed - Level 2: Managed - Process areas conforms to Process areas conforms to
organizationally defined policy, resources are organizationally defined policy, resources are available, work tasks are monitoredavailable, work tasks are monitored
Level 3: Defined - Level 3: Defined - Tailored according to the Tailored according to the organization’s standard processesorganization’s standard processes
Level 4: Quantitatively managed - Level 4: Quantitatively managed - Quantitative Quantitative assessmentassessment
Level 5: Optimized - Level 5: Optimized - Processes are optimizedProcesses are optimized
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Process PatternsProcess Patterns Process patterns define a set of activities, Process patterns define a set of activities,
actions, work tasks, work products and/or related actions, work tasks, work products and/or related behaviorsbehaviors
A template is used to define a patternA template is used to define a pattern Typical examples:Typical examples:
Customer communication (a process activity)Customer communication (a process activity) Analysis (an action)Analysis (an action) Requirements gathering (a process task)Requirements gathering (a process task) Reviewing a work product (a process task)Reviewing a work product (a process task) Design model (a work product)Design model (a work product)
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Process AssessmentProcess Assessment
The process should be assessed to ensure that it The process should be assessed to ensure that it meets a set of basic process criteria that have meets a set of basic process criteria that have been shown to be essential for a successful been shown to be essential for a successful software engineeringsoftware engineering.
Many different assessment options are available: Many different assessment options are available: SCAMPISCAMPI CBA IPICBA IPI SPICESPICE ISO 9001:2000ISO 9001:2000
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Assessment and ImprovementAssessment and Improvement
Software Process
Software Process Assessment
is examined by identifies capabilitiesand risk of
identifiesmodifications to
Software Process Improvement
Capability Determination
leads to leads to
motivates
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Personal Software Process Personal Software Process (PSP)(PSP)
Recommends five framework activities:Recommends five framework activities: PlanningPlanning High-level designHigh-level design High-level design reviewHigh-level design review DevelopmentDevelopment PostmortemPostmortem
stresses the need for each software stresses the need for each software engineer to identify errors early and as engineer to identify errors early and as important, to understand the types of important, to understand the types of errorserrors
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Team Software Process (TSP)Team Software Process (TSP)
Each project is “launched” using a “script” Each project is “launched” using a “script” that defines the tasks to be accomplishedthat defines the tasks to be accomplished
Teams are self-directedTeams are self-directed Measurement is encouragedMeasurement is encouraged Measures are analyzed with the intent of Measures are analyzed with the intent of
improving the team processimproving the team process
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