software processes - university of denvermysite.du.edu/~lbarne28/se/slides/ch4.pdf · these are not...

Software Processes

Adapted from Ian Sommerville 2006, Software Engineering, 8th edition. Chapter 4 1

ObjectivesObjectives

To introduce software process models To introduce software process models To describe three generic process models and

when they may be usedy y To describe outline process models for

requirements engineering, softwared l t t ti d l tidevelopment, testing and evolution

To explain the Rational Unified Process modelTo introduce CASE technology to support To introduce CASE technology to supportsoftware process activities


Topics coveredTopics covered

Software process models Software process models Process iteration

Process activities Process activities The Rational Unified Process

C t id d ft i i Computer-aided software engineering


The software processThe software process

A structured set of activities required to develop a A structured set of activities required to develop asoftware system• Specification;• Design;• Validation;• Evolution.

A software process model is an abstractrepresentation of a process It presents a descriptionrepresentation of a process. It presents a descriptionof a process from some particular perspective.


Generic software process modelsGeneric software process models The waterfall model The waterfall model

• Separate and distinct phases of specification anddevelopment.

E l ti d l t Evolutionary development• Specification, development and validation are

interleaved. Component-based software engineering

• The system is assembled from existing components.Th i t f th d l f l There are many variants of these models e.g. formaldevelopment where a waterfall-like process is usedbut the specification is a formal specification that is


p prefined through several stages to an implementabledesign.

Waterfall modelWaterfall model


Waterfall model phasesWaterfall model phases

Requirements analysis and definition Requirements analysis and definition System and software design Implementation and unit testing Implementation and unit testing Integration and system testing Operation and maintenancep The main drawback of the waterfall model is the

difficulty of accommodating change after thei d O h h t bprocess is underway. One phase has to be

complete before moving onto the next phase.


Waterfall model problemsp

Inflexible partitioning of the project into distinct Inflexible partitioning of the project into distinctstages makes it difficult to respond to changingcustomer requirements.

Therefore, this model is only appropriate when therequirements are well-understood and changes willb f i l li it d d i th d ibe fairly limited during the design process.

Few business systems have stable requirements.The waterfall model is mostly used for large systems The waterfall model is mostly used for large systemsengineering projects where a system is developed atseveral sites.


Evolutionary developmentEvolutionary development

Exploratory development Exploratory development• Objective is to work with customers and to evolve a

final system from an initial outline specification.y pShould start with well-understood requirements andadd new features as proposed by the customer.

Th t t i Throw-away prototyping• Objective is to understand the system requirements.

Should start with poorly understood requirements toShould start with poorly understood requirements toclarify what is really needed.



Problems Problems• Lack of process visibility;• Systems are often poorly structured;Systems are often poorly structured;• Special skills (e.g. in languages for rapid prototyping)

may be required. Applicability

• For small or medium-size interactive systems;• For parts of large systems (e.g. the user interface);• For short-lifetime systems.


Component-based software engineeringp g g

Based on systematic reuse where systems are Based on systematic reuse where systems areintegrated from existing components or COTS(Commercial-off-the-shelf) systems.

Process stages• Component analysis;

R i t difi ti• Requirements modification;• System design with reuse;• Development and integration.p g

This approach is becoming increasingly used ascomponent standards have emerged.


Reuse-oriented developmentp


Process iteration

System requirements ALWAYS evolve in the System requirements ALWAYS evolve in thecourse of a project so process iteration whereearlier stages are reworked is always part of theg y pprocess for large systems.

Iteration can be applied to any of the genericpp y gprocess models.

Two (related) approaches• Incremental delivery;• Spiral development.


Incremental deliveryy

Rather than deliver the system as a single delivery, Rather than deliver the system as a single delivery,the development and delivery is broken down intoincrements with each increment delivering part of the

i d f ti litrequired functionality. User requirements are prioritised and the highest

priority requirements are included in earlypriority requirements are included in earlyincrements.

Once the development of an increment is started,Once the development of an increment is started,the requirements are frozen though requirements forlater increments can continue to evolve.


Incremental developmentp


Incremental development advantagesp g

Customer value can be delivered with each Customer value can be delivered with eachincrement so system functionality is availableearlier.

Early increments act as a prototype to help elicitrequirements for later increments.q

Lower risk of overall project failure. The highest priority system services tend tog p y y

receive the most testing.


Extreme programmingp g g

An approach to development based on the An approach to development based on thedevelopment and delivery of very smallincrements of functionality.y

Relies on constant code improvement, userinvolvement in the development team andppairwise programming.

Covered in Chapter 17


Spiral developmentp p

Process is represented as a spiral rather than as Process is represented as a spiral rather than asa sequence of activities with backtracking.

Each loop in the spiral represents a phase in the Each loop in the spiral represents a phase in theprocess.

No fixed phases such as specification or design - No fixed phases such as specification or designloops in the spiral are chosen depending on whatis required.

Risks are explicitly assessed and resolvedthroughout the process.


Spiral model of the software processSpiral model of the software process


Spiral model sectorsp

Objective setting Objective setting• Specific objectives for the phase are identified.

Risk assessment and reduction• Risks are assessed and activities put in place to reduce

the key risks. Development and validation Development and validation

• A development model for the system is chosen whichcan be any of the generic models.

Pl i Planning• The project is reviewed and the next phase of the spiral

is planned.


Process activities

Software specification Software specification Software design and implementation

Software validation Software validation Software evolution


Software specificationp

The process of establishing what services are The process of establishing what services arerequired and the constraints on the system’soperation and development.p p

Requirements engineering process• Feasibility study;y y;• Requirements elicitation and analysis;• Requirements specification;• Requirements validation.


The requirements engineering processThe requirements engineering process


Software design and implementationg p

The process of converting the system The process of converting the systemspecification into an executable system.

Software designg• Design a software structure that realises the

specification;Implementation Implementation• Translate this structure into an executable program;

The activities of design and implementation are The activities of design and implementation areclosely related and may be inter-leaved.


Design process activitiesg p

Architectural design Architectural design Abstract specification

Interface design Interface design Component design

D t t t d i Data structure design Algorithm design


The software design processg p


Structured methods

Systematic approaches to developing a software Systematic approaches to developing a softwaredesign.

The design is usually documented as a set ofg ygraphical models.

Possible models• Object model;• Sequence model;• State transition model;State transition model;• Structural model;• Data-flow model.


Programming and debuggingg g gg g

Translating a design into a program and Translating a design into a program andremoving errors from that program.

Programming is a personal activity - there is no Programming is a personal activity there is nogeneric programming process.

Programmers carry out some program testing to Programmers carry out some program testing todiscover faults in the program and remove thesefaults in the debugging process.


The debugging processgg g p


Software validation

Verification and validation (V & V) is intended to Verification and validation (V & V) is intended toshow that a system conforms to its specificationand meets the requirements of the system

tcustomer. Involves checking and review processes and

system testingsystem testing. System testing involves executing the system

with test cases that are derived from thespecification of the real data to be processed bythe system.


The testing processg p


Testing stagesg g

Component or unit testing• Individual components are tested independently;• Components may be functions or objects or coherent

groupings of these entitiesgroupings of these entities. System testing

• Testing of the system as a whole. Testing ofg y gemergent properties is particularly important.

Acceptance testingT ti ith t d t t h k th t th t• Testing with customer data to check that the systemmeets the customer’s needs.


Testing phasesg p


Software evolution

Software is inherently flexible and can change Software is inherently flexible and can change. As requirements change through changing

business circumstances the software thatbusiness circumstances, the software thatsupports the business must also evolve andchange.g

Although there has been a demarcation betweendevelopment and evolution (maintenance) this isincreasingly irrelevant as fewer and fewersystems are completely new.


System evolutiony


The Rational Unified Process

A modern process model derived from the work A modern process model derived from the workon the UML and associated process.

Normally described from 3 perspectives Normally described from 3 perspectives• A dynamic perspective that shows phases over time;• A static perspective that shows process activities;p p p ;• A practive perspective that suggests good practice.


RUP phase modelp


RUP phasesp

Inception Inception• Establish the business case for the system.

Elaboration Elaboration• Develop an understanding of the problem domain

and the system architecture. Construction

• System design, programming and testing. Transition

• Deploy the system in its operating environment.


RUP good practiceg p

Develop software iteratively Develop software iteratively Manage requirements

Use component based architectures Use component-based architectures Visually model software

V if ft lit Verify software quality Control changes to software


Static workflows

Wor kflow Description

Busines s mode lling The bu sines s proce sses are mode lled u sing bu sines s use case s.

Requi rements Actors who interact with the system are iden tified and use cases ar edeve loped to mode l the system requirements.

Ana lysis and de sign A des ign mode l is created and do cumented u sing a rchitecturaly g g gmode ls, componen t mode ls, obj ect mode ls and sequ ence mod els.

Implementation The co mpon ents in the system are implemented and structured intoimplementation sub- systems . Au tomatic code gen eration from designmode ls helps accelerate this proces s.

T t T ti i it ti th t i i d t i j ti ithTest Testing is an iterative p roce ss that is ca rried ou t in con junc tion withimplementation. System testing follows the completion of theimplementation.

Dep loyment A produc t releas e is created, distributed to us ers and installed in theirworkplace .

Con figuration andchang e manag ement

This suppo rting workflow managed change s to the system (seeChapter 29) .

Project manag ement This suppo rting workflow manage s the system deve lopment (seeChapter 5) .


Envi ronment This work flow is con cern ed with making app ropr iate software toolsava ilable to the software deve lopment team.

Computer-aided software engineeringp g g

Computer-aided software engineering (CASE) is Computer-aided software engineering (CASE) issoftware to support software development andevolution processes.

Activity automation• Graphical editors for system model development;• Data dictionary to manage design entities;• Graphical UI builder for user interface construction;• Debuggers to support program fault finding;• Debuggers to support program fault finding;• Automated translators to generate new versions of a

program.


Case technologygy

Case technology has led to significant Case technology has led to significantimprovements in the software process. However,these are not the order of magnitudegimprovements that were once predicted• Software engineering requires creative thought - this

is not readily automated;• Software engineering is a team activity and, for large

projects much time is spent in team interactionsprojects, much time is spent in team interactions.CASE technology does not really support these.


CASE classification

Classification helps us understand the different types Classification helps us understand the different typesof CASE tools and their support for processactivities.

Functional perspective• Tools are classified according to their specific function.

Process perspective• Tools are classified according to process activities that

are supportedare supported. Integration perspective

• Tools are classified according to their organisation into


Tools are classified according to their organisation intointegrated units.

Functional tool classification

T l t E lTool type Examples

Planning tools PERT tools, estimation tools, spreadsheets

Editing tools Text editors, diagram editors, word processors

Ch t t l R i t t bilit t l h t l tChange ma nagement tools Requirements traceability tools, change c ontrol systems

Configuration management tools Version m anagement systems, sys tem b uilding tools

Prototyping tools Very h igh-level languages, user interface generators

Method support tools Design editors data dictionaries code generatorsMethod-support tools Design editors, data dictionaries, code generators

Language-processing tools Com pilers, interprete rs

Program analysis tools Cross reference generators, static analysers, dynamic analysers

Testing tools Test data generators file comparatorsTesting tools Test data generators, file comparators

Debugging tools Interactive debugging systems

Documentation tools Page l ayout programs , image editors

Re engineering tools Cross reference systems program re structuring system s


Re-engineering tools Cross-reference systems, program re-structuring system s

Activity-based tool classificationy


CASE integrationg

Tools Tools• Support individual process tasks such as design

consistency checking, text editing, etc. Workbenches

• Support a process phase such as specification ordesign Normally include a number of integrateddesign, Normally include a number of integratedtools.

Environments• Support all or a substantial part of an entire software

process. Normally include several integratedworkbenches.


Tools workbenches environmentsTools, workbenches, environments


Key pointsy p

Software processes are the activities involved in Software processes are the activities involved inproducing and evolving a software system.

Software process models are abstractt ti f threpresentations of these processes.

General activities are specification, design andimplementation, validation and evolution.implementation, validation and evolution.

Generic process models describe the organisation ofsoftware processes. Examples include the waterfall

d l l ti d l t d tmodel, evolutionary development and component-based software engineering.

Iterative process models describe the software


Iterative process models describe the softwareprocess as a cycle of activities.

Key pointsy p

Requirements engineering is the process of Requirements engineering is the process ofdeveloping a software specification.

Design and implementation processes transform theifi ti t t blspecification to an executable program.

Validation involves checking that the system meetsto its specification and user needs.to its specification and user needs.

Evolution is concerned with modifying the systemafter it is in use.

The Rational Unified Process is a generic processmodel that separates activities from phases.

CASE technology supports software process


CASE technology supports software processactivities.

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