topic 3 software process models

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Humboldt University Berlin, University of Novi Sad, University of Plovdiv,University of Skopje, University of Belgrade, University of Niš, University of Kragujevac

DAAD Project“Joint Course on Software Engineering”

Version: Oct. 29, 2005 (D Nov. 06, 2003)

Topic 3Software process models

2DAAD project „Joint Course on Software Engineering“ ©

3. Process models

a) Why process models?

b) Overview of existing models

c) Classical and iterative phase model (waterfall model)

d) Alternative phases in phase models

e) Prototyping

f) Spiral model

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Process models: used terminology

(Note: terms are similar, but with differences; e.g. life cycle model: development and maintenance, software development model: without maintenance)

Software process modelsPhase modelsLife cycle modelsSoftware development modelsProject models


Why process models ?

„SE is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software ...“(IEEE Standard Glossary of Software Engineering Terminology, 1990).

Definition of the term SE requires studying models for systematic software development (main objective of SE)!

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Relevance of process modelsProcess models are relevant for

Project organization:• Otherwise: sporadic,

uncoordinated project management

• Experience: high-quality SW is impossible without a systematic approach to SW development

Project analysis:What are the weak points in the development process?

Time and cost planning

Qualitative assessment of SW companiesCertification for ISO 9000


What is a process model ?

Process model• In general: Development plan, which specifies the

general process of developing a software product.• More precisely: Definition that states, which activities

are to be performed, by which person, acting in which role; in which order the activities will be performed, and which products will be developed and how to evaluate them.

Role• coworker, who accomplish a certain activity

e.g. test engineer, project leader, design specialist, programmer, software ergonomist

What isSW-specific?

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Performing an activity: basic scheme (activity = subprocess of a process model)

Source: Balzert, vol. 1, p. 60

Givenartifacts

Role XCoworker Y

Tools

Changed or new artifact

Legend:

Activity

Role

Coworker

Model(Artifact)

Document(Artifact)

Methods•Guidelines•Conventions•Check lists•Samples


Software artifacts

Software artifact• Product of art created by humans• Can be a document, a model or a program • Examples :

- Document, e.g. requirements specification- Model, e.g. OOA model - Program, e.g. C++-Program.

Software product• Set of software artifacts

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3. Process models





e) Prototyping

f) Spiral model


Most familiar process models: Overview

Process models

• Classical phase model(waterfall model)

• Iterative phase model(life cycle)

• Spiral model

• Prototyping(evolutionary SE)

• V-model

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Notes

Models are always idealized, they give only a framework and must allow flexible working

must not hinder workDifferent classes of SW development problems

different suitable models

e.g. AI program: gradual evolutionPrototyping model is often used


3. Process models





e) Prototyping

f) Spiral model

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Software development process until 1970: considered as a black box

Software development process

Program

code

What happens inside?

Only until 1970?

Customer

informal requirements


Analysisand

Definition

Analysisand

Definition

The classical waterfall model (1970)

DesignDesign

ImplementationImplementation

TestTest

Usage and MaintenanceUsage and

Maintenance

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Phases of SW development:subject and products (overview)

Analysis and DefinitionAnalysis of the problem + Definition of the requirements to the SW, focus: external behavior of the SW system intensive cooperation: client ↔ contractor

requirement specifications, product model and othersDesignSpecification of the structure of the SW (software architecture), specification of components and their relations

software architecture, detailed design, and othersImplementationSoftware architecture is „filled out“: programming of the components

program (code)TestTesting of the components, testing of their integration

test cases, test protocols and others


Analysisand

Definition

Analysisand

Definition

The classical waterfall model (1970)

DesignDesign


TestTest


Maintenance

Problems ?

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Documents of SW development

Required features (empty circles) got lost, unnecessary (filled circles) are added

Source: Schneider, SEUH 43, p. 123

Customer Analyst Designer Programmer

Customer's requests

Specification Design Code


Information flow in SW projects

How the customerexplained it

How the Project Leader understood it

How theTesterleft it

How the Programmerwrote it

How the Business Consultant described it

How the project was documented

How the Software architect designed it

How the customerwas billed

How it was supported What the customerreally needed So

urce

: unk

now

n

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Analysisand

Definition

Analysisand

Definition

Iterative phase model

DesignDesign


TestTest


Maintenance

Problems ?


Cost allocation in the software life cycle

Maintenance67%

Requirement analysis

3%

Specification3% Design

5%

Coding7%

Unit Testing

8%

IntegrationTesting

7%

Source: R. Klösch, H.Gall: Objektorientiertes Reverse Engineering. Springer, 1995

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Error statistics: occurrence and correction

Source: Software Metrics Symposium 1996, p. 176

requirements design implementation

20 % 38 % 42 %

1 % 2 % 20 % 30 % 40 % 7 %

requirementsreview

designreview

code review

+unittest

subsystem test

system and acceptance

test

field faults

faults detected

faults introduced to the software


3. Process models





e) Prototyping

f) Spiral model

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Phases according to Jacobson

Jacobson: Object-oriented Software Engineering p. 32

Characteristics ?

Requirementsanalysis

Preliminarydesign

Detaileddesign

Coding

Unit testing

Integration

System test


Phases according to Denert

Denert: Software Engineering, Springer Verlag, 1992, p. 39

System Specification

User Interface

Data model

Functional Model

System Construction

Modularity

Process organization

Database design

Module Implementation

Module specification

Moduletesting

Module construction

System Integration

Subsystem definition

System testing

Subsystem testing

Characteristics ?

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RequirementsDefinition Design

DetailedConcept

SoftwareDesign

organization hierarchyorganization hierarchy

rough data model

task processes

task hierarchy

userinterfacedesign

function processes

function hierarchy

data model

Problem Analysis

RequirementsDefinition

Design Implementation,Integration & Test

RoughConcept

DetailedConcept

SoftwareDesign

SoftwareSystem

Client/ServerOS/2, MotifMS-WindowsUNIX/RDBs

SNI BS2000COBOL, UTMSESAM, UDS

IBM MVSCOBOL, CICSDB2IMS DB/DC

database model

interface specificationComponent SKONTO is connected with the

aaaaaaaaaSKONTO is

aaaaaaaaaaaaBATT

aaaaaaaaaaaaLOOKUP

integration model

DB definitions, SQL ...

GUI objects

program logicIF kunde = 99999CASE PlaubaTT = 1

IF kunde = nnnnnnn

PlaubaTT, I

system model

Phases in CASE-Tool MAESTRO II

SEtec Process Model

SEtec Result ModelSource: SoftLab, Munich, MAESTRO II (most well-known German CASE-Tool)

Characteristics ?


Unified Software Development Process (USDP)

Process of object-oriented software development due to Jacobson, Booch, Rumbaugh (1999)

Requirements

Analysis

Design

Implementation

Test

Part of the phase ‚Analysis and Definition‘, in which the basic use cases of the systems will be detected:

use case diagrams

Part of the phase ‚Analysis and Definition‘, in which the basic classes of the problem will be detected:

class diagrams

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Phases according to Balzert

Balzert: Textbook of Software Technology vol. 1, 2001

Introduction and Overview

1 Fundamentals 2 Object-orientedEnterprise Modelling

V Enterprise Modelling

I SW-Management

1 Bases

2 Planing

3 Organization

4 Personal

5 Leadership

6 Control

III SW-Quality Assurance

1 Bases

2 Quality Assurance

3 Manual Proof Methods

4 Process Quality

5 Product Quality –Components

6 Product Quality –System

1 Planning phase

2 Definition phase

3 Design phase

4 Implementation phase

5 Acceptance and Introduction

6 Maintenance phase

I SW-Development

4 Reorganization3 Re-use2 CASE1 Principles andMethods

IV Cross-sections and Views


1 Planning phase

2 Definition phase

3 Design phase

4 Implementation phase

5 Acceptance and Introduction

6 Maintenance phase

I SW-Development

Characteristics ?

Phases according to Balzert(detail)

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Phase model in the Space shuttle Program (NASA)

Facts:• 22 releases (versions, OI = Operational Increment) 1981-2001• development until 2020• each year: a new release• for each release: 2 years development time• several releases at the same time in process• strong effects to project management

Source: M. Zelkovitz, I. Rus: ICSM 2001, p. 119

1990

ValidationMission Preparation

Operational lifetime

1992 1994 1996 1998 2000

Q

O

M

K

IO

I Rel

ease Development

Lifecycle for each OI (Operational Increment)


Project

Design

ConstructionProduction planning

Preparation of work

Production

Test

Contract Begin of production Delivery

1 YearSource: R.Bronsart, SEUH 1996

Special phase model

What is remarkable ?

How to be interpreted?

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Phase model of

Samsonite


Test of suitcases ☺

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3. Process models





e) Prototyping

f) Spiral model


PrototypingOperational area:Requirements imprecise at the beginning and/or constantly changed

Prototype:runable software system,• Substantial parts of the final product already finished

(e.g. user interface, basic behavior),• Other parts still to be done (e.g. ineffective, special cases)

Application cases:• Prototype (may be thrown away)

(addition of the requirement analysis : rapid prototyping)• Advancement to the final product

(evolutionary software development)

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Phases of iterative prototyping

Boyle: Design of Multimedia Learnnig, Prentice Hall Europe (1997), p. 186

Design a solution

Establish theProblem Spaces

ImplementSolution

SummativeEvaluation & Delivery

Evaluate

Characteristics ?


Requirements

Analysis

Design

Implementation

EvaluationEvaluationEvaluation

Dynamic Systems Development Method (DSDM)

Standard non-proprietary RAD method based upon user-driven iterative prototyping (1995)

Feasibility and business study

Placing the system in user environment

Functional prototype iterationsDesign prototype iterations

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3. Process models





e) Prototyping

f) Spiral model


Introduction to spiral modelProblem analysis:• goals• alternatives

Risk analysis:• evaluation of

alternatives

Realization:• construction of the product• test

Planning:• next project steps

Review

Characteristics of the phases?

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Spiral model due to Boehm (1988)

determination of goals, alternatives and additional requirements of a newspiral cycle

evaluation of alternatives;identification and reduction of risks

planning of next steps, i.e. of the next spiral cycle

construction and test of the current product

end of cycle: Review

project progressin the spiral cycle

Risk analysis:Problem analysis:

Realization:Planning:


The essence of the spiral model

abstract model: meta modelabstraction from other models of SW development(one turn = • one phase or

• development of next prototype or ...)

orients to similar activities of each step (problem analysis, risk analysis, realization, planning, review)risk analysis: comparison of possible alternatives(examples: selection of a programming language, of the A-&D-method, of the staff, usage of tools)

flexible:first turn produce prototypes, next turns correspond to the phasesA&D, design, ...

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The phase model as a special case of the spiral model

Pagel, Six p.72

Risk analysis

Operation andmaintenance

R e v i e w sales forecast

Project planPlanning ofanalysis phase

GUI-prototype

Simulation

Analysis

Validation ofproduct definition

Softwaredesign

Codingand

unit test

Integrationand

system test Installation

Acceptance test

Design-planning

Planningof imple-

mentation,integration

and Test

Problem analysis

Realization

Planning

one turn = one phase


Evolutionary software development as a special case of the spiral model

Pagel, Six p.73

Risk analysis

sales forecast GUI-prototype

Acceptance test

R e v i e wProject plan

Validation of theprototype

revisedprojectplan

Installation

Validation of the prototype

Prototype 1Prototype n

Usable product

Planningof the second

prototype

Planningof the first

prototype

Operation andmaintenance

Problem analysis

Realization

Planning

one turn = one prototype