SOFTWARE PROCESSES

MUHAMMAD RIZWAN

Fall 2012

Objectives

To introduce software process models To describe three generic process

models and when they may be used To describe outline of process models for

requirements engineering, software development, testing and evolution

To explain the Rational Unified Process model

To introduce CASE technology to support software process activities

Topics covered

Software process models Process iteration Process activities The Rational Unified Process Computer-aided software engineering

(CASE)

4

Software Engineering

0

10

20

30

40

50

60

70

Analys

is

Specif

icatio

n

Design

Imple

men

tatio

n

Test

ing

Software Life Cycle PhaseE

ffo

rt Without SE

Applying SE

The phases of a software development cycle.

    Analysis:

   Specification

   Design

   Implementation

   Testing

   Delivery/Maintenance

Software Life Cycle

5

Feasibility study – WHY? Cost benefit analysis (is it worth doing the project)

Requirements analysis + specification: WHAT? What should the software do, produce a document.

Design - How? How should the software do it. Architectural design (overall structures + organization of objects/modules, choice of data structures, etc.

Coding/Implementation: Realize ! components. Code modules, products: software,

Testing: Realize ! Test individual modules, test whether several modules work together, test system as a whole, document test results.

Deliver and maintenance : Evolve!

Software Life Cycle

6

Good Engineering Practice (Analysis - The Starting Point)

A Legacy System: Does not provide any longer state-of the art technology, lack of functionality and user friendliness

Good Engineering Practice(More Analysis)

What are the customer expectations? Frequently these might be unrealistic and not functional (see the wheels)

7

Good Engineering Practice (Specifications)

Based on the analysis a more realistic and functional product is specified. First specification drawings are created.

8

9

Good Engineering Practice(Detailed Specifications)

Interior and exterior are specified in more detail

Good Engineering Practice(Design)

First 1: 4 design models are created

10

11

Good Engineering Practice(More Design)

First 1:1 models are created, leading to a more realistic design of the new car.

12

Good Engineering Practice(More Design and first Testing)

Prototypes are tested, re-designed and re-tested if necessary

13

Good Engineering Practice(Implementation)

Product is product and final tests are conducted before product is shipped

Good Engineering Practice(Final Product)

The final product is introduced: Meeting the customer requirements with respect to design and functionality.

14

15

Good Engineering Practice(Maintenance)

The maintenance process for the new models are introduced:

Layered View of SE Layered approach:

Process. Methods. Tools.

Software EngineeringSoftware Engineering

a “quality” focusa “quality” focus

process modelprocess model

methodsmethods

toolstools

The software process

A structured set of activities required to develop a software system Specification – defining what the system should do; Design and implementation – defining the organization of

the system and implementing the system; Validation – checking that it does what the customer

wants; Evolution – changing the system in response to changing

customer needs. A software process model is an abstract

representation of a process. It presents a description of a process from some particular perspective.

Software Process Models

A software process model is a standardised format for

planning organising, and runninga new development project.

18

Planning with Models

SE projects usually live with a fixed financial

budget. (An exception is maintainance?)

Additionally, time-to-market places a strongtime constraint.

There will be other project constraints such

as staff.

19

Project constraints

money

timeComputing resources

Examples of Project Constraints

20

staff

programmers managersdesigners

Planning with Process Models

Project planning is the art of scheduling the necessary activities, in time, space and across staff in order to optimise:

project risk [low] (see later) profit [high] customer satisfaction [high] worker satisfaction [high] long-term company goals

21

Generic software process models

The waterfall model Separate and distinct phases of specification and

development. Incremental development

Specification, development and validation are interleaved. May be plan-driven or agile

Reuse-oriented software engineering The system is assembled from existing components.

May be plan-driven or agile.

The Waterfall Model23

Advantages

1. Easy to understand and implement.2. Widely used and known (in theory!)3. Reinforces good habits: define-before-

design, design-before-code4. Identifies deliverables and milestones5. Document driven, URD, SRD, … etc.

Published documentation standards, e.g. PSS-05.

6. Works well on mature products and weak teams.

24

Disadvantages I

1. Idealised, doesn’t match reality well.2. Doesn’t reflect iterative nature of

exploratory development.3. Unrealistic to expect accurate

requirements so early in project4. Software is delivered late in project,

delays discovery of serious errors.

25

Disadvantages II

5. Difficult to integrate risk management6. Difficult and expensive to make

changes to documents, ”swimming upstream”.

7. Significant administrative overhead, costly for small teams and projects.

26

Incremental development

Objective is to work with customers and to evolve a final system from an initial outline specification. Should start with well-understood requirements and add new features as proposed by the customer.(Create different versions) Reduce cost Easy to get customer feedback Rapid delivery & deployment of software

Throw-away prototyping Objective is to understand the system

requirements. Should start with poorly understood requirements to clarify what is really needed.

28

Chapter 2 Software Processes

Concurrentactivities

ValidationFinal

version

DevelopmentIntermediate

versions

SpecificationInitial

version

Outlinedescription

Incremental development

Problems Lack of process visibility; 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.

Incremental development

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

Process stages Component analysis; Requirements modification; System design with reuse; Development and integration.

This approach is becoming increasingly used as component standards have emerged. e.g. using databases, spread sheets, word

proccessors, graphics software, web browsers, etc.

Reuse-oriented development

Reuse-oriented development

Requirementsspecification

Componentanalysis

Developmentand integration

System designwith reuse

Requirementsmodification

Systemvalidation

Advantages Fast, cheap solution May give all the basic functionality Well defined project, easy to runDisadvantages Limited functionality Licensing problems, freeware,

shareware, etc. License fees, maintainance fees,

upgradecompatibility problems

Reuse-oriented development

Spiral Model

Since end-user requirements are hard to obtain/define, it is natural to develop software in an experimental way: e.g.

1. Build some software2. See if it meets customer

requirements3. If no goto 1 else stop.

Boehm’s spiral model

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

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

No fixed phases such as specification or design - loops in the spiral are chosen depending on what is required.

Risks are explicitly assessed and resolved throughout the process.

34

Chapter 2 Software Processes

Boehm’s spiral model of the software process

35

Chapter 2 Software Processes

Spiral model sectors

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

A development model for the system is chosen which can be any of the generic models.

Planning The project is reviewed and the next phase of the

spiral is planned.

Spiral Model Discussion

Pros1. Realism: the model accurately reflects the

iterative nature of software development on projects with unclear requirements

2. Comprehensive model decreases risk

3. Good project visibility.

Cons1. Needs technical expertise in risk analysis to really

work2. Model is poorly understood by non-technical

management, hence not so widely used3. Complicated model, needs competent professional

management. High administrative overhead.

37

Process activities

Software specification Software design and implementation Software validation Software evolution They are organized differently in different development

processes. In the waterfall model, they are organized in sequence, whereas in incremental development they are inter-leaved.

38

Chapter 2 Software Processes

Software specification

The process of establishing what services are required and the constraints of the system’s operation and development.

Requirements engineering process Feasibility study

Is it technically and financially feasible to build the system? Requirements elicitation and analysis

What do the system stakeholders require or expect from the system?

Requirements specification Defining the requirements in detail

Requirements validation Checking the validity of the requirements

39

Chapter 2 Software Processes

The requirements engineering process

Feasibilitystudy

Requirementselicitation and

analysisRequirementsspecification

Requirementsvalidation

Feasibilityreport

Systemmodels

User and systemrequirements

Requirementsdocument

Software design and implementation

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

Software design Design a software structure that realises the

specification; Implementation

Translate this structure into an executable program;

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

41

Chapter 2 Software Processes

Design process activities

Architectural design, where you identify the overall structure of the system, the principal components (sometimes called sub-systems or modules), their relationships and how they are distributed.

Interface design, where you define the interfaces between system components.

Component design, where you take each system component and design how it will operate.

Database design, where you design the system data structures and how these are to be represented in a database.

42

Chapter 2 Software Processes

The software design process

Architecturaldesign

Abstractspecification

Interfacedesign

Componentdesign

Datastructuredesign

Algorithmdesign

Systemarchitecture

Softwarespecification

Interfacespecification

Componentspecification

Datastructure

specification

Algorithmspecification

Requirementsspecification

Design activities

Design products

Structured methods

Systematic approaches to developing a software design.

The design is usually documented as a set of graphical models.

Possible models Sequence model; (Use Case) State transition model; (Submit, Assign) Structural model; Data-flow model.

Programming and debugging Translating a design into a program and

removing errors from that program. Programming is a personal activity -

there is no generic programming process.

Programmers carry out some program testing to discover faults in the program and remove these faults in the debugging process.

The debugging process

Locateerror

Designerror repair

Repairerror

Re-testprogram

Software validation

Verification and validation (V & V) is intended to show that a system conforms to its specification and meets the requirements of the customer.

Involves checking and review processes and system testing.

System testing involves executing the system with test cases that are derived from the specification of the real data to be processed by the system.

Testing is the most commonly used V & V activity.

47

Chapter 2 Software Processes

The testing process

Componenttesting

Systemtesting

Acceptancetesting

Testing stages

Component or unit testing Individual components are tested

independently; Components may be functions or objects or

coherent groupings of these entities. System testing

Testing of the system as a whole. Testing of emergent properties is particularly important.

Acceptance testing Testing with customer data to check that the

system meets the customer’s needs.

Testing phases

Requirementsspecification

Systemspecification

Systemdesign

Detaileddesign

Module andunit codeand test

Sub-systemintegrationtest plan

Systemintegrationtest plan

Acceptancetest plan

ServiceAcceptance

testSystem

integration testSub-system

integration test

Software evolution

Software is inherently flexible and can change.

As requirements change through changing business circumstances, the software that supports the business must also evolve and change.

Although there has been a limit between development and evolution (maintenance) this is increasingly irrelevant as fewer and fewer systems are completely new.

System evolution

Assess existingsystems

Define systemrequirements

Propose systemchanges

Modifysystems

Newsystem

Existingsystems

Key points

Software processes are the activities involved in producing a software system. Software process models are abstract representations of these processes.

General process models describe the organization of software processes. Examples of these general models include the ‘waterfall’ model, incremental development, and reuse-oriented development.

53

Chapter 2 Software Processes

Key points

Requirements engineering is the process of developing a software specification.

Design and implementation processes are concerned with transforming a requirements specification into an executable software system.

Software validation is the process of checking that the system conforms to its specification and that it meets the real needs of the users of the system.

Software evolution takes place when you change existing software systems to meet new requirements. The software must evolve to remain useful.

54

Chapter 2 Software Processes

The Rational Unified Process A modern process model derived from

the work on the UML and associated process.

Normally described from 3 perspectives A dynamic perspective that shows phases

over time; A static perspective that shows process

activities; A practice perspective that suggests good

practice.

RUP phase model

Phase iteration

Inception Elaboration Construction Transition

RUP phases

Inception Establish the business case for the system.

Elaboration Develop and 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 practice

Develop software iteratively Manage requirements Use component-based architectures Visually model software Verify software quality Control changes to software

Computer-aided software engineering

Computer-aided software engineering (CASE) is software to support software development and evolution 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; Automated translators to generate new versions of a

program.

Case technology

Case technology has led to significant improvements in the software process. However, these are not the order of magnitude improvements 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 interactions. CASE technology does not really support these.

CASE classification

Classification helps us understand the different types of CASE tools and their support for process activities.

Functional perspective Tools are classified according to their specific

function. Process perspective

Tools are classified according to process activities that are supported.

Integration perspective Tools are classified according to their organisation

into integrated units.

Functional tool classificationTool type Examples

Planning tools PERT tools, estimation tools, spreadsheets

Editing tools Text editors, diagram editors, word processors

Change management tools Requirements traceability tools, change control systems

Configuration management tools Version management systems, system building tools

Prototyping tools Very high-level languages, user interface generators

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

Language-processing tools Compilers, interpreters

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

Testing tools Test data generators, file comparators

Debugging tools Interactive debugging systems

Documentation tools Page layout programs, image editors

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

Activity-based tool classification

Specification Design Implementation Verificationand

Validation

Re-engineering tools

Testing tools

Debugging tools

Program analysis tools

Language-processingtools

Method support tools

Prototyping tools

Configurationmanagement tools

Change management tools

Documentation tools

Editing tools

Planning tools

Tools, workbenches, environments

Single-methodworkbenches

General-purposeworkbenches

Multi-methodworkbenches

Language-specificworkbenches

Programming TestingAnalysis and

design

Integratedenvironments

Process-centredenvironments

Filecomparators

CompilersEditors

EnvironmentsWorkbenchesTools

CASEtechnology

Key points

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

Software process models are abstract representations of these processes.

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

Generic process models describe the organisation of software processes. Examples include the waterfall model, evolutionary development and component-based software engineering.

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

Key points

Requirements engineering is the process of developing a software specification.

Design and implementation processes transform the specification to an executable program.

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

Evolution is concerned with modifying the system after it is in use.

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

CASE technology supports software process activities.