software engineerig- introduction

8/14/2019 Software Engineerig- Introduction

1/58


2/58

2

OutlineNature of software projectsEngineering approaches

Software processA process step

Characteristics of a good process

Waterfall model for development

Other models

Project planning


3/58

3

Software SystemsUbiquitous, used in variety ofapplications

Business, engineering, scientificapplications

Simple to complex, internal to public,single function to enterprise-wide, one

location to distributed, batch or real-time, informational to mission-critical,.


4/58

4

Challenge in large projectsDeveloping large/complex softwareapplication is very challenging

Effort intensive

High cost

Long development time

Changing needs for users

High risk of failure, user acceptance,performance, maintainability,

Quite different from one-timeprograms where author and user are

same !


5/58

5

Successful software systemSoftware development projects havenot always been successful

When do we consider a softwareapplication successful? Development completed

It is useful

It is usable, and It is used

Cost-effectiveness, maintainabilityimplied


6/58

6

Reasons for failureSchedule slippage

Cost over-runs

Does not solve users problemPoor quality of software

Poor maintainability


7/587

Reasons for failure .Ad hoc software development resultsin such problems

No planning of development work (e.g.no milestones defined)

Deliverables to user not identified

Poor understanding of user

requirements No control or review

Technical incompetence of developers

Poor understanding of cost and effort by

both developer and user


8/588

Engineering: other disciplinesLarge projects common andsuccessfully done

Buildings bridges, dams Power plants

Aircrafts, missiles,

engineering a solution:

To design, develop (build, fabricate) anartifact that meets specificationsefficiently, cost-effectively and ensuringquality

Using scientific principles.


9/589

Engineering Requires well-defined approach :repeatable, predictable

Large projects requires managing theproject itself

Manage people, money (cost),equipment, schedule

Scale makes big difference: compare

building a hut, 2storeyed house, or 50-storeyed apartment building

Quality extremely important : relatesto failures, efficiency, usability, .

People willing to pay for quality !


10/5810

Large Projects

Involve different types of people Large building : architect, civil engineer,

electrical engineer, workers (masons,carpenters), .

Continuous supervision for qualityassurance

On site supervisors (check cement/steelquality, ensuring proper mix of sand &cement, .)


11/5811

Large projects Many deliverables : architecture plan,model, structure diagrams, electricalcabling layouts,

Standards, regulations, conventionsneed to be followed

Steps, milestones defined and reviews

are carried out; progress is visibleProject planning and projectmanagement essential


12/5812

Software projects

Software is different from otherproducts

Cost of production concentrated indevelopment

Maintenance consists of makingcorrections and enhancing or adding

functions

Progress in development is difficult tomeasure


13/58

13

Apply Engineering ApproachHence planning and control even moreimportant in software development engineering approach:

Attempt to estimate cost/effort

Plan and schedule work

Involve user in defining requirements

Identify stages in development

Define clear milestones so that progress can be

measured Schedule reviews both for control and quality

Define deliverables

Plan extensive testing


14/58

14

Job of Software Developer is

difficultDealing with users

Ill-defined requirements

Concern with ease-of-use and response time

Dealing with technical people

Concerned with coding, databases, filestructures, etc.

Dealing with management

Concerned with return on their investment

Cost-benefit analysis

Schedule


15/58

15

Software ProcessProcess consists of activities/steps tobe carried out in a particular order

Software process deals with bothtechnical and management issues

Consists of different types of process

Process for software development:

produces software as end-result multiple such processes may exist

a project follows a particular process


16/58

16

Process Types Process for managing the project

defines project planning and control

effort estimations made and scheduleprepared

resources are provided

feedback taken for quality assurance

monitoring done.


17/58

17

Process Types Process for change and configurationmgmt.

Resolving requests for changes

Defining versions, their compositions Release control

Process for managing the aboveprocesses themselves

Improving the processes based on newtechniques, tools, etc.

Standardizations and certifications (ISO,CMM)


18/58

18

Multiple processes A large software development

company may have multipledevelopment processesA. For client-server based conventional

applications (sales processing, payroll)

B. For enterprise-level (ERP) projects based onpackages and customization

C. For web-based e-commerce typeD. For data-warehousing/decision-support type

The company may have manyprojects in each category


19/58

19

Step in a ProcessEach step has a well-definedobjective

Requires people with specific skillsTakes specific inputs and produceswell-defined outputs

Step defines when it may begin

(entry criteria) and when it ends (exitcriteria)

Uses specific techniques, tools,

guidelines, conventions.


20/58

20

Process step

Step must be executed as per project planthat gives duration, effort, resources,constraints, etc.

It must produce information formanagement so that corrective actionscan be taken

E.g., adding more resources

A step ends in a review (V&V) Verification: check consistency of outputs

with inputs (of the step)

Validation: check consistency with user needs


21/58


22/58


23/58

23

A Good Process

Predictable for quality: with respect to number andtype of defects, performance,

Predictable process is said to be understatistical control , where actual values are

close to expected values

It supports testing and maintainability

Maintenance by third party

Follow standards, provide necessary documentation

This characteristic differentiates between prototypeand product


24/58


25/58

25

Waterfall Model for

DevelopmentHere, steps (phases) are arranged inlinear order

A step take inputs from previous step,

gives output to next step (if any) Exit criteria of a step must match with

entry criteria of the succeeding step

It follows specify, design, build

sequence that is intuitively obviousand appears natural


26/58

26

Waterfall Model

Produces many intermediatedeliverables, usually documents

Standard formats defined

Act as baseline used as reference (forcontractual obligations, formaintenance)

Important for quality assurance, project

management, etc.

It is widely used (with minorvariations) when requirements are

well understood


27/58

27

Waterfall Modelsystem

engineering

AnalysisProject planning

design

code

testing &integration

Installation &

maintenance

-software part of some larger system-establish requirements for all elements of the system; assign some

to software

-understand information domain, functions, performance

and interfacing. Project plans made

-translate requirements into s/w architecture, data structures

and procedural details. A detailed design step can be

added

-programming

-test logic and function interfaces

-deployment; make changes for

-Errors, performance-changes in requirement


28/58

28

Deliverables in Waterfall

ModelProject plan and feasibility reportRequirements document (SRS :Software Requirement Specifications)

System design documentDetailed design document

Test plans and test reports

Source codeSoftware manuals (user manual,installation manual)

Review reports


29/58

29

Cost/Effort Distribution

Accumulated cost increases dramatically asprogrammers, operators, technical writers andcomputer time is committed.

Cost of discovering and fixing errors also increases with

steps

Problemdefinitio

n

Feasibility study

Analysis Systemdesign

Detaileddesign

Implemen-

tation

Mainten-

ance

Total accumulatedcost


30/58

30

Shortcomings of Waterfall

ModelRequirements may not be clearlyknown, especially for applications nothaving existing (manual) counterpart

Railway reservation: manual systemexistes, so SRS can be defined

On-line container management for

railways - new Knowledge management for a central

bank new


31/58

31

Shortcomings Requirements change with timeduring project life cycle itself

Users may find solution of little use

Better to develop in parts in smallerincrements; this is common forpackages, system software

Considered documentation-heavy: so

much documentation may not berequired for all types of projects.


32/58

32

Prototyping Model

When customer or developer is notsure

Of requirements (inputs, outputs)

Of algorithms, efficiency, human-machineinteraction

A throwaway prototype built from

currently known user needsWorking or even paper prototype


33/58

33

Prototyping

Quick design focuses on aspectsvisible to user; features clearly

understood need not be implementedPrototype is tuned to satisfy customerneeds

Many iterations may be required toincorporate changes and newrequirements

Final product follows usual define-design-build-test life cycle


34/58

34

Prototyping

Requirementsgathering

Quick

design buildprototype

evaluate &refine

Engineerproduct


35/58


36/58

36

Iterative Development

Useful for product development wheredevelopers define scope, features toserve many customers

Early version with limited featureimportant to establish market and getcustomer feedback

Initial version may follow any method

A list of features for future versionsmaintained

Each version is analyzed to decide

feature list for next iteration


37/58

37

Evolutionary Development model [SE-7, Fig4.2]

ValidationFinalversion

DevelopmentIntermediate

versions

Specification Initialversion

Outline

description

Concurr ent

activities


38/58

38

Evolutionary Development.. Main characteristics:

The phases of the software construction areinterleaved

Feedback from the user is used throughout theentire process

The software product is refined through manyversions

Types of evolutionary development: Exploratory development

Throw-away prototyping


39/58

39

Evolutionary Development Advantages:

Deals constantly with changes

Provides quickly an initial version of the system

Involves all development teams

Disadvantages:

Quick fixes may be involved

Invisible process, not well-supported bydocumentation

The systems structure can be corrupted bycontinuous change


40/58

40

Evolutionary Development

Disadvantages [contd]: Special tools and techniques may be

necessary

The client may have the impression the firstversion is very close to the final product andthus be less patient

Applicability: When requirements are not well understood

When the client and the developer agree ona rapid prototype that will be thrown away

Good for small and medium-sized softwaresystems


41/58

41

Component-based Software

Engineering

Requirementsspecification Componentanalysis

Developmentandintegration

Systemdesignwithreuse

Requirementsmodification

Systemvalidation


42/58

42


Engineering..

Main characteristics:

Makes intensive use of existing reusable

componentsThe focus is on integrating the

components rather than on creatingthem from the scratch


43/58


44/58

44


Engineering Disadvantages:

Compromises in requirements are needed

Less control over the systems evolution

Applicability:

When there is a pool of existingcomponents that could satisfy therequirements of the new product

Emerging trend: integration of webservices from a range of suppliers


45/58

45

Spiral ModelActivities are organized in a spiral having

many cycles

Four quadrants in each cycle

1. Determine objectives,Alternatives, constraints

2. Evaluate alternatives,identify and handle risks

4. Plan next step 3. Develop the software


46/58


47/58

47

The Spiral Model


48/58

48

Spiral Model

Main characteristics:

Also a hybrid model that support processiteration

The process is represented as a spiral, eachloop in the spiral representing a process phase

Four sectors per loop: objective setting, riskassessment and reduction, development and

validation, planning Risk is explicitly taken into consideration


49/58

49

Spiral Model Advantages:

Risk reduction mechanisms are in place

Supports iteration and reflects real-world practices

Systematic approach

Disadvantages: Requires expertise in risk evaluation and reduction

Complex, relatively difficult to follow strictly

Applicable only to large systems

Applicability: Internal development of large systems


50/58

50

The Rational Unified Process

P h as e i te rat i o n

In cep t i o n E l ab o ra t i o n C o n s t ru c t i o n Tran s i t i o n


51/58

51

Major work products in UP phases

Inception phase Vision doc, early use cases, feasibility, project

plans

Elaboration phase

Detailed use cases, analysis, architecturedesign, detailed plan, preliminary user manual

Construction phase Detailed design, components, test plans/cases,

implementation, detailed manuals

Transition phase Delivery, beta/acceptance, user feedback


52/58

52

What is CASE (Computer-Aided

Software Engineering)

Software systems that are intended toprovide automated support for softwareprocess activities.

CASE systems are often used for methodsupport.

Upper-CASE Tools to support the early process activities of

requirements and design;

Lower-CASE Tools to support later activities such as

programming, debugging and testing.


53/58

53

Classification of CASE technology [SE-7, Fig 4.14]

Single-methodworkbenches

General-purposeworkbenches

Multi-methodworkbenches

Language-specificworkbenches

Programming TestingAnalysis anddesign

Integratedenvironments

Process-centredenvironments

Filecomparators

CompilersEditors

EnvironmentsWorkbenchesTools

CASEtechnology


54/58

54

Project Management Process

Runs in parallel to development process

Project planning, monitoring and controlare the basic goals

Project plan indicates how project will beexecuted successfully

Without plan, there is no management

Without measurement, not much planningpossible

Plan allows progress to be measured

Plan produced before development beginsand constantly updated


55/58


56/58

56

Project Monitoring and

ControlPlan defines various activities: manyways to represent: Gantt chart, time

bar chart, PERT/CPM project activitynetwork

Show activities, expected durations,resources allocated

Critical paths can be identified


57/58

57

Project monitoring

Each development step givesinformation for tracking progress for

identifying delays, bottlenecks, etc. Allows corrective action: add more

resources reduce scope, re-negotiatecost/schedule, etc.


58/58

SummaryChallenges in software development andneed for engineering approach

Step-by-step methodology with specificdeliverables

Types of software processes For development, for project management,

Precise definition of a step

Waterfall model : natural, widely followed

in spite of its limitationsProject management for planning,monitoring and control

software engineerig- introduction

Documents