1. Software Life Cycle “What happens in the ‘life’ of software”
TCS2411 Software Engineering

2. TCS2411 Software Engineering
Lecture Objectives
To look at the ‘life cycle’ of a software
To understand the software process and its related elements
To relate to the different software engineering paradigms
TCS2411 Software Engineering

3. Software Engineering Layers
a “quality” focus
process model
methods
tools
TCS2411 Software Engineering

4. TCS2411 Software Engineering
Software Process
Activities in software projects
Characterised by a common process framework
Framework activities - task sets
Umbrella activities
“Process maturity” enables development of quality software products
TCS2411 Software Engineering

5. Common Process Framework
Framework activities
work tasks
work products
milestones & deliverables
QA checkpoints
Umbrella Activities
TCS2411 Software Engineering

6. TCS2411 Software Engineering
Umbrella Activities
Software project management
Formal technical reviews
Software quality assurance
Software configuration management
Document preparation and production
Reusability management
Measurement
Risk management
TCS2411 Software Engineering

7. Process as Problem Solving
TCS2411 Software Engineering

8. The Process Model: Adaptability
the framework activities will always be applied on every project ... BUT
the tasks (and degree of rigor) for each activity will vary based on:
the type of project (an “entry point” to the model)
characteristics of the project
common sense judgment; concurrence of the project team
TCS2411 Software Engineering

9. The Primary Goal: High Quality
Remember:
High quality = project timeliness
Why?
Less rework!
TCS2411 Software Engineering

10. The Systematic Process
Problem
Analysis
Design
Models
Development
Solution
Testing
TCS2411 Software Engineering

11. TCS2411 Software Engineering
Generic Phases
Definition Phase
Focus on ‘what’ the software is
Development Phase
Focus on ‘how’ the software works
Maintenance Phase
Focus on ‘change’ to the software
TCS2411 Software Engineering

12. TCS2411 Software Engineering
Definition Phase
Identify information to be processed
Identify system behaviour - functions and performance
Determine constraints, interfaces, validation criteria
Major tasks:
System engineering
Software project planning
Requirements analysis
TCS2411 Software Engineering

13. TCS2411 Software Engineering
Development Phase
Define data structures, function implementation, procedural details, interfaces
Translate design to programming language
How testing is performed
Major tasks:
Software design
Code generation
Software testing
TCS2411 Software Engineering

14. TCS2411 Software Engineering
Maintenance Phase
Reapplies definition and development phases to existing software
Types of changes:
Correction
Adaptation
Enhancement
Prevention
TCS2411 Software Engineering

15. TCS2411 Software Engineering
Waterfall Model
TCS2411 Software Engineering

16. Waterfall Model Characteristics
The classic life cycle - oldest and most widely used paradigm
Activities ‘flow’ from one phase to another
If there are corrections, return to a previous phase and ‘flow’ from there again
Major advantages: Good for planning and well-defined/repeated projects
TCS2411 Software Engineering

17. Problems of Waterfall Model
Real projects often follow the sequence
All requirements may not be stated explicitly by customer
Customer only sees the results after some time
Developers are often delayed at certain phases
TCS2411 Software Engineering

18. TCS2411 Software Engineering
Prototyping Model
Requirements
gathering and
refinement
Building
prototype
Quick
design
Customer
evaluation
Refining
Engineer
product
Start
Stop
TCS2411 Software Engineering

19. Prototyping Model Characteristics
Developer and customer determine objectives and draft requirements
Prototype quickly produced and evaluated by customer
Prototype then refined, and re-evaluated
Process iterated, before final product development
Advantages: Customer participation and better requirements
TCS2411 Software Engineering

20. Problems of Prototyping Model
Problem 1: Customer may see prototype as working model and expects fast results
Problem 2: Developer compromised when producing prototype quickly, e.g. different operating system or programming language
TCS2411 Software Engineering

21. Rapid Application Development (RAD)
Business
Modeling
Data
Process
Application
Generation
Testing &
Turnover
Team #1
Team #2
Time period
TCS2411 Software Engineering

22. TCS2411 Software Engineering
RAD Characteristics
“High-speed” version of waterfall model
Primarily for information systems applications
Requirements well-understood, fully functional system produced in short time
The application modularised - major functions can be completed in 3 months
Separate teams complete the functions, then integrated as a whole
Requires human resource and commitment
TCS2411 Software Engineering

23. TCS2411 Software Engineering
Incremental Model
TCS2411 Software Engineering

24. Incremental Model Characteristics
Software separated into different “increments” - complete working portions
Focus on delivery of operational product with each increment - can be evaluated
Useful when insufficient staff and can be planned to manage technical risks, e.g. waiting for new hardware
TCS2411 Software Engineering

25. TCS2411 Software Engineering
Spiral Model
TCS2411 Software Engineering

26. Spiral Model Characteristics
Originally proposed by Boehm, couples iterative nature of prototyping and the systematic aspects of waterfall model
Software is developed in series of incremental releases
Each iteration produces a more complete product
Better management through risk analysis
TCS2411 Software Engineering

27. Problems of Spiral Model
May be difficult to convince customers that evolution is controllable
Demands risk assessment expertise - major risk will cause problems if not identified
Relatively new and not widely used - cannot determine performance
TCS2411 Software Engineering

28. Component Assembly Model
Extract
components
yes
Identify
candidate
components
Look up
components
in library
Available?
Construct
System no
Build
components
TCS2411 Software Engineering

29. Component Assembly Characteristics
Use of object-oriented technology
Components - classes that encapsulate both data and algorithms
Components developed to be reusable
Paradigm similar to spiral model, but engineering activity involves components
System produced by assembling the correct components
TCS2411 Software Engineering

30. Fourth Generation Techniques (4GT)
TCS2411 Software Engineering

31. TCS2411 Software Engineering
4GT Characteristics
Use of software tools that allow software engineer to specify s/w characteristics at higher level
The tools generate codes based on specification
More time in design and testing - increase productivity
Tools may not be easy to use, codes generated may not be efficient
TCS2411 Software Engineering

32. TCS2411 Software Engineering
Other Process Models
Component assembly model—the process to apply when reuse is a development objective
Concurrent process model—recognizes that different part of the project will be at different places in the process
Formal methods—the process to apply when a mathematical specification is to be developed
Cleanroom software engineering—emphasizes error detection before testing
TCS2411 Software Engineering

33. TCS2411 Software Engineering
Conclusion
The paradigm used for development of software depends on a number of factors
People - staff & users
Software product
Tools available
Environment
Existing models makes development process clearer, but they can be evolved to become new paradigms
TCS2411 Software Engineering

34. TCS2411 Software Engineering
References
“Software Engineering: A Practitioner’s Approach” 5th Ed. by Roger S. Pressman, Mc-Graw-Hill, 2001
“Software Engineering” by Ian Sommerville, Addison-Wesley, 2001
TCS2411 Software Engineering