Software Engineering Lec 2

Bernd Bruegge & Allen H. Dutoit Object-Oriented Software Engineering: Using UML, Patterns, and Java 1
Software Process

Introduction
 How Microsoft Builds Software?
 Microsoft has probably tackled more PC software projects than
any other company in the industry.
 The complexity of some of its products, such as Windows 95
(which contains more than 11 million lines of code and
required a development team of more than 200 programmers
and testers),
 They simply use software engineering techniques through the
software process.

Software Process
Fundamental Assumption:
Good processes lead to good software
Good processes reduce risk
Good processes enhance visibility

Basic Process Steps in all Software Development
• Feasibility and planning
• Requirements
• System and program design
• Implementation and testing
• Acceptance testing and release
• Operation and maintenance
It is essential to distinguish among these process steps and
to be clear which you are are doing at any given moment.
Do not confuse requirements and design

Sequence of Processes (software lifecycle)
Every software project will include these basic processes, in some
shape or form, but they may be carried out in various sequences
Major alternatives
• Sequential: Complete each process step before beginning the
next (but see the next few slides). Waterfall model.
• Iterative: Go quickly through all process steps to create a
rough system, then repeat them to improve the system. Iterative
refinement.

Sequential Development:
The Waterfall Model
Requirements
System design
Testing
Operation & maintenance
Program design
Implementation (coding)
Acceptance & release
Requirements
Design
Implementation
Feasibility study

Discussion of the Waterfall Model
Advantages:
• Process visibility
• Separation of tasks
• Quality control at each step
• Cost monitoring at each step
Disadvantages:
Each stage in the process reveals new
understanding of the previous stages, that often
requires the earlier stages to be revised.
The Waterfall Model is not enough!

Sequence of Processes
A pure sequential model is impossible
Examples:
• A feasibility study cannot create a proposed budget and
schedule without a preliminary study of the requirements and a
tentative design.
• Detailed design or implementation usually reveals gaps in the
requirements specification.
The plan must allow for some form of iteration.

Modified Waterfall Model-1
Requirements
System design
Testing
Operation & maintenance
Program design
Implementation (coding)
Acceptance & release
Waterfall model
with feedback
This is better
Feasibility study

Modified Waterfall Model-2
Feasibility study
Test
Software
Requirements Test
System design
Design Test
Program design
Design Test
Implementation
Test
Experimentation
Debugging Test
Acceptance
Maintenance Test

Iterative/spiral Refinement
Concept: Initial implementation for client and user
comment, followed by refinement until system is complete
Requirements
DesignImplementation
Evaluation

The Spiral Process
tim
1
Requirements
analysis
Design
Implementation
Evaluation
1Iteration #
1
1
2
2
2
3
3
3
Product released X
M I L E S T O N E S
2 3
2 31
Intermediate version
(prototype) X
Intermediate version
(2nd
prototype) X

Other Life-Cycle Models
 Build-and-fix model
 Rapid prototyping model
 Incremental model
 Extreme programming
 Component-based software engineering
 Synchronize-and-stabilize model
 Object-oriented life-cycle models

1-Build and Fix Model

Notes
 Most software is developed using build-and-fix
model. Basically there is no model.
No specifications
No design
 This model is completely unsatisfactory and should
not be adopted.

3-Incremental development advantages
 Customer value can be delivered with each increment
so system functionality is available earlier.
 Early increments act as a prototype to help elicit
requirements for later increments.
 Lower risk of overall project failure.
 The highest priority system services tend to receive
the most testing.

Incremental development

4-Extreme Programming (XP)
 One of the best-know examples of an Agile Process
 Appropriate for environments with:
 Small teams
 Rapidly-changing requirements
 Some of the principles XP is based on are:
 Small Releases - Software developed in stages that are updated frequently
 Simple Design – Implement code needed to achieve customer’s results without
emphasis on future versions
 Testing – Done throughout the whole development process. Tests are design
first, before writing the software

Component-based software engineering
 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.

Reuse-oriented development

Computer-Aided Software Engineering (CASE)
 Computer-Aided Software Engineering (CASE) is software to support
software development and evolution processes.
 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 classification
Tool 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 datagenerators, 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 Verification
and
Validation
Re-eng ineering tools
Testing tools
Debugging tools
Programanalysis tools
Language-processing
tools
Method suppor t tools
Prototyping tools
Configuration
management tools
Change management tools
Documentation tools
Editing tools
Planning tools

End of Slides

Software Engineering Lec 2

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Software Engineering Lec 2