Software Engineering Methodologies

1. Importance of Software Engineering and usage

2. What’s a software?

3. Definition of Software Engineering

4. Software Engineering ethics

5. Software Engineering processes

6. Software Engineering methodologies

Contents

Most software today is very much like an Egyptian pyramid with millions of brickspiled on top of each other, with no structural integrity, but just done by brute force and thousands of slaves. Alan Kay, ACM Queue,2005

Why Software Engineering?

http://en.wikipedia.org/wiki/Alan_Kay

Software Engineering is a great achievement







Contents

• Software is a Computer programs and associated documentation defining a project.

• Good software should deliver the required functionality and performance to the user and should be maintainable, dependable, and usable

What’s software?

Good software features

Q. What are natural constrains or limits of software ?

Q. What are the consequences of the above constraints?







Contents

Software Engineering is the application of a systematic, disciplined, quantifiable approach to development, operation and maintenance of software: that is, the application of engineering to software.”

IEEE Standard Computer Dictionary

IEEE defines Software Engineering







Contents

Software engineering ethics

1.Confidentiality: You should normally respect the confidentiality of your employers or clients irrespective of whether or not a formal confidentiality agreement has been signed.

2. Competence: You should not misrepresent your level of competence. You should not knowingly accept work that is outside your competence.

3. Intellectual property rights: You should be aware of local laws governing the use of intellectual property such as patents and copyright. You should be careful to ensure that the intellectual property of employers and clients is protected.

4. Computer misuse: You should not use your technical skills to misuse other people’s computers. Computer misuse ranges from relatively trivial (game playing on an employer’s machine, say) to extremely serious (dissemination of viruses or other malware).







Contents

Software development

processes (SDLC)

Software Management

processes

Software Engineering processes are divided into

Software Process is a sequence of activities leading to production

Software engineering Processes

Software specifications

Software development

Software validation

Software evolution

Software fundamental activities(General Model)







Contents

• Waterfall Model

• Prototyping Model

• Incremental Model

• Iterative Model

• Agile

Software engineering methodologies (techniques)

Waterfall Methodology

Analysis(Requirements

Definitions)

Design(system and software

design)

Maintenance

Development and Implementation

System Testing

Waterfall Advantages

• Easy to understand & Use.

• Easy to manage

•Phases are processed and completed one at a time.

• Works well for projects where requirements are clear & stable.

Waterfall Disadvantages

• It’s hard to respond to changing customer requirements.

• Each phase output is an input to the next phase , so delay in one phase may delay the whole project.

•In practice, phases overlaps and displace achieved.

• software is produced late during the life cycle.

• Poor model for complex and requirements variant projects.

Maintenance


System Testing

prototyping

Customer evaluation

Review

Design

Prototyping Methodology

Analysis(Requirements Definitions)

Design(quick design)

Customer approval

Prototyping Advantages

• Customers can “see” the system requirements as they are

being gathered.

• Developers learn from customers .

• A more accurate end product.

• Allows for flexible design and development.

• Steady, visible signs of progress produced.

• Interaction with the prototype stimulates awareness of additional

needed functionality.

• Overall maintainability may be overlooked

• The customer may want the prototype delivered.

• Process may continue forever (scope creep)

Prototyping disadvantages

Analysis

Design

Development

Testing

Iterative Model

Product delivery and maintenance

Iterative = waterfall+ prototyping

Iterative Model

Iteration 1

Iterative Model

Iteration 2

Iterative Model

Iteration 3

Incremental Model•Divide into mini-Waterfalls

• It means you develop one part of the system and when it’s ready you develop the next part

Analysis DesignDevelopment and Implementation Testing 1st Increment

Analysis DesignDevelopment and Implementation Testing 2nd Increment

Analysis DesignDevelopment and Implementation Testing 3rd Increment

Incremental Model Analysis Design

Development and Implementation Testing 1st Increment



Incremental Model

Analysis DesignDevelopment and Implementation Testing 3rd Increment



Incremental Model

Agile Methodology

Incremental Model(Enhanced waterfall)

Iterative Model(Waterfall+protptyping)

+

Agile Model

Agile Manifesto

1. Individuals and interactions over processes and tools

2. Working software over comprehensive documentation

3. Customer collaboration over contract negotiation

4. Responding to change over following a plan

Agile Manifesto

System Testing

Agile Model

Analysis(Requirements

Definitions)

Design(system and software

design)


1. Extreme Programming (XP)

2. SCRUM

3. Crystal Family

4. Open Source

5. Adaptive Software Development (ASD)

6. Feature Driven Development (FDD)

7. Dynamic System Development Method (DSDM)

Agile

Agile suitability

Agile methods have been very successful for some types of system development:

1. Product development where a software company is developing a small or medium-sized product for sale.

2. Custom system development within an organization, where there is a clear commitment from the customer to become involved in the development process and where there are not a lot of external rules and regulations that affect the software.

Agile difficulties

1.Customer availability.

2. Individual team members personalities suitability to interact with other teams

3. Priority determination may be extremely difficult especiallyfor many stakeholders.

4. Difficulty of shifting to a new model especially for large companies

Agile and Plan-driven(water fall) methodologiesdifferences

Agile Plan-driven

Iterative and Incremental Phased

Working Software every build Working software in final phase

More Visibility- working software Less visibility ,prototypes

Changes accepted in all phases

Changes accepted at certain stages

only

Conclusion

Agile and Plan-driven methodologiessuitability

Agile Plan-driven

Short term projects Long term projects

Senior developers Junior / Senior developers

Requirements change often Requirements do not change often

Small number of developers Small/Large number of developers

Culture that responds to change Culture that demands order

Software Engineering Methodologies

Documents

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