Object-Oriented Software EngineeringPractical Software Development using UML and Java

Chapter 1: Software and Software Engineering

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1.1 The Nature of Software...

Software is intangible• Hard to understand (or even explain) the development

effort requiredSoftware is easy to reproduce• Cost is in its development

— in some other engineering products manufacturing is the costly stage

Software industry is labor-intensive• Hard to automate

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The Nature of Software ...

Untrained people can hack something together• Quality problems are hard to determine

Software is easy to modify• People make changes without fully understanding their

effectsSoftware does not ‘wear out’• It deteriorates by having its design changed:

—erroneously, or—in ways that were not anticipated

The Nature of Software

Conclusions• Demand for software is high and rising• Producing quality software is a challenge• We have to ‘engineer’ software, not just hack something

together

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Types of Software...

Custom• For a specific customer

Generic• Sold on open market• Often called

—COTS (Commercial Off The Shelf)—Shrink-wrapped

Embedded• Built into hardware• Harder to modify

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Types of Software

Real time software• Control and monitoring systems• Must react immediately• Performance and Safety are major concerns

Data processing software• Used to run businesses• Correctness and Security of data are major concerns

Some software has both aspects

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1.2 What is Software Engineering?...

The process of solving customers’ problems by the systematic development and evolution of large, high-quality software systems within cost, time, and other constraints

Other definitions:• IEEE: (1) the application of a systematic, disciplined, quantifiable approach

to the development, operation, maintenance of software; that is, the application of engineering to software. (2) The study of approaches as in (1).

• The Canadian Standards Association: The systematic activities involved in the design, implementation and testing of software to optimize its production and support.

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What is Software Engineering?…

Solving customers’ problems• This is the goal of software engineering• Sometimes the solution is to assemble from existing

components, not build from scratch• Sometimes the solution is to buy, not assemble or build• Adding unnecessary features does not help solve

problems• Software engineers must communicate effectively to

identify and understand problems

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What is Software Engineering?…

Systematic development and evolution• An engineering process involves applying well-

understood techniques in an organized and disciplined way

• Many well-accepted practices have been formally standardized

• Most development work is evolutionary

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What is Software Engineering?…

Large, high-quality software systems• Software engineering techniques are needed because large

systems cannot be completely understood and developed by one person (within time constraints)

• Teamwork and coordination are required• Key challenge: Dividing up the work and ensuring that the

parts of the system will work properly together• The end-product must be of high quality

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What is Software Engineering?

Cost, time, and other constraints• Finite resources• Usually a deadline• The benefits must outweigh the cost

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1.3 Software Engineering and the Engineering Profession

The term Software Engineering was coined in 1968• People began to suggest that the principles of

engineering should be applied to software development

Engineering is a licensed profession• In order to protect the public• Engineers design artifacts following well-accepted

practices which involve the application of science, mathematics, economics, ….

• Ethical practice is also a key tenet of the profession

In most countries, software engineering does not (yet) require an engineering exam or license

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Software Engineering and the Engineering Profession

Ethics in Software Engineering:

Ethics refers to the concern that humans have for figuring out how best to live

Like medical, legal and business ethics, engineering ethics is a well-developed area of professional ethics

Professional engineers today are expected to both learn about and live up to ethical standards as a condition of their membership in the profession

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Software Engineering and the Engineering Profession

Ethics in Software Engineering:

Software engineering is a relatively young practice and, compared with other engineering disciplines, its culture of professionalism is still developing

Software Engineering Code of Ethics and Professional Practice (Version 5.2) as recommended by the ACM/IEEE-CS Joint Task Force is the standard for teaching and practicing software engineering

Software engineers shall adhere to these eight principles…

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Software Engineering and the Engineering Profession

Ethics in Software Engineering:

Software engineers shall1. Act consistently with public interest2. Act in the best interests of their clients3. Develop and maintain systems using the highest

standards possible4. Maintain integrity and independence5. Promote an ethical approach in management6. Advance the integrity and reputation of the profession7. Be fair and supportive to colleagues8. Participate in lifelong learning

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1.4 Stakeholders in Software Engineering

1. Users• Those who use the software

2. Customers (Project Owners)• Those who pay for the software

3. Software Developers (Software Engineers)• Those who create and maintain the software

4. Development Managers (Project Coordinators)• Those who supervise the software development process

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1.5 Software Quality...

Availability • Concerned with system failure and its associated

consequencesModifiability• The cost of change

Performance • How long it takes the system to respond when

an event occursScalability• Can the software handle larger volumes of data?

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1.5 Software Quality...

Security • Ability to resist unauthorized usage while still

providing its services to legitimate usersTestability • Ease with which software can be made to

demonstrate its faults through testingUsability • How easy it is for the user to accomplish a

desired task and the kind of user support that the product provides

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1.5 Software Quality...

Efficiency• It doesn’t waste resources such as CPU time and

memoryReliability• It does what it is required to do without failing

Maintainability• It can be easily maintained (modified, updated)

Reusability• Its parts can be used in other projects

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Software Quality and the Stakeholders

QUALITY SOFTWARE

Developer: easy to design; easy to maintain;

easy to reuse its parts

User: easy to learn; efficient to use; helps get work done

Customer: solves problems at an acceptable cost in terms of money paid and resources used

Development manager: sells more and pleases customers while costing less to develop and maintain

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Software Quality: Conflicts and Objectives

Some software qualities can conflict• Increasing efficiency can affect maintainability and/or

reusability• Increasing usability can affect efficiency• Increasing security can affect performance

Setting objectives for quality is a key engineering activity• You then design to meet the objectives

Optimizing is always necessary• for example, obtain the highest possible reliability using

a fixed budget

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Internal Quality Criteria

• Characterize aspects of the design of the software

• Have an effect on the external quality attributes• e.g.

—The amount of commenting of the code —The complexity of the code —The use of well-understood software patterns

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Short Term Vs. Long Term Quality

Short term:• Does the software meet the customer’s immediate needs? • Is it sufficiently efficient for the volume of data we have

today?Long term:• Maintainability• Customer’s future needs• Scalability

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1.6 Software Engineering Projects

Most projects are evolutionary or maintenance projects, involving work on legacy systems• Corrective projects: fixing defects• Adaptive projects: changing the product in response to

changes in—The system in which it operates—Available information—Organizational changes

• Enhancement projects: adding new features for users• Reengineering or perfective projects: changing the

system internally so that it is more maintainable

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Software Engineering Projects

Greenfield Project•‘From scratch’ project, new development•Lacks any constraints imposed by prior work•Analogy is to construction on greenfield land where there is no need to remodel or demolish an existing structure•Minority of projects

Brownfield Project •Development and deployment of a software system that must work with existing software systems•New system must take into account and coexist with already-existing software

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1.7 Activities Common to Software Projects...

Requirements• Includes

—Domain analysis—Defining the problem—Requirements gathering

- Obtaining input from as many sources as possible—Requirements analysis

- Organizing this information

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Activities Common to Software Projects...

Design• Deciding how the requirements should be implemented

using the available technology• Includes:

—Systems engineering: Deciding what should be in hardware and what in software

—Software architecture: Includes dividing the system into subsystems and deciding how the subsystems will interact

—Detailed design of the internals of a subsystem—User interface design—Design of databases

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Activities Common to Software Projects

Modeling• Creating representations of the domain and the software

— User stories— Use cases

ProgrammingQuality assurance• Reviews and inspections• Testing

DeploymentManaging the process