Se Introduction

Chapter -1 Importance of Software Engineering:

Software’s Dual Role 

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Software is a product  Delivers computing potential of hardware and networks  Transforms information :Produces, manages, acquires, modifies, displays, or transmits information Software is a vehicle for delivering a product  Supports or directly provides system functionality  Controls other programs (e.g., an operating system)  Effects communications (e.g., networking software)  Helps build other software (e.g., software tools)

What is Software? Software is a set of items or objects that form a “configuration” that includes • programs • documents • data ...

What is Software? Software is a logical rather than a physical system element. Therefore, software has characteristics that are considerably different than those of hardware.   

software is engineered, not manufactured software doesn’t wear out software is complex teams of software specialists, each focusing on one part of the technology required to deliver a complex application.

Hardware vs Software Hardware

Software

 Manufactured  Wears out  Built using components  Relatively simple

Developed/engineered  Deteriorates  Custom built  Complex

Manufacturing vs. Development 

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Once a hardware product has been manufactured, it is difficult or impossible to modify. In contrast, software products are routinely modified and upgraded. In hardware, hiring more people allows you to accomplish more work, but the same does not necessarily hold true in software engineering. Unlike hardware, software costs are concentrated in design rather than production.

Wear vs. Deterioration Hardware wears out over time

Wear vs. Deterioration Software deteriorates over time

Component Based vs. Custom Built   

Hardware products typically employ many standardized design components. Most software continues to be custom built. The software industry does seem to be moving (slowly) toward component-based construction.

The Cost of Change 60-100x

1.5-6x 1x

Definition

Development

After release

Software costs 

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Software costs often dominate system costs. The costs of software on a PC are often greater than the hardware cost Software costs more to maintain than it does to develop. For systems with a long life, maintenance costs may be several times development costs Software engineering is concerned with cost-effective software development

Software Poses Challenges  

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How do we ensure the quality of the software that we produce? How do we meet growing demand and still maintain budget control? How do we upgrade an aging “Software plant?” How do we avoid disastrous time delays? How do we successfully institute new software technologies?

What is software engineering? 

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Software engineering is an engineering discipline which is concerned with all aspects of software production Software engineers should  adopt a systematic and organised approach to their work and  use appropriate tools and techniques  depending on the problem to be solved, the development constraints and the resources available

Software engineering vs. Computer science 

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Computer science is concerned with theory and fundamentals; software engineering is concerned with the practicalities of developing and delivering useful software Computer science theories are currently insufficient to act as a complete underpinning for software engineering

Software engineering vs. System engineering 

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System engineering is concerned with all aspects of computerbased systems development including hardware, software and process engineering. Software engineering is part of this process System engineers are involved in system specification, architectural design, integration and deployment

What are the attributes of good software? 

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The software should deliver the required functionality and performance to the user and should be maintainable, dependable and usable Maintainability  Software must evolve to meet changing needs Dependability  Software must be trustworthy Efficiency  Software should not make wasteful use of system resources Usability  Software must be usable by the users for which it was designed

What are the key challenges facing software engineering? 

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Coping with legacy systems, coping with increasing diversity and coping with demands for reduced delivery times Legacy systems  Old, valuable systems must be maintained and updated Heterogeneity  Systems are distributed and include a mix of hardware and software Delivery  There is increasing pressure for faster delivery of software

Software Applications   

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system software application software engineering/scientific software embedded software product-line software WebApps (Web applications) AI software

System Software  

Service other programs Usually:  heavy interaction with computer hardware,  heavy usage by multiple users,  concurrent operation  scheduling, resource sharing, process management,  complex data structures,  multiple external interfaces

Application Software 

Standalone programs that solve a specific business need.  Conventional data processing  Control business functions in real-time

Engineering/Scientific software  

Numerical algorithms Newly: real-time and system software characteristics

Including:  Astronomy  Volcano logy  Automotive stress analysis  Space shuttle orbital dynamics  Molecular biology

Embedded Software 

Resides within a product or system

Product-line software 

Provide a specific capability for use by many different customers

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Inventory control, word processing, spreadsheets, computer graphics, …

WebApps (Web applications) 

E- commerce and B2B applications

AI Software Robotics, expert systems, pattern recognition (image and voice), artificial neural networks, theorem proving, and game playing

Software – New Categories 

Ubiquitous computing—wireless networks

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Netsourcing—the Web as a computing engine

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Open source—”free” source code open to the computing community (a blessing, but also a potential curse!)

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Data mining

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Grid computing

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Cognitive machines

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Software for nanotechnologies

Legacy Software Why must it change?      

It must be fixed to eliminate errors. It must be enhanced to implement new functional and nonfunctional requirements Software must be adapted to meet the needs of new computing environments or technology. Software must be enhanced to implement new business requirements. Software must be extended to make it interoperable with other more modern systems or databases. Software must be re-architected to make it viable within a network environment.

Software Evolution 

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The Law of Continuing Change (1974): E-type systems must be continually adapted else they become progressively less satisfactory. The Law of Increasing Complexity (1974): As an E-type system evolves its complexity increases unless work is done to maintain or reduce it. The Law of Self Regulation (1974): The E-type system evolution process is self-regulating with distribution of product and process measures close to normal. The Law of Conservation of Organizational Stability (1980): The average effective global activity rate in an evolving E-type system is invariant over product lifetime.

Software Evolution 

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The Law of Conservation of Familiarity (1980): As an E-type system evolves all associated with it, developers, sales personnel, users, for example, must maintain mastery of its content and behavior to achieve satisfactory evolution. The Law of Continuing Growth (1980): The functional content of E-type systems must be continually increased to maintain user satisfaction over their lifetime. The Law of Declining Quality (1996): The quality of E-type systems will appear to be declining unless they are rigorously maintained and adapted to operational environment changes. The Feedback System Law (1996): E-type evolution processes constitute multi-level, multi-loop, multi-agent feedback systems and must be treated as such to achieve significant improvement over any reasonable base.

Software Myths Affect managers, customers (and other non-technical stakeholders) and practitioners  Are believable because they often have elements of truth, but …  Invariably lead to bad decisions, therefore …  Insist on reality as you navigate your way through software engineering 

Software Myths       

If we get behind schedule, we can add more programmers and catch up. A general statement about objectives is sufficient to begin building programs. Change in project requirements can be easily accommodated because software is flexible. Once we write a working program, we’re done. Until I get the program running, I have no way of assessing its quality. The only deliverable work product for a successful project is the working program. Software engineering will make us create too much documentation and will slow us down.

Management Myths 

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“We already have a book of standards and procedures for building software. It does provide my people with everything they need to know …” “If my project is behind the schedule, I always can add more programmers to it and catch up …” (a.k.a. “The Mongolian Horde concept”) “If I decide to outsource the software project to a third party, I can just relax: Let them build it, and I will just pocket my profits …”

Customer Myths 

“A general statement of objectives is sufficient to begin writing programs - we can fill in the details later …”

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“Project requirements continually change but this change can easily be accommodated because software is flexible …”

Practitioner’s Myths 

“Let’s start coding ASAP, because once we write the program and get it to work, our job is done …”

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“Until I get the program running, I have no way of assessing its quality …”

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“The only deliverable work product for a successful project is the working program …”

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“Software engineering is baloney. It makes us create tons of paperwork, only to slow us down …”