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際際滷s chapter 1

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Priyanka Shetty
Priyanka Shetty

The document discusses several key aspects of software and software engineering: 1. Software serves both as a product that transforms information and as a vehicle that delivers computing capabilities. It controls programs, enables communications, and helps build other software. 2. Software is more complex and difficult to develop than hardware but easier to modify and upgrade. Software costs are concentrated in design rather than production. 3. Software evolves and deteriorates over time unlike hardware, which wears out. Most software continues to be custom built despite a slow trend toward component-based construction. Maintaining and evolving legacy software poses challenges. 4. The document outlines several "laws" and myths regarding software evolution, management, customers, and practitioners

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Chapter 1 Software and Software Engineering Software Engineering: A Practitioners Approach, 6th edition by Roger S. Pressman
Softwares Dual Role Software is a product Transforms information - produces, manages, acquires, modifies, displays, or transmits information Delivers computing potential of hardware and networks Software is a vehicle for delivering a product Controls other programs (operating system) Effects communications (networking software) Helps build other software (software tools & environments)
Software Applications system software application software engineering/scientific software embedded software product-line software web applications AI software
Hardware vs. Software Developed/engineered Deteriorates Custom built Complex Manufactured Wears out Built using components Relatively simple Software Hardware
Manufacturing vs. Development 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.
Software Complexity I believe the hard part of building software to be the specification, design, and testing of this conceptual construct, not the labor of representing it and testing the fidelity of the representation . If this is true, building software will always be hard. There is inherently no silver bullet. - Fred Brooks, No Silver Bullet http://www.computer.org/computer/homepage/misc/Brooks/
Legacy Software It must be fixed to eliminate errors. It must be enhanced to implement new functional and non-functional 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 . Why must it change?
E-Type Systems E-Type Systems: Software that has been implemented in a real-world computing context and will therefore evolve over time
Software Evolution 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. Source: Lehman, M., et al, Metrics and Laws of Software EvolutionThe Nineties View, Proceedings of the 4th International Software Metrics Symposium (METRICS '97), IEEE, 1997, can be downloaded from : http://www.ece.utexas.edu/~perry/work/papers/feast1.pdf
Software Evolution 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. Source: Lehman, M., et al, Metrics and Laws of Software EvolutionThe Nineties View, Proceedings of the 4th International Software Metrics Symposium (METRICS '97), IEEE, 1997, can be downloaded from : http://www.ece.utexas.edu/~perry/work/papers/feast1.pdf
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.
Software Myths Once we write a working program, were 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 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 Project requirements continually change but this change can easily be accommodated because software is flexible
Practitioners Myths Lets start coding ASAP, because once we write the program and get it to work, our job is 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 is baloney. It makes us create tons of paperwork, only to slow us down

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際際滷s chapter 1

  • 1. Chapter 1 Software and Software Engineering Software Engineering: A Practitioners Approach, 6th edition by Roger S. Pressman
  • 2. Softwares Dual Role Software is a product Transforms information - produces, manages, acquires, modifies, displays, or transmits information Delivers computing potential of hardware and networks Software is a vehicle for delivering a product Controls other programs (operating system) Effects communications (networking software) Helps build other software (software tools & environments)
  • 3. Software Applications system software application software engineering/scientific software embedded software product-line software web applications AI software
  • 4. Hardware vs. Software Developed/engineered Deteriorates Custom built Complex Manufactured Wears out Built using components Relatively simple Software Hardware
  • 5. Manufacturing vs. Development 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.
  • 6. Wear vs. Deterioration Hardware wears out over time
  • 7. Wear vs. Deterioration Software deteriorates over time
  • 8. 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.
  • 9. Software Complexity I believe the hard part of building software to be the specification, design, and testing of this conceptual construct, not the labor of representing it and testing the fidelity of the representation . If this is true, building software will always be hard. There is inherently no silver bullet. - Fred Brooks, No Silver Bullet http://www.computer.org/computer/homepage/misc/Brooks/
  • 10. Legacy Software It must be fixed to eliminate errors. It must be enhanced to implement new functional and non-functional 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 . Why must it change?
  • 11. E-Type Systems E-Type Systems: Software that has been implemented in a real-world computing context and will therefore evolve over time
  • 12. Software Evolution 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. Source: Lehman, M., et al, Metrics and Laws of Software EvolutionThe Nineties View, Proceedings of the 4th International Software Metrics Symposium (METRICS '97), IEEE, 1997, can be downloaded from : http://www.ece.utexas.edu/~perry/work/papers/feast1.pdf
  • 13. Software Evolution 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. Source: Lehman, M., et al, Metrics and Laws of Software EvolutionThe Nineties View, Proceedings of the 4th International Software Metrics Symposium (METRICS '97), IEEE, 1997, can be downloaded from : http://www.ece.utexas.edu/~perry/work/papers/feast1.pdf
  • 14. 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
  • 15. 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.
  • 16. Software Myths Once we write a working program, were 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.
  • 17. Management Myths 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
  • 18. Customer Myths A general statement of objectives is sufficient to begin writing programs - we can fill in the details later Project requirements continually change but this change can easily be accommodated because software is flexible
  • 19. Practitioners Myths Lets start coding ASAP, because once we write the program and get it to work, our job is 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 is baloney. It makes us create tons of paperwork, only to slow us down

Editor's Notes

  1. Information transformer - function behavior Computing potential - non-functional behavior Example of functional behavior? Type characters into keyboard => word processor displays them on screen Input program file => compiler translates to byte code Example of non-functional behavior? Type character in instant messenger => appears on friends screen Compile large program within a few seconds Performance - time and space Vehicle for product delivery Examples of SW controllers (other than OS) Examples of communication SW Examples of development tools