Monday, August 11, 2008

Software engineering

The economies of ALL developed nations are dependent on software
More and more systems are software controlled
Software engineering is concerned with theories, methods and tools for professional software development
Software costs
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
What is software?
Computer programs and associated documentation (plus configuration data and user training)

Software products may be developed for a particular customer or developed for a general market
Generic (shrink-wrapped) - developed to be sold to a range of different customers
Bespoke (custom) - developed for a single customer according to their specification
What are the attributes of good software?
The software should deliver the required functionality and performance to the user and should be maintainable, dependable and usable
Software must evolve to meet changing needs
Software must be trustworthy
Software should not make wasteful use of system resources
Software must be usable by the users for which it was designed
...attributes of good software
(these two are not always required)
Software should fail only under extreme conditions
Should be possible to move from one environment to another

The software crisis
Advances in hardware technologies made it possible to build powerful computers
This allowed building of more complex and powerful software
Existing software development methodologies were not capable of handling such large projects.
Hence projects had many problems:
Over budget
Late delivery
Requirements not met
Poor usability

What is software engineering?
Software engineering is an engineering discipline which is concerned with all aspects of software production (Sommerville, 2001)
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
What is the difference between software engineering and system engineering?
System engineering is concerned with all aspects of computer-based 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
Why does a software engineer need to understand system engineering aspects?
Many software systems are part of a larger system
System engineering decisions have direct impacts on software
Many systems now have lots of software parts
What is a software process?
A set of activities and associated results whose goal is the development or evolution of a software product
Generic (general) activities in all software processes are:
Specification - what the system should do and its development constraints
Development - production of the software system
Validation - checking that the software is what the customer wants
Evolution - changing the software in response to changing demands
What are software engineering methods?
Structured approaches to software development which include system models, notations, rules, design advice and process guidance
Model descriptions
Descriptions of graphical models which should be produced
Constraints applied to system models
Advice on good design practice
Process guidance
What activities to follow
What is CASE ? (Computer-Aided Software Engineering)
Software systems which are intended to provide automated support for software process activities. CASE systems are often used for method support
Tools to support the early process activities of requirements and design
Tools to support later activities such as programming, debugging and testing
What are the costs of software engineering?
Roughly 60% of costs are development costs, 40% are testing costs. For custom software, evolution costs often exceed development costs
Costs vary depending on
the type of system being developed and
the requirements of system attributes such as performance and system reliability
Distribution of costs depends on the development model that is used
What are the key challenges facing software engineering?
Coping with legacy (old) systems, coping with increasing diversity (variety) and coping with demands for reduced delivery times
Legacy systems
Old, valuable systems must be maintained and updated
Systems are distributed and include a mix of hardware and software
There is increasing pressure for faster delivery of software
Professional and ethical responsibility
Software engineering involves wider responsibilities than simply the application of technical skills.
Software engineers must behave in an honest and ethically (morel, principled) responsible way if they are to be respected as professionals.
Issues of professional responsibility
Engineers should normally respect the confidentiality (privacy) of their employers or clients irrespective of whether or not a formal confidentiality agreement has been signed.
Engineers should not misrepresent their level of competence (capability). They should not knowingly accept work which is outside their competence.

Issues of professional responsibility
Intellectual property rights
Engineers should be aware of local laws governing the use of intellectual (scholar) property such as patents (exclusive rights), copyright, etc. They should be careful to ensure that the intellectual property of employers and clients is protected.
Computer misuse
Software engineers should not use their 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 (distribution) of viruses).
Ethical dilemmas
Disagreement in principle with the policies of senior management
Your employer acts in an unethical way and releases a safety-critical system without finishing the testing of the system
Participation in the development of military weapons systems or nuclear systems

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