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Essence and Accident

Inherent Difficulties Complexity Conformity Changeability Invisibility. Essence and Accident. Essence difficulties inherent in the nature of software Accidents difficulties encountered but not inherent . Reliability Portability Efficiency Human Engineering.

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Essence and Accident

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  1. Inherent Difficulties Complexity Conformity Changeability Invisibility Essence and Accident • Essence • difficulties inherent in the nature of software • Accidents • difficulties encountered but not inherent CSE1320 Intermediate Programming

  2. Reliability Portability Efficiency Human Engineering Software Engineering Processes attempt to maximize QUALITY in the form of: • Testability • Understandability • Modifiability CSE1320 Intermediate Programming

  3. Why? Issues concerning software quality Relative costs of fixing faults Price performance factors Product size increase leads to larger teams Software Engineering Processes CSE1320 Intermediate Programming

  4. Requirements Specifications Design Implementation Integration Maintenance Retirement What are the phases in the lifecycle of a software product? CSE1320 Intermediate Programming

  5. What does the problem require in terms of the solution? Written document Customer driven Requirements testing Rapid prototype Mock-up Partial system Requirements Phase“What I need, not what I said I needed” CSE1320 Intermediate Programming

  6. What does the product do? What are the constraints on the product? Acceptance criteria Frequent problems with a spec: ambiguous incomplete contradictory Specifications testing SQA reviews Specifications PhaseWhat the developer wants to know: CSE1320 Intermediate Programming

  7. Analysis of the problem Structured analysis : decomposing problem by how data is manipulated (acted upon) Object-oriented analysis: decomposing problem by how data is represented Developer must make design decisions about: algorithms data representations I/O interfaces data flow modules Design testing traceability Design PhaseHow does the product do what it is supposed to do? CSE1320 Intermediate Programming

  8. Code Documentation Tests Implementation testing desk checking test cases reviews Implementation PhaseInitial CS courses have to focus on this element first CSE1320 Intermediate Programming

  9. Composition order Integration testing interfaces Testing does it meet the specs? product testing by SQA acceptance testing by customer Integration PhasePutting it all together CSE1320 Intermediate Programming

  10. Maintenance testing changes regression testing Retirement cost-effective? Maintenance PhaseIn the user’s hands • Why? • operation • documentation • turnover • Kinds of maintenance • Corrective • Adaptive • Perfective • Preventive CSE1320 Intermediate Programming

  11. Specification principles • Separate functionality from implementation • A process-oriented systems spec language is required • A spec must encompass the system of which the SW is a component • A spec must encompass the environment in which the system operates • A system spec must be a cognitive model • A spec must be operational • The spec must be tolerant of incompleteness and augmentable • A spec must be localized and loosely coupled CSE1320 Intermediate Programming

  12. What differentiates one analysis technique from another? hueristics and notions point of view notation modeling approach What things are common about analysis methods? hierarchical representation external and internal interfaces design and implementation foundation no focus on constraints or validation Analysis principles and issues CSE1320 Intermediate Programming

  13. Analysis principles and issues • Analysis is information-driven • First provide a mechanism for representing info then derive function and behavior • Common characteristics • mechanism for info domain analysis • approach for functional and/or behavior representation • definition of interfaces • mechanisms for problem partitioning • support of abstraction • representation of essential and implementation views CSE1320 Intermediate Programming

  14. TestingTesting cannot show the absence of defects, it can only show that software defects are present. • Testing is a process of executing a program with the intent of finding an error. • A good test case is one that has a high probability of finding an as yet undiscovered error. • A successful test is one that uncovers an as yet undiscovered error. CSE1320 Intermediate Programming

  15. Testing Methods • Black-box testing • Knowing the specified function that a product has been designed to perform, tests can be conducted that demonstrate each function is fully operational. • White-box or glass-box testing • Knowing the internal workings of a product, tests can be conducted to ensure that "all the gears mesh". • independent paths at least once • logical decisions both true and false • loops • internal data structures CSE1320 Intermediate Programming

  16. Development Testing • Debugging approaches • brute force • backtracking • cause elimination • Before you fix • Is the cause of this bug also reproduced elsewhere? • What new bug might I be putting in? • What would have prevented this bug? CSE1320 Intermediate Programming

  17. Activities of SCM ID change control change ensure that change is properly implemented report change to others SCM output programs documentation data structures Software Configuration ManagementChange is inevitable SCM is not the same as maintenance CSE1320 Intermediate Programming

  18. Systems Engineering Issues Takes customer-defined goals and constraints and derives a representation of function, performance, interfaces, design constraints and information structure that can be allocated to each of the generic system elements available. CSE1320 Intermediate Programming

  19. Sources The Mythical Man-Month, Brooks, Frederick P.; Addison-Wesley Publishing Company, (Reprint)1982 “No Silver Bullet: Essence and Accidents of Software Engineering,”, Computer, Vol. 20, No. 4 (April 1987) pp. 10-19 Software Engineering,Schach, Stephen R.;Aksen Associates Incorporated Publishers, 1990 Software Engineering, A Practitioner’s Approach,Pressman, Roger S.;McGraw-Hill, Inc. 1992 Software Engineering, Design, Reliability,and Management,Shooman, Martin L.;McGraw-Hill, Inc. 1983 Software Engineering Metrics and Models, Conte, S.D., H.E. Dunsmore, V.Y. Shen;The Benjamin/Cummings Publishing Company, Inc., 1986 Software Engineering Notes for CSE1320 Intermediate Programming CSE1320 Intermediate Programming

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