Essence and Accident

1
Essence and Accident

• Essence
• difficulties inherent in the nature of software
• Accidents
• difficulties encountered but not inherent

• Inherent Difficulties
• Complexity
• Conformity
• Changeability
• Invisibility

2
Software Engineering Processes attempt to
maximize QUALITY in the form of

• Testability
• Understandability
• Modifiability

• Reliability
• Portability
• Efficiency
• Human Engineering

3
Software Engineering Processes

• Why?
• Issues concerning software quality
• Relative costs of fixing faults
• Price performance factors
• Product size increase leads to larger teams

4
What are the phases in the lifecycle of a
software product?

• Requirements
• Specifications
• Design
• Implementation

• Integration
• Maintenance
• Retirement

5
Requirements Phase What I need, not what I said
I needed

• What does the problem require in terms of the
  solution?
• Written document
• Customer driven

• Requirements testing
• Rapid prototype
• Mock-up
• Partial system

6
Specifications PhaseWhat the developer wants to
know

• 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

7
Design PhaseHow does the product do what it is
supposed to do?

• 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

8
Implementation PhaseInitial CS courses have to
focus on this element first

• Code
• Documentation
• Tests

• Implementation testing
• desk checking
• test cases
• reviews

9
Integration PhasePutting it all together

• Composition order
• Integration testing
• interfaces

• Testing
• does it meet the specs?
• product testing by SQA
• acceptance testing by customer

10
Maintenance PhaseIn the users hands

• Why?
• operation
• documentation
• turnover
• Kinds of maintenance
• Corrective
• Adaptive
• Perfective
• Preventive

• Maintenance testing
• changes
• regression testing
• Retirement
• cost-effective?

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

12
Analysis principles and issues

• 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

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

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.

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

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?

17
Software Configuration ManagementChange is
inevitable

• Activities of SCM
• ID change
• control change
• ensure that change is properly implemented
• report change to others

• SCM output
• programs
• documentation
• data structures

SCM is not the same as maintenance
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.

19
Software Engineering Notes for CSE1320
Intermediate Programming

• 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 Practitioners
  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. ShenThe
  Benjamin/Cummings Publishing Company, Inc., 1986