Wednesday, May 2, 2012

Importance and Consequences of bugs

 The importance of bugs depends on frequency, correction cost, installation cost, and consequences.
  1. Frequency: How often does that kind of bug occur? Pay more attention to the more frequent bug types.
  2. Correction Cost: What does it cost to correct the bug after it is found? The cost is the sum of 2 factors: (1) the cost of discovery (2) the cost of correction. These costs go up dramatically later in the development cycle when the bug is discovered. Correction cost also depends on system size.
  3. Installation Cost: Installation cost depends on the number of installations: small for a single user program but more for distributed systems. Fixing one bug and distributing the fix could exceed the entire system's development cost.
  4. Consequences: What are the consequences of the bug? Bug consequences can range from mild to catastrophic.

A reasonable metric for bug importance is
Importance= ($) = Frequence * (Correction cost + Installation cost + Consequential cost)

  • CONSEQUENCES OF BUGS: The consequences of a bug can be measure in terms of human rather than machine. Some consequences of a bug on a scale of one to ten are:
    1. Mild: The symptoms of the bug offend us aesthetically (gently); a misspelled output or a misaligned printout.
    2. Moderate: Outputs are misleading or redundant. The bug impacts the system's performance.
    3. Annoying: The system's behaviour because of the bug is dehumanizing. E.g. Names are truncated orarbitarily modified.
    4. Disturbing: It refuses to handle legitimate (authorized / legal) transactions. The ATM wont give you money. My credit card is declared invalid.
    5. Serious: It loses track of its transactions. Not just the transaction itself but the fact that the transaction occurred. Accountability is lost.
    6. Very Serious: The bug causes the system to do the wrong transactions. Instead of losing your paycheck, the system credits it to another account or converts deposits to withdrawals.
    7. Extreme: The problems aren't limited to a few users or to few transaction types. They are frequent and arbitrary instead of sporadic infrequent) or for unusual cases.
    8. Intolerable: Long term unrecoverable corruption of the database occurs and the corruption is not easily discovered. Serious consideration is given to shutting the system down.
    9. Catastrophic: The decision to shut down is taken out of our hands because the system fails.
    10. Infectious: What can be worse than a failed system? One that corrupt other systems even though it doesnot fall in itself ; that erodes the social physical environment; that melts nuclear reactors and starts war.

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