28-06-2012, 03:35 PM
Reliability Models
[attachment=25969]
Definition of Software Reliability
Software reliability is defined as the probability of failure-free operation of a computer program in a specified environment for a specified time.
Two terms related to software reliability
Fault: a defect in the software, e.g. a bug in the code which may cause a failure
Failure: a derivation of the programs observed behavior from the required behavior
Software Reliability Models
Purpose
Software Reliability Models rely on observation of failure occurrence and try to predict future failure behavior
Two different models :
Basic Execution Time model
Logarithmic Poisson Execution Time Model
Basic Execution Time model
Developed by J.D Musa. So this model is also known as Musa’s Basic Model.
Based on Execution time
Assumptions:
1)Assume that failures may occur according to a Non-Homogeneous Poisson Process(NHPP).
E.g.. Expected number of persons visiting in a shopping mall in a given period of time.
This process is non homogeneous since the intensity changes as a function of time.
2) Assume that the decrement in failure intensity function is constant
[attachment=25969]
Definition of Software Reliability
Software reliability is defined as the probability of failure-free operation of a computer program in a specified environment for a specified time.
Two terms related to software reliability
Fault: a defect in the software, e.g. a bug in the code which may cause a failure
Failure: a derivation of the programs observed behavior from the required behavior
Software Reliability Models
Purpose
Software Reliability Models rely on observation of failure occurrence and try to predict future failure behavior
Two different models :
Basic Execution Time model
Logarithmic Poisson Execution Time Model
Basic Execution Time model
Developed by J.D Musa. So this model is also known as Musa’s Basic Model.
Based on Execution time
Assumptions:
1)Assume that failures may occur according to a Non-Homogeneous Poisson Process(NHPP).
E.g.. Expected number of persons visiting in a shopping mall in a given period of time.
This process is non homogeneous since the intensity changes as a function of time.
2) Assume that the decrement in failure intensity function is constant