1 / 13

SENG 521 Software Reliability & Testing

SENG 521 Software Reliability & Testing. Defining Necessary Reliability (Part 3a). Department of Electrical & Computer Engineering, University of Calgary B.H. Far ( far@enel.ucalgary.ca ) http://www.enel.ucalgary.ca/~far/Lectures/SENG521/03a/. Error. cause. Fault. cause. Failure.

margo
Download Presentation

SENG 521 Software Reliability & Testing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. SENG 521Software Reliability & Testing Defining Necessary Reliability (Part 3a) Department of Electrical & Computer Engineering, University of Calgary B.H. Far (far@enel.ucalgary.ca) http://www.enel.ucalgary.ca/~far/Lectures/SENG521/03a/ far@enel.ucalgary.ca

  2. Error cause Fault cause Failure Error - Fault - Failure • An error is a human action that results in software containing a fault. • A fault (bug) is a cause for either a failure of the program or an internal error (e.g., an incorrect state, incorrect timing). • Among the 3 factors only failure is observable. far@enel.ucalgary.ca

  3. Necessary Reliability: How to • Define failure with “failure severity classes (FSC)” for the product. • Choose a common measure for all associated systems. • Set a “failure intensity objective (FIO)” for each system to be tested. • Find the developed software failure intensity objective. • Engineer strategies to meet the software failure intensity objective. far@enel.ucalgary.ca

  4. Failure Severity Classes • Failures usually differ by their impact on the system • A failure Severity Class (FSC) is a set of failures that have the same per-failure impact on users using a failure classification criteria • Common classification criteria: • cost, system capability, human life, environment • Failure severity is different from its complexity • Severity can change with the time of failure far@enel.ucalgary.ca

  5. FSC: Common Classification • Common classification criteria: Cost • What does this failure cost in terms of operational cost, repair cost, loss of business, disruption, etc. • Severity classes based on cost may be scaled by a factor of 10. • Usually 4 ranges are enough. far@enel.ucalgary.ca

  6. FSC: Common Classification • Common classification criteria: System capability • May include factors such as loss of data, downtime, recoverability, etc. far@enel.ucalgary.ca

  7. FSC: Common Classification • Common classification criteria: Environment • May include factors such as harmful to environment, loss of wild life, etc. • Applicable to nuclear, chemical industry, etc. far@enel.ucalgary.ca

  8. FSC: Common Classification • Common classification criteria: Human life • May include factors such as harmful to human or environment, loss of human life, etc. • Applicable to aeronautical, automotive, nuclear, health care industry, military systems, etc. far@enel.ucalgary.ca

  9. How to Define FSC • Experience based. • List all factors that may be considered as failure severity for the project • Narrow the list down to the most critical and/or measurable ones • Some factors may be hard to measure, such as impact on company reputation, etc. far@enel.ucalgary.ca

  10. Failure Intensity Objective • Failure intensity is defined as failure per natural units, e.g. • 3 alarms per 100 hours of operation. • 5 failures per 1000 print jobs, etc. • Failure intensity of a system is the sum of failure intensities for all of the components of the system. far@enel.ucalgary.ca

  11. How to Set FIO /1 • Mainly experience based. • Depends on the project. • Depends on the trade-off among quality characteristics (development time and development cost) and functionality and technology. far@enel.ucalgary.ca

  12. How to Set FIO /2 • Typical FIO for various projects far@enel.ucalgary.ca

  13. How to Set FIO /3 • Setting FIO in terms of reliability λ is failure intensity R is reliability t is natural unit (time, etc.) • For λ=0.001 reliability is around 0.992 for 8 natural units. far@enel.ucalgary.ca

More Related