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Software Reliability


(Improving the Software Process Using Bayesian Nets)

Funding to CSr, City University: £220,892

Funding Source: EPSRC Project GR/L06683 

Note: This Project has been transfered to Queen Mary and Westfield College, University of London, since 1st April 2000. Contact Dr Martin Neil (martin@dcs.qmw.ac.uk) for further information.


Integrating novel research in safety and dependability assessment into mainstream software engineering process improvement. Developing a tool to predict specific software quality measures directly related to reliability and maintainability.


  • To use our past research results in dependability argumentation using Bayesian Belief Network's (BBN's) and decision analysis techniques to control and measure software quality,
  • to develop a BBN approach to statistical control of software processes and for prediction of the industry standard quality measure, defect density,
  • to implement these new BBN's in a demonstrator prototype for promotion within the research community and dissemination to industry.


  • A concise IMPRESS framework is being developed with the aim of recording the steps needed in quality decision making and quality argumentation.
  • Incorporating variables drawn from quality modelling, defect density prediction and process improvement, two BBN templates are to be developed predicting defect density and maintainability.
  • Specifying alternative methods for software Statistical Process Control
  • Developing a prototype demonstrator tool from an existing BBN tool.


Currently in mainstream software engineering, including the commercial sector, there is a continuing reliance on ill-conceived, ad-hoc methods for assessing the quality of processes and products. IMPRESS will provide a prototype tool that incorporates models of software quality, defect analysis and statistical process control for prediction of software quality measures directly related to reliability and maintainability.


In the long term, any industry which relies on high quality software products may benefit from this research. The medium-term beneficiaries will be software quality managers and independent assessors of software processes and products. Also consultants, tool developers and vendors. The short-term beneficiaries will be researchers in software quality and process improvement.

European Partners: HUGIN Expert A/S (Denmark).

CSR Personnel: Professor Fenton, Professor Littlewood, Dr. Neil, Professor Strigini, Mr. Lewis, and Mr. Makwana.

We welcome your feedback, please mail any comments/suggestions to webadm@soi.city.ac.uk
version 2.2 Published: 28th Jun 2004