Promise Keynote

New Directions for Software Metrics Norman Fenton Agena Ltd and Queen Mary University of London PROMISE 20 May 2007

Overview
History of software metrics
Good and bad news
Hard project constraints
Project trade-offs
Decision-making and intervention
The true objective of software metrics?
Why we need a causal approach
Models in action
Results

Metrics History: Typical Approach What I really want to measure (Y) What I can measure (X) Y = f (X)

Metrics History: the drivers
‘ productivity’=size/effort
‘ effort’=a*size b
‘ quality’=defects/size

Metrics history: size matters!
LOC
Improved size metrics
Improved complexity metrics

Some Decent News About Metrics
Empirical results/banchmarks
Significant industrial activity
Academic/research output
Metrics in programmer toolkits

….But Now the Bad News
Lack of commercial relevance
Programmes doomed by data
Activity poorly motivated
Failed to meet true objective of quantitative risk assessment

Regression models….?

Using metrics and fault data to predict quality 0 0 Post-release faults 10 20 30 40 80 120 160 Pre-release faults ?

Pre-release vs post-release faults: actual Post-release faults 0 10 20 30 0 40 80 120 160 Pre-release faults

What we need What I think is... ?

The Good News
It is possible to use metrics to meet the real objective
Don’t need a heavyweight ‘metrics programme’
A lot of the hard stuff has been done

A Causal Model (Bayesian net) Residual Defects Testing Effort Problem complexity Defects found and fixed Defects Introduced Design process quality Operational defects Operational usage

A Model in action

https://intranet.dcs.qmul.ac.uk/courses/coursenotes/DCS235/

A Model in action

Actual versus predicted defects

How did we build the models?
Expert judgement
Published data
Company data

Conclusions
Heavyweight data and classical statistics NOT the answer
Empirical studies laid groundwork
Causal models for quantitative risk

… And
You can use the technology NOW
www.agenarisk.com

Promise Keynote

by promise07 on May 20, 2007

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Promise Keynote — Presentation Transcript