Software Quality and Standards.pdf

Software Quality and Standards

Dr. James A. Bednar

jbednar@inf.ed.ac.uk

http://homepages.inf.ed.ac.uk/jbednar

Dr. David Robertson

dr@inf.ed.ac.uk

http://www.inf.ed.ac.uk/ssp/members/dave.htm

SEOC2 Spring 2005: Quality/Standards

What is Software Quality?

• High quality software meets the needs of users while

being reliable, well supported, maintainable, portable,

and easily integrated with other tools.

• Is higher quality better? Is it more expensive?

Not always, on both counts.

• We will look at how to achieve quality, the tradeoffs

involved, modeling quality improvement, and standards

designed to ensure quality.

SEOC2 Spring 2005: Quality/Standards

Cost/Beneﬁt Tradeoff

Making changes to improve software quality requires time

and money to:

• Spot the problem

• Isolate its source

• Connect it to the real cause

• Fix the requirements, design, and code

• Test the ﬁx for this problem

• Test the ﬁx has not caused new problems

• Change the documentation

For a given change to make sense, the improvement

needs to pay for all these tasks, plus the revenue lost

during the delay in the product release.

SEOC2 Spring 2005: Quality/Standards

Feature/Bug Tradeoff

• Meeting the needs of users (not to mention marketing)

requires adding features.

• However, given a ﬁxed amount of development time and

money, adding features adds bugs and reduces time for

testing.

• Do the features increase user productivity more than the

bugs decrease it?

• Difﬁcult to answer this question, because data on users

is sparse, and other factors like reputation usually take

precedence.

SEOC2 Spring 2005: Quality/Standards

Quality for free?

But is increasing quality always more expensive, in terms

of total cost of production and maintenance? No.

In fact, if you focus on quality from the start, then:

• You tend to produce components with fewer defects, so

• You spend less time debugging, so

• You have more time in your schedule for improving

other aspects of quality, like usability

SEOC2 Spring 2005: Quality/Standards

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