Software Quality

Software Quality

1. Notion of Quality

   • Garvins definitions of qual
     • Transcendent view
       • Qual is universally recognisable. its related to a comparison of features and characteristics of products
     • Product based view
       • Quality is a precise and measurable variable.
       • Differences in quality reflect the differences in quantities in some product attributes
     • user based view
       • quality is the fitness for intended users
     • manufacturing based view
       • quality is conformation to spec
     • value based view
       • quality product is one that provides performance at an acceptable price or conformance at an acceptable cost

2. software qual models

   • factors that affect software qual
     • attributes directly indicate, eg. reliability, correctness etc.
     • attributes indirectly related eg. internal complexity
     • interrelations between the factors
       • causality models: casual relationship in terms of stereotype relations
       • Quantitative models
         • quantitative relations expressed as numerical functions
         • Numerical values of the basic attributes are given
         • the overall quality in an attribute on a more high level of abstraction is calculates numerically
   • Hierarchical Models
     • set of related properties organised into hierarchical structure
       • decompose qual into a number of qual attributes and attributes into a no of factors, then a no of measures
       • positive casual relationship is represented
     • McCall model (1977)
     • ISO 9126 Model
   • Relational Models of SQ
     • qual model consists of
       • A number of qual attributes and factors etc
       • a set of stereo types of relationships between them. normally include
         • Positive relation - high on one aspect implies inevitably high on the other
         • Negative relation - high on one aspect of qual implies low on the other
         • Neutral relation - High or low on one doesnt imply the other is high or low
     • Perry Model (1991)
     • Gillies model (1992, 1997)

3. Software qual attributes

   • not all attributes are of equal importance
   • An attribute may have diff importance in diff software system
   • The importance of qual attribute for a given software may change as time passes
   • Relationships between atrributes are very complicated
   • Diff people have diff views on qual

4. Key features of existing SQ mdels

5. Uses of SQ models

   • Understanding software qual
     • To measure an existing systems qual
     • To predict a systems qual during development
     • To analyse qual probs during development and/or in operation of a systems
   • guidelines to development activites
     • To elicit users reqs on SQ
     • To perform qual assurance activities in software development and maintenance

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