The document discusses several software quality models: - McCall's 1977 model identified quality factors like maintainability, flexibility, and testability from the user's perspective. Each factor has criteria and metrics. - Boehm's 1978 model has high-level, intermediate, and primitive characteristics contributing to overall quality. Intermediate factors include portability, reliability, and usability. - Gilb's 1988 model emphasizes defining attributes important to users and required quality levels. Attributes have sub-attributes to aid measurement.

1. SOFTWARE
QUALITY MODELS
Santiago UribeVelasquez
Gestion de la calidad de software
Universidad Pontificia Bolivariana

2. What is quality?
In the context of software engineering, software quality
refers to two related but distinct notions that exist
wherever quality is defined in a commercial context:
■ The functional quality of the software reflects how
well it meets or fits a given design, based on
functional requirements or specifications.
■ The structural quality of software refers to how it
complies with non-functional requirements that
support the delivery of functional requirements,
such as strength or maintainability.

3. Measurement of quality
■ Quality, like beauty, is in the eye of the beholder
■ From the point of view of the measurement, it must
have a precise definition in terms of software
attributes that are of interest to the user
■ In general, these are external attributes, however,
many proposals measure and analyze internal
attributes because they consider them as predictors
of external ones.
The internal attributes have two advantages:
■ They are available for earlier measurement
■ They are easier to measure

4. Initial models of quality
From the beginning of software
engineering, it was observed that the
quality is composed of a composition of
many characteristics
■ A quality model then describes these
characteristics and their relationships
■ Many models make diffuse the
distinction between internal and
external attributes, which makes the
understanding of the concept of quality
difficult

5. McCall Quality Model (1977)
■ McCall's model was the first to be
presented in 1977, and originated
motivated by US Air Force and DoD
■ Focuses on the final product,
identifying key attributes from the
user's point of view
■ These attributes are called quality
factors and are usually external
attributes, but some internal
attributes are also included

6. McCall Quality Model (1977)
■ The quality factors are too abstract to be
measured directly, so for each of them low-
level attributes called quality criteria are
introduced
■ Some quality criteria are internal attributes,
reflecting McCall's belief that the internal
attribute has a direct effect on the
corresponding external attribute
■ One more level of decomposition is
necessary, mapping each quality criterion
into a set of quality metrics that are
attributes (both of the product and the
process) of very low level, directly
measurable

7. McCall Quality Model (1977)
McCall proposes three perspectives to
group quality factors
■ Product revision
■ Product transition
■ Product operation

8. McCall Quality Model (1977)
The Product revision includes the
following quality factors:
■ Maintainability
■ Flexibility
■ Testability

9. McCall Quality Model (1977)
Maintainability includes the following
criteria:
■ Consistency
■ Simplicity
■ Thoroughness
■ Self Description
■ Modularity
Maintainability is strongly influenced by
the use of good practices throughout
the development cycle
■ Follow a well-defined methodology
■ Use good design techniques, both
procedures and data, to increase
cohesion and reduce coupling
■ Observe the internal documentation
■ Use good programming practices:
significant names, readable code,
etc.

10. McCall Quality Model (1977)
According to McCall, the flexibility factor
includes the following criteria:
■ Expansibility
■ Generality
■ Self Description
■ Modularity

11. McCall Quality Model (1977)
According to McCall, the factor of
testability includes the following criteria:
■ Simplicity
■ Instrumentation

12. Boehm Quality Model (1978)
■ The second best known quality
model
■ This model introduces high level
characteristics, intermediate level
characteristics and primitive
characteristics, each of which
contributes to the overall level of
quality

13. Boehm Quality Model (1978)
High-level characteristics represent
general requirements for use
■ Utility per-se how (usable, reliable,
efficient) is the product itself
■ Maintainability how easy it is to
modify it, understand it and rethink
it
■ General utility if it can continue to be
used if the environment changes

14. Boehm Quality Model (1978)
The intermediate level characteristics
represent the quality factors of Boehm:
■ Portability (general utility)
■ Reliability (utility per-se)
■ Efficiency (utility per-se)
■ Usability (utility per-se)
■ Testability (maintainability)
■ Ease of understanding (maintainability)
■ Modifiability or flexibility (maintainability)

15. Boehm Quality Model (1978)
The lowest level corresponds to
characteristics directly associated with
one or two quality metrics
■ Portability
■ Reliability
■ Efficiency
■ Usability
■ Testability

16. Gilb Quality Model (1988)
■ This model presents as a
fundamental aspect the definition of
the quality attributes that really
interest the user and the level of
quality that each of them must have
to satisfy it since it does not make
sense to demand quality in a
product, if it does not have this basis.
Each attribute has sub attributes
that help the measurement

17. Gilb Quality Model (1988)
Advantage
■ This model evaluates independently
■ Like other processes, it uses levels of
hierarchies to delegate work
Disadvantages
■ Many factors that cause more work
in time and costs are evaluated

18. The 8 Dimensions of Garvin's Quality
■ Performance
■ Features (Additional Functions)
■ Reliability
■ Design Conformity
■ Durability
■ Quality of service
■ Esthetic
■ Perceived quality