General, abstract definitions of quality have often been attempted.
The concept may be discussed for long and may give rise to different,
subjective formulations, each of them acceptable on the basis of some
points of view. What is interesting here, is that precisely defined
models can be proposed for quality. A quality model is a very general
concept: it can be conceived as a structured set of properties, or
characteristics, that can be established for an
object to declare it a quality object. The model can be used as a
guideline for developing an object or a reference to evaluate
properties of a software system.
For software systems, various quality models have been explicitly or
implicitly proposed (by Bogen, Deutsch, Azuma, Rae, et.al.). All of
them address a methodology to define a hierarchic structure of
characteristics and a way to relate these characteristics to some
technical aspects of the system. In literature, there is little
evidence of showing whether or not the characteristics depend on the
application domain the system belongs to. This point is even purposely
avoided, probably due to searching for a model as general as
possible. In fact, these and other efforts have led to define and
approve a very popular standard for software system quality, like the
ISO/IEC 9126 resp. ISO14598 or the QoS frameworks and guidelines.
The model referred by this standard defines quality as a set of six
characteristics (Functionality, Reliability, Usability,
Maintainability, Efficiency, Portability) and proposes a further
decomposition of each characteristic into a set of
sub-characteristic, wisely not included in the standard. Among the
great variety of software products, web portal have widely grown both
in the number of media and technologies involved and in the target
which they are addressed to.
