Environmental Engineering Reference
In-Depth Information
for methods and means of diversity
implementation.
c. Software is a multi-component system.
During the statement and classification
of requirements the purpose, level of
approval and safety class of differ-
ent software components have to be
considered.
d. Software is a product and a process.
This feature of software is one of the
critical ones in selecting classification
features of requirements and generation
of their complete sets, which considers
the certain influence of development
and verification processes on software
characteristics.
4. The existing regulations, which include stan-
dards determining software requirements.
On the basis of these standards requirements
for I&C software can be selected as the so-
called normative profile for software. In the
general case normative profile is a subset
and/or combinations of the positions of
basic standards for a specific subject area,
which are required for implementation of
the required functions in the system. In
this case, we mean the normative profile of
requirements for I&C software that is im-
portant for nuclear power plant safety. The
said standards form the profile-forming base
for producing the normative profile of soft-
ware requirements (for example, software
lifecycle models, structure of requirements
for software, set of metrics and methods of
evaluation, requirements for tools, etc.).
5. Possible variants of requirement structuring.
This factor is conceptual in nature, because
it determines the general approaches, prior-
ity and interconnection between different
requirements for I&C software. Several
variants of software requirements structuring
are possible:
a. Product-oriented: requirements that
determine characteristics for software
as a component of I&C system. It
does not take into account the fact that
software characteristics are built in and
implemented at different stages of the
software lifecycle.
b. Process-oriented: requirements corre-
spond to software lifecycle processes
and define features of process and
intermediate product of each stage in
the form of “stage-tasks-requirements”
statements. This approach is widely
used and allows clear process manage-
ment and quality assurance, but compli-
cates the definition of software product
features and for complex software can
lead to difficulties with integration.
c. Mixed process-product-oriented: re-
quirement are divided in two groups
and describe both features of develop-
ment processes and features of final
product. In this case the advantages
of the first two approaches are used.
General and Functional
Requirements
The classification of software requirements can be
performed in two stages: in the first stage, which
corresponds to the upper level of the hierarchy,
we determine the place of normative requirements
among the full set of requirements for software
(classification of kinds of requirements for soft-
ware); in the second stage, which corresponds to
the lower level of the hierarchy, we carry out the
classification of general requirements for software,
based on the process-product approach.
The set of requirements for software corre-
sponds to the set of requirements for I&C system,
because it contains both requirements and func-
tions, and for their quality (properties), and to
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