Background - Using Event-B for Critical Device Software Systems - page 25

process is traceable using reverse engineering technique to the actual stakeholders
requirements. The quality of a system can be assessed through predefined criteria
for a good design. Analysis and design methods for software have been evolving
over the years, each with its approach for modelling needs a world-view into soft-
ware [ 86 ]. The following methodologies are common, which are used in current
practices.

• Structured Analysis and Structured Design (SA/SD)

• Object Oriented Analysis and Object Oriented Design (OOA/OOD)

• Formal Methods (FM) and Model-based Development

SA/SD techniques provide means to create and evaluate a good design of the
systems. This technique covers functional decomposition, data flow and informa-
tion modelling. OOA/OOD considers the whole system into abstract entities called
objects, which can contain information (data) and have associated behaviour. It is
in practice from last 30 years, which is used in several big projects. It contains
Object-Oriented Analysis and Design (OOA/OOD) method, Object modelling Tech-
nique (OMT) Object-Oriented Analysis and Design with Applications (OOADA),
Object-Oriented Software Engineering (OOSE) and UML. Formal Methods (FM)
and Model-based development are a set of techniques and tools based on mathe-
matical modelling and formal logic that are used to specify and verify requirements
and designs for the systems and software [ 86 ]. Formal method is also a process that
allows the logical properties of a computer system to be predicted from a mathe-
matical model of a system by means of a logical calculation. Formal methods can
be used for formal specification, formal verification and software models (with au-
tomatic code generation) [ 86 ].

2.7.1 Design for Reliability

Reliability is an attribute of a system that is derived from research, concept and
design through analysing the capacity and performance under the working environ-
ment. The reliability level can be established during design phase of the system
development. However, a subsequent testing and production cannot improve the re-
liability without any modification in the basic design. Design reliability techniques
integrating with the development process for assuring the safety of a system. Reli-
ability becomes a difficult design parameter due to the increasing complexity and
limited knowledge of the system requirements. If reliability is an important attribute
of a system then it is quantified during specification of the design requirements.
Reliability is essential for a healthcare and medical devices, which need to be
safe and effective. Medical device manufacturers and regulating bodies like the
Food and Drug Administration (FDA) [ 33 ] and Center for Devices and Radiological
Health (CDRH) [ 22 ] have a responsibility for assuring the safety and effectiveness
of medical devices. The CDRH has standards to analyse system specification, de-
sign requirements, and usability of a system. The CDRH [ 22 ] requires a complete