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reliable embedded systems that take into account the contexts


This paper proposes a new style of product line engineering (PLE) [2] method
for constructing reliable embedded systems that take into account the contexts
such as the external physical environments. Many of the embedded systems not
only affect their environments through actuators but also are affected by their
environments through sensors. In this paper, the term context refers to the real
world such as the usage environments that affect the system behavior. It is
important to provide a context-dependent development method for constructing safe and reliable systems. Although all of the embedded systems are not
necessarily context-dependent, many of the consumer appliances such as mobile
phone, air conditioner, and car electronics are context-dependent. If fatal defects
are included in these products, the large-scale recall is not avoidable. The goal
of this paper is to improve the reliability of such kinds of embedded systems.
PLE is a promising approach to developing embedded systems. In PLE, a
product is constructed by assembling core assets, components reused in a family
of products. These core assets are identified by analyzing characteristics needed
in a family of products. This activity is called the feature analysis
In the current PLE, the feature analysis is mainly conducted from the viewpoint of system configurations: how hardware and software components are configured to construct a system—the contexts are not considered explicitly in most
cases. As a result, unexpected and unfavorable behavior might emerge in a system if a developer does not recognize any possible conflicting combinations between the system and contexts. This behavior might cause a crucial accident.
It, however, is not easy to detect this behavior only by reviewing each of system
and context requirements because this unfavorable behavior emerges through
incidental combinations of a system and contexts. It is important to detect the
unfavorable behavior systematically at the early stage of the development.
To deal with the above problem, this paper proposes the notion of a contextdependent PLE in which a product line is divided into two kinds of lines: the
system line and the context line. The former is a line obtained by analyzing
the features of hardware and software components that consist of a family of
systems. The latter is obtained by analyzing the features of contexts.
In the proposed method, each feature description is specified using VDM++
[4], a language for lightweight formal approaches in which formal methods are
used as a tool for describing the essential aspects of systems rigorously. VDM++
is an object-oriented extension of VDM-SL (The Vienna Development Method
– Specification Language) [5], a formal specification language for the rigorous
software modeling. VDM++ is one of the most popular formal methods in Japan.
The Mobile Felica Chip project in Japan developed a very large embedded system
using VDM++. In this project [18], the specification included over 100,000 lines
of VDM++. For such a reason, we adopted VDM++ for feature descriptions.
The correctness of the configuration of selected hardware components, software
components, and contexts can be formally validated at the specification level by
using VDMTools [21], a tool for supporting VDM++.
The remainder of this paper is structured as follows. In Section 2, problems in
the current PLE is pointed out. In Section 3, the context-dependent PLE method
is introduced to deal with the problems. In Section 4, a method for describing the
core asset specifications and validating them is provided. In Section 5, related
work is introduced. Concluding remarks are provided in Section 6.

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