Specification of Reactive Hardware/Software Systems - Electronic ...

136 Concepts for the Integration of Specification and Design
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x Object A y z
Abstraction
u u a b
u
Object C
c
Cluster
Object B
Cluster used as
abstraction boundary
that hides all object
names.
Figure 5.10: Abstraction Boundary hiding Strongly Distributed Composite
difficult. This may be required to solve performance problems. Concurrency boundaries
are used to partition a system of parallel objects into pieces that behave sequentially. We
prescribe concurrency boundaries to be implemented as clusters. Under circumstances,
this may require the introduction of new clusters. A cluster that represents a concurrency
boundary, must be labelled with the abbreviation: SEQ, denoting sequential behaviour
(Figure 5.12). Its cluster class definition heading must be extended by a comment after
the cluster class name. This comment is:
’Cluster type: Sequential’
5.8.2.5 Distribution Boundary
Distribution boundaries decompose a (sub)system into physically separated parts. Such
a part is called a subsystem of distribution or a module of distribution.
Usually distribution boundaries notify that the communication on the channels must be
designed according to the properties of some physical and/or geographical separation.
A protocol must be used to implement abstract communication flows in an essential
model. Requirements such as throughput, minimum distance, etcetera, must be fulfilled.
Distribution boundaries must be represented as clusters in object instance models. A
cluster representing a distribution boundary must be labelled by the abbreviation DISTR
(see Figure 5.13 in Subsection 5.9.2). Its cluster class definition heading must be extended
by a comment after the cluster class name. This comment is
’Cluster type: Module of Distribution’
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HIDE
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