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

94 Abstraction of a Problem Domain
The following list describes sharing related to the concepts of data object, process object,
composite, aggregate and cluster:
data objects can share a data object;
composites of data objects can share a data object;
process objects can share a process object;
process objects cannot share a data object;
composites of process objects can share a process object;
aggregates cannot share an object that is contained in one of the aggregates;
clusters can share a process object or a cluster.
Notice that separate clusters can share a process object but they cannot contain the same
process object. Two (clustered) composites share a part if there are two or more entities,
at least one of each (clustered) composite, that share that part.
4.8.6 Inseparability
An entity is inseparable from another entity, if the latter entity depends on the former
entity for its entire ’lifetime’. The definition can be clarified with the aggregate in Figure
a
a
d
Object C
(Part)
Aggregate
object
(Whole)
f
Cluster
b
e c
Object B
(Part)
Figure 4.23: An Inseparable Aggregate
4.23. The object C is inseparable from the aggregate object if the whole depends on this
part for its entire lifetime. Message flow ’d’ requests for a service that the aggregate
(object) needs. Therefore the aggregate depends on C. The part cannot be separated.
The concept of inseparability is useful, because analysis may bring in composites that
have such a property. So these composites must be designed such that they are inseparable.
b
c