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their supporting basic engineering objects. If there is replication, one com-
putational object corresponds exclusively to a single set of basic engineering
objects; in figure 7.1, for example, the computational objectCO
3
corresponds
to the set containingBEO
3a
andBEO
3b
.
This deals with most computational objects, but not all. Computational
binding objects are special because they encapsulate communications facilities.
Binding objects, or primitive bindings of interfaces, are required to correspond
either to engineering channels or to local interactions within clusters. There
are also rules to ensure that computational actions are refined in a consistent
way when elaborated as more detailed dialogues.
These are very simple constraints, but there will also be many more
domain-specific constraints. To help the specifier organize these, the
UML4ODP standard includes a number of checklists, in the form of metarules
for identifying the kind of correspondence statements needed to link the dif-
ferent viewpoints. As an example, it states that, for each enterprise object
in the enterprise specification, the specifier shall indicate the configuration of
computational objects that realizes the required enterprise behaviour. Simi-
larly, for each interaction in the enterprise specification, they shall provide a
list of those computational interfaces and operations or streams that corre-
spond to the enterprise interaction, together with a statement of whether this
correspondence applies to all occurrences of the interaction, or is qualified by
a predicate. It is then up to the specifier to apply these rules and, in doing
so, generate a set of domain-specific correspondences.
7.4 Anatomy of a Correspondence Specification
The UML4ODP standard brings all this together by defining a metamodel
for correspondence specifications. This is outlined in figure 7.2. The specifi-
cation itself is a separate model, linked to the viewpoint models but standing
outside of all of them.
The two viewpoints characterize the specification that is to tie them to-
gether. The specification itself is built up from a set of correspondence
rules, members of which are referred to from a set of correspondence links.
Every correspondence link has two correspondence endpoints, which are
each associated with some set of terms in the viewpoint concerned.
The element Term in this metamodel can be associated with any language
element in the viewpoint concerned. In the UML profile, this is done by
the use of tags, so that there is no commitment to the properties of the
namespaces concerned; this results in the minimum of impact on the writers
of the viewpoint specifications.
Correspondence rules express constraints that must be enforced for the
set of elements from the two viewpoints being linked.
One example is the
