Databases Reference
In-Depth Information
13.3.5 Conceptual Design Based Upon Reusable Components
Object-oriented methods recommend the reuse of existing components in
the design of new systems. Translated in the context of DB design and
in contrast to the classical design approach in which a conceptual schema
is constructed directly from user requirements or from legacy systems, reuse
implies that the designer must endeavor to construct a conceptual schema
mainly from existing elements. There is a difference between design by reuse
and design by integration. In design by integration, all the integrated sche-
mas concern the same real-world application, while design by reuse means
customization of elements that have been designed for different purposes.
A simple example that highlights this difference is illustrated by a con-
ceptual schema devoted to flight booking that can be reused in train booking
or hotel booking. Another example concerns a conceptual schema designed
for the management of a specific conference (paper reception, participant
registration, reviewer assignment, evaluation synthesis, and program schedul-
ing) that can be reused for another conference that does not necessarily have
the same organizational rules (different number of reviewers, different
evaluation systems, different organization of the final program). Designing
by reuse means searching for one or several schemas that have similar pur-
poses but not necessarily in the same application domain as the one
addressed in the given application, customizing those schemas to adapt them
to the given application, and possibly integrating them when there are several
to have one unique global schema. We can summarize the reuse process into
three steps: (1) searching, (2) customizing, and (3) integrating. While the
third step is the same as design by schema integration, the first two steps are
specific to design by reuse.
The first task in design by reuse is to investigate and select those ele-
ments that best match the modeling purpose, according to the given applica-
tion requirements. Then the selected building blocks are retouched and
customized by changing the names of concepts, removing or adding some
concepts, changing some relationship roles and cardinalities, changing
some attribute domains, and so forth.
Retrieval mechanisms of reusable components usually follow one of
two methods: browsing or querying. Although it is more interesting to
browse a reasonably sized repository of objects, it quickly becomes a time-
consuming and burdensome task with an increasing number of resulting
schemas. Reference [22] has proposed a flexible language that combines que-
rying and browsing. The proposed retrieval solution has two main character-
istics: It permits imprecise querying, and it deals with the semantics (concept
