Databases Reference
In-Depth Information
entity
instances.
Entities
can
form
a
hierarchy
of
generalizations
or
aggregations.
13.3.2
Conceptual Modeling Tools
Conceptual design tools are those which support concept discovery, the
organization of concepts into a coherent schema, and the validation of the
schema with respect to user requirements. This section addresses three kinds
of tools: those that help in the creative design done by the user, those that
help in abstracting the conceptual schema from existing files and DBs, and
those that derive conceptual schemas from natural language sentences.
13.3.2.1 Creative Design
Creative design is a modeling activity that starts from scratch or, more
precisely, from the informal knowledge a designer has in mind. Every con-
ceptual entity and relationship is abstracted directly from the designers
perception of the real world. Actually, many DB schemas are designed that
way. The designer translates users needs into the conceptual language used
to formalize those needs.
CASE tools required by creative design are simple, but they must also
be attractive. They are limited to a graphical interface that supports the
conceptual model and a data dictionary to store the resulting schemas.
The success of the interface is obviously related to its friendliness, ease
of use, and semantic expressiveness. Friendliness is related to the graphical
widgets used to represent the concepts of the conceptual model. It is rec-
ommended that the designer use either standard or well-accepted representa-
tions or metaphors that do not give rise to confusion and misunderstanding.
Ease of use means providing an interface that can be manipulated by intui-
tion and that conforms to the most popular actions used in Office Works
and other successful products. Semantic expressiveness depends on the con-
ceptual model used. A rich semantic model reduces the gap between a per-
ception and its formal representation and allows easy capture of the meaning
of the real world considered. A poor conceptual model requires many more
skills in the design because it often leads to a reformulation of the perception
into more basic facts that can be expressed in the conceptual model.
Although creative design is based on the use of some diagrammatic
interface, it requires minimal support in terms of syntactic and semantic veri-
fications. An attractive graphical interface should implement procedures that
enforce the structuring rules of the model. For example, in the E/R model,
relationships do not link other relationships but entities; there are no cycles
