Databases Reference
In-Depth Information
13.3.3
Verification and Validation Tools
This section deals with the properties of a good conceptual schema and
shows how CASE tools support the verification of these properties. We can
divide the desired properties into three categories: (a) formal properties,
(b) quality factors, and (c) conformance with user needs. With respect to for-
mal properties, a good conceptual schema has to be consistent, complete, and
irredundant, if it is to give birth to a sound DB. With respect to quality, a
conceptual schema has to be understandable and able to evolve wherever the
analysis progresses. With respect to the user needs, a conceptual schema has
to conform to the requirements, that is, represent exactly what the user wants
to represent. The following subsections illustrate how CASE tools contribute
to the assessment of those desired properties and how far one can go in the
identification of those properties.
13.3.3.1 Formal Verification
As stated earlier, a good conceptual schema has to be intrinsically correct,
that is, consistent, complete, and irredundant. Depending on the conceptual
model used, these properties may vary from one model to another. Conse-
quently, the following desired list of properties is not exhaustive and applies
to the extended E/R model described in Figure 13.4.
Schema Consistency
Consistency is defined with respect to both the syntactic rules of the concep-
tual model and the semantic rules. A schema is syntactically consistent if it
satisfies the construction rules of the model. With respect to our conceptual
model, an instance of this model is syntactically consistent if it satisfies the
following properties:
The names of entities and relationships are distinct, that is, there is
unicity of names.
·
None of the attributes, entities, and relationships can exist inde-
pendently in the schema without characterizing or being related to
the others. This property is called nonisolation of concepts.
·
A relationship is at least a binary relationship between not necessar-
ily distinct entities.
·
A given relationship does not participate in another relationship.
·
