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and, together with the nonfunctional requirement specification, corresponds
to the system specification.
During requirements validation, specifications are checked with respect
to users needs. In this phase, it must be ensured that users get a complete
understanding of how the future system will be before it is built. This is
also a crucial phase that can be done well only if requirements have been
described explicitly.
Validation can be performed in two main ways:
By presenting the conceptual schema and in general the specifica-
tions in a language and form that is easily understood by users. If the
conceptual modeling language used is not completely understand-
able by the users, it will be necessary to provide either some help
for its interpretation or translation to more familiar languages (not
excluding natural language). When the conceptual schema is large,
as is often the case, its structuring in fragments or views may be
mandatory.
·
By building (partial) prototypes of the system. If the conceptual
modeling language used is formal, then prototypes may be generated
automatically. This form of validation is usually more effective than
the other form, but in general it is more expensive.
·
In summary, conceptual schemas are elaborated during the require-
ments engineering stage and are the basis for the next stage, system design.
For further details on how these activities can be facilitated by comput-
ers, see Chapter 13.
2.5
Desirable Properties of Conceptual Schemas
Now that we have seen what the conceptual schemas are and their role in the
architecture of the system and during the development process, this section
describes which properties should have these schemas in order to play those
roles effectively [1517].
A well-known property of conceptual schemas is the 100% principle,or
completeness, which states that
All relevant general static and dynamic aspects, i.e., all rules, laws, etc.,
of the universe of discourse should be described in the conceptual
