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conceptualization such that its entities and relationships are represented in
the IS.
2.2.2 Information Base
An information base is a description of the entities and relationships of a
domain that are represented in the IS [10]. In principle, this description
could be done in any language, but usually it is done in a logic-based lan-
guage. Sometimes, the description of an entity or a relationship is called a
fact, and we say that the information base contains the facts about a domain.
For example, if we use the language of first-order logic as the modeling
language, we could have a schema formed by predicates Person, Book, and
Reads, which represent entity types Person and Book and relationship type
Reads. The information base might contain, at some time, the facts Per-
son(A), Book(B), and Reads(A,B).
Figure 2.4 illustrates the relationship between a conceptual schema and
an information base. The conceptual schema of the domain includes the
concepts from Figure 2.3 and two other concepts, Town and Lives. However,
we want to represent in the IS only the entities and relationships shown in
the conceptual schema of Figure 2.3. The conceptual schema is described in
a graphical language, in which rectangles correspond to entity types and lines
to relationship types. The information base contains three facts, described in
the language of first-order logic. Predicates correspond to entity and relation-
ship types.
The information base does not exist physically. It is only an abstract
description we use to reason about a schema and to exemplify particular
situations
in
a
domain.
Naturally,
the
IS
must
maintain
an
internal
Conceptual schema of the domain
Conceptual schema of
the information system
reads
Town
Lives
Person
Reads
Book
Person
Book
Person (A)
Book (B)
Reads (A,B)
domain
Information base
Figure 2.4
Conceptual schema and information base.
