Databases Reference
In-Depth Information
This section develops that line of reasoning. Along the way, we intro-
duce informally the terminology and give an intuitive idea of the basic
concepts.
2.2.1
Conceptual Schema of the State
The objective of the memory function of an IS is to maintain a consistent
representation of the state of its domain. The state of a domain consists of a
set of relevant properties.
The question of which exactly are the relevant properties of the domain
of an IS depends on the purpose for which the IS is built. We have already
mentioned that an IS is always a means for a wider system to achieve its
objectives. The relevant properties are determined by the functions of those
objectives and of the expected contribution of the IS to them. We focus
here on what are relevant properties rather than how to determine them.
That, of course, does not mean that the latter aspect is less important than
the former one.
In the IS field, we make the fundamental assumption that a domain
consists of objects and the relationships between those objects, which are
classified into concepts. The state of a particular domain, at a given time,
consists, then, of a set of objects, a set of relationships, and a set of concepts
into which those objects and relationships are classified. For example, in the
domain of a company, we may have the concepts of Customer, Product, and
Sale. Those concepts are usually stable. On the other hand, at a given instant,
we have objects classified as customers, objects classified as products, and
relationships between customers and products classified as sales.
That fundamental assumption is also shared by disciplines such as
linguistics, (first-order) logic, and cognitive science. Unfortunately, those
disciplines have not yet arrived at an agreement in the terminology, the defi-
nitions, the concepts, and the mechanisms to distinguish among objects and
relationships in a domain. The result is that we do not have at our disposal a
solid theoretical basis, and, as is often the case in the IS field, we must adopt a
humble and eclectic attitude.
The assumption that a domain consists of objects, relationships, and
concepts is a specific way to view the world (domain). At first sight, it seems
an evident assumption. Reality, however, is far from that. Other views are
possible, views that may be more adequate in other fields. As a simple and
well-known example in propositional logic, one assumes that domains con-
sist of facts, which may be either true or false. The study of the nature and
