Database and Expert Systems Integration - Information Systems Reengineering, Integration and Normalization - page 315

Fig. 8.6 An example of a
method in the frame model
metadata

Object Identifier: Hector_Credit_Rating
Attributes:
Customer= "Hector"
Customer-Status= "House-Owner"
Credit-Rating= Method(credit-rating)
Methods:
credit-rating (): Text;
{ IF Customer-Status = "House-Owner"
Then Credit-Rating = "Good"}

structuring and sharing not only data, but also the programs (i.e., methods) that act
on the data. The frame model metadata uses this characteristic to integrate rules
into its model. The methods of the frame model metadata represent the behavior,
the active rules, and the deductive rules of a particular object. Since the behavior
representation of the object-oriented model is reflected by the different needs of
different user communities, there is not an established way of representing behavior
in object-oriented systems. The method body takes a production rule structure in
the frame model metadata. Figure 8.6 is an example of a method of the object Hec-
tor_Credit_Rating.

• Constraints

There are many properties of data that cannot be captured in the form of structures.
These properties essentially serve as additional restrictions on the values of the
data and/or how the data may be related (structured). For example, there may be
a restriction that if a person is head of a department, the person must also belong
to the department. Such restrictions cannot be expressed in terms of structures, but
must be captured by some additional mechanism. It is a primary consideration of
database technology to ensure data (or knowledge) correctness and consistency.
This requires the system to support integrity constraint functions. These functions
are also required to allow proper handling of updates of knowledge for interrelated
actions and active database rules. There are many semantics present in constraints
that can be very useful when answering queries. Constraints can be used to prevent
a possibly expensive database search operation or to answer otherwise unsolvable
queries (Houstsma and Apers 1990 ). The constraint technology used in current da-
tabase systems requires different levels of integrity constraint. There are two types
of constraints used in database technology:

1. Static constraints that limits the allowable database states so as to accurately
reflect the real world situation.
2. Dynamic constraints that restrict the possible database state transitions.

For example, we can define an attribute constraint in the attribute salary. The con-
straint will be:

(salary_refuse ( ) Self Insert Before ( ) )