Schema Translation - Information Systems Reengineering, Integration and Normalization - page 105

Table 3.1 Derive semantics from IDs

Given derived inclusion
dependency

Derived Semantics

Instructor.Dept#
Department.Dept#

n:1 relationship between entities
Instructor and Department

Section.Dept#
Department.Dept#
Section.Inst_name
Instructor.Inst_name
Section.Course#
Course.Course#

1:n relationship between entities
Instructor and Section and between
Course and Section.

Grade.Dept#
Section.Dept#
Grade.Inst_name
Section.Inst_name
Grade.Course#
Section.Course#
Grade.Student#
Student.Student#

m:n relationship between

relationship Section and entity

Student.

Prerequisite.Course#
Course.Course#

1:1 relationship between Course
and Prerequisite

and pointers. When constrained by cardinality, appropriate symbols must be speci-
fied by a line (link) with or without a solid dot sign. For example, the 1:n relation-
ship in Fig. 3.34 can be mapped into the UML where “Cour-prer” is an association
between the classes and Prerequisite.
Step 3—Map generalization to method
For generalization, the variances among entities are suppressed and their com-
monalities are identified by generalizing them into one single class. The original
entities with each of its unique differences are special subclass(es). The mutually
exclusive subclass(es) are called disjoint generalization. The mutually inclusive
subclasses are called overlap generalization. For example, disjoint generalization
in Fig. 3.35 can be mapped into the UML where subclass(es) Contract-Staff and
Permanent-Staff inherit the properties and operations of superclass Staff. The map-
ping of overlap generalization into the object-oriented schema is similar to the map-
ping of disjoint generalization into the object-oriented schema except that the check
statement is omitted and a solid triangle is used to indicate overlapped subclass(es).
Step 4—Map categorization to “multiple” inheritance.
A categorization is derived by mapping isa relationships and their record types
to a superclass/subclass such that a set of superclass(es) can be united to form a
superclass. All these superclass(es) may have different key attributes as they are
originally independent classes. For example, the categorization in Fig. 3.36 can
be mapped into the following UML model where the subclass Research-Assistant
comes from one of the two superclass(es): Faculty or Graduate Student.