Information Technology Reference
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Class Department
attribute Dept#: integer
attribute Dept-name: string
association attribute hire ref set(Instructor)
Method
Create Department
end Department
Class Instructor
attribute Inst-name: string
attribute Inst-addr: string
association attribute hired-by ref Department
Method
Create Instructor
end Instructor.
In this example, class Department has a complex attribute Instructor such that the
attributes and the methods of an independent class Instructor are contained in the
class Department. The data structure of the object-oriented schema can be illus-
trated in Fig.
2.7
where the class defining and object is used to find the code for the
method that is applied to the object (Date
1995
).
In an object-oriented schema, a special relationship between an instance of a
subclass and the instances of the deep extent of a class exists. Such a relationship
can be represented by a “class instance inclusion dependence” indicating that the
class instances of a subclass is a subset of the class instances of its superclass. In
other words, every instance value of a subclass, is also an instance value of its su-
perclass. However, for every instance value of a superclass, there may not be any
subclass object. Thus, the isa relationship can be described as an inclusion depen-
dency (ID) in an object-oriented schema as follows:
ID: subclass object OID ↆ All superclass object OID
(Note: “All” refers to the deep extent of the class).
This can be illustrated in Fig.
2.8
.
2.4.1
Unified Model Language (UML)
To describe the semantic of the object-oriented database, we use an object-oriented
conceptual model such as UML, which is popular in object-oriented system design.
In general, UML is more powerful than the EER model because UML includes not
only static data but also dynamic data behavior in its method. The syntax of UML
can be described as follows (Booch
1994
):
• Class—Eachrectangularboxisaclass.Forexample,inFig.
2.9
Patient is a
class.
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