The document covers the fundamentals of enhanced entity-relationship and object modeling, focusing on concepts such as subclass, superclass, specialization, generalization, and inheritance. It explains how subclasses are subsets of entities in a superclass and outlines the processes of specialization and generalization. Additionally, it addresses constraints such as disjointness and completeness in specialization/generalization relationships.

1. Fundamentals of database
HARAMBE UNIVERSITY
COLLAGE OF COMPUTING
COMPUTER SCINCE DEPARTMENT
Chapter 4: Enhanced Entity –Relationship and Object modeling
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2. Lesson Outline
 Subclass,
 Super-class and Inheritance
 Specialization
 Generalization
 Constraints and Characteristics of Specialization and
Generalization
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3. Cont…
Subclass
Class: Set or collection of entities
Subclass is Class whose entities must always be a subset
of the entities in another class
 An entity type may have additional meaningful sub
groupings of its entities
• Example: student may be further grouped into:
Regular student, extension student, summer student
Undergraduate student, master student, PHD
student
 EER diagrams extend ER diagrams to represent these
additional sub groupings, called subclasses or subtypes
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4. Cont…
 Each of these sub groupings is a subset of student entities
 Each is called a subclass of student
o These are also called IS-A/IS-AN relationships
i.e. Regular student IS-A student, summer student IS-A
student).
 Super class - Is the term used to describe the Entity that
contains a subclass(s). Student is the super class for each
of these subclasses
 These are called super class/subclass relationships:
 student/regular student
 student/extention student
 student/summar
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5. Cont…
Generalization, Specialization, and Inheritance
1.Specialization
Is a process of defining a set of subclasses of an entity
type, this entity type is called supper class of entity type.
It is a top-down conceptual refinement process
Example: the set of subclass (regular student, summer
student, extension student) is a specialization of the
supper class student.
2.Generalization
Generalization derives from the fact that the super class
generalizes the subclasses. making generalization by
standing from the subclass into single supper
class/process of defining a generalized entity type.
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6. Cont…
Example: all regular students, summer students and
extension students are subclasses of the generalized
supper class student.
Inheritance
Is the mechanism for sharing attributes, operations, and
associations via the generalization/specialization
relationship.
Example:
 Masters student share some attribute from student,
 Regular student share some attribute from supper class
student,
 Summer student share some attribute from student.
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7. Cont…
Constraints of Specialization and Generalization
• If we can determine exactly those entities that will become
members of each subclass by a condition, the subclasses are
called predicate-defined (or condition-defined) subclasses
o Condition is a constraint that determines subclass
members
o Display a predicate-defined subclass by writing the
predicate condition next to the line attaching the subclass
to its super class
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8. Cont…
• If all subclasses in a specialization have membership
condition on same attribute of the super class,
specialization is called an attribute-defined
specialization.
Attribute is called the defining attribute of the
specialization
Example: Job Type is the defining attribute of the
specialization {SECRETARY, TECHNICIAN,
ENGINEER} of EMPLOYEE
NB: job type same with student type
• If no condition determines membership, the subclass is
called user-defined
– Membership in a subclass is determined by the
database users by applying an operation to add an
entity to the subclass
– Membership in the subclass is specified individually
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9. Cont…
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10. Cont…
Two basic constraints can apply to a
specialization/generalization:
– Disjointness Constraint:
– Completeness Constraint:
• Disjointness Constraint: Specifies that the subclasses
of the specialization must be disjoint:
• meaning-an entity can be a member of at most one of the
subclasses of the specialization
– Specified by d in EER diagram
– If not disjoint, specialization is overlapping: meaning -
the same entity may be a member of more than one
subclass of the specialization
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11. Cont…
employee
Student
job
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12. Cont…
• Completeness Constraint:
– Total specifies that every entity in the superclass must
be a member of some subclass in the
specialization/generalization
– Shown in EER diagrams by a double line
– Partial allows an entity not to belong to any of the
subclasses
– Shown in EER diagrams by a single line
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13. THANK YOU
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