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Презентация на тему Analysis and Design of Data Systems. Enhanced ER (EER) Mode. (Lecture 11)

The EER model includes all the modeling concepts of the ER modelEnhanced ER (EER) Model
IE301 Analysis and Design of Data Systems  Lecture 11 Enhanced ER (EER) ModelAram Keryan The EER model includes all the modeling concepts of the ER modelEnhanced ER (EER) Model An entity type can have numerous subgrupings that need to be represented Subclasses and Superclassessubclasssuperclass SpecializationSpecialization is the process of defining a set of subclasses of an Each entity that is a member of a subclass can also be Specific attributeSpecific relationshipFeatures of Subclasses Reasons for including class/subclass relationships and specializations in a data model:Certain attributes GeneralizationGeneralization is a reverse process to Specialization Generalization Constraints on Specializations By placing a condition on the value of some attribute of the If all subclasses in a specialization have their membership condition on the Disjointness constraint specifies that an entity can be a member of at If the subclasses are not constrained to be disjoint, their sets of A total specialization constraint specifies that every entity in the superclass must Shared sublassesA subclass with more than one superclasses is called a shared Specialization  Hierarchies UNION SubclassesShared SubclassVSUnion SubclassSuperclasses must all have the same keySuperclasses can have different keys UNION SubclassesENGINEERING_MANAGER is a subclass of each of the three superclasses ENGINEER, A Union Subclass can be total or partial. A total category holds
Слайды презентации

Слайд 2 The EER model includes all the modeling concepts

The EER model includes all the modeling concepts of the ER modelEnhanced ER (EER) Model

of the ER model
Enhanced ER (EER) Model


Слайд 3 An entity type can have numerous subgrupings that

An entity type can have numerous subgrupings that need to be

need to be represented explicitly because of their significance:
Subclasses

and Superclasses

superclass

Each of these subgrupings is called a subclass

subclass

Each entity that is a member of a subclass is also an entity of a corresponding superclass (secretary is also an employee)
It is not necessary that every entity in a superclass is a member of some subclass


Слайд 4 Subclasses and Superclasses
subclass
superclass

Subclasses and Superclassessubclasssuperclass

Слайд 5 Specialization
Specialization is the process of defining a set

SpecializationSpecialization is the process of defining a set of subclasses of

of subclasses of an entity type
The set of subclasses

that forms a specialization is defined on the basis of some distinguishing characteristic of the entities in the superclass

Based on the job type

Based on the method of pay


Слайд 6 Each entity that is a member of a

Each entity that is a member of a subclass can also

subclass can also be a member of another subclass

(salaried employee who is also an engineer belongs to the two subclasses ENGINEER and SALARIED_EMPLOYEE of the EMPLOYEE entity type)

Entity that is a member of a subclass inherits all the attributes of the entity as a member of the superclass

Entity that is a member of a subclass also inherits all the relationships in which the superclass participates

More on Subclasses and Superclasses


Слайд 7 Specific attribute
Specific relationship
Features of Subclasses

Specific attributeSpecific relationshipFeatures of Subclasses

Слайд 8 Reasons for including class/subclass relationships and specializations in

Reasons for including class/subclass relationships and specializations in a data model:Certain

a data model:
Certain attributes may apply to some but

not all entities of the superclass
Some relationship types may be participated in only by entities that are members of the subclass.

Specialization process allows us to do the following:

Define a set of subclasses of an entity type
Establish additional specific attributes with each subclass
Establish additional specific relationship types between each subclass and other entity types or other subclasses


Слайд 9 Generalization
Generalization is a reverse process to Specialization

GeneralizationGeneralization is a reverse process to Specialization

Слайд 10 Generalization

Generalization

Слайд 11 Constraints on Specializations

Constraints on Specializations

Слайд 12 By placing a condition on the value of

By placing a condition on the value of some attribute of

some attribute of the superclass we can determine exactly

the entities that will become members of each subclass. Such subclasses are called
predicate-defined subclasses.


OTHER


Defining predicate


Слайд 13 If all subclasses in a specialization have their

If all subclasses in a specialization have their membership condition on

membership condition on the same attribute of the superclass,

the specialization itself is called an attribute-defined specialization

Defining attribute

When we do not have a condition for determining membership in a subclass, the subclass is called user-defined


Слайд 14 Disjointness constraint specifies that an entity can be

Disjointness constraint specifies that an entity can be a member of

a member of at most one of the subclasses

of the specialization.

A specialization that is attribute-defined implies the disjointness constraint
Disjointness also applies to user-defined subclasses of a specialization


Слайд 15 If the subclasses are not constrained to be

If the subclasses are not constrained to be disjoint, their sets

disjoint, their sets of entities may be overlapping
that is,

the same (real-world) entity may be a member of more than one subclass of the specialization

Слайд 16 A total specialization constraint specifies that every entity

A total specialization constraint specifies that every entity in the superclass

in the superclass must be a member of at

least one subclass in the specialization

partial specialization allows an entity not to belong to any of the subclasses

Total

Partial


Слайд 17 Shared sublasses

A subclass with more than one superclasses

Shared sublassesA subclass with more than one superclasses is called a

is called a shared subclass
Shared sublcasses inherit attributes and

relationships from multiple classes. That concept is known as multiple inheritance



Слайд 18
Specialization Hierarchies

Specialization Hierarchies

Слайд 19 UNION Subclasses
Shared Subclass
VS
Union Subclass
Superclasses must all have the

UNION SubclassesShared SubclassVSUnion SubclassSuperclasses must all have the same keySuperclasses can have different keys

same key
Superclasses can have different keys


Слайд 20 UNION Subclasses
ENGINEERING_MANAGER is a subclass of each of

UNION SubclassesENGINEERING_MANAGER is a subclass of each of the three superclasses

the three superclasses ENGINEER, MANAGER, and SALARIED_EMPLOYEE, so an

entity that is a member of ENGINEERING_MANAGER must exist in all three.
This represents the constraint that an engineering manager must be an ENGINEER, a MANAGER, and a SALARIED_EMPLOYEE simultaneously;
that is, ENGINEERING_MANAGER is a subset of the intersection of the three classes (sets of entities).
Shared subclass such as ENGINEERING_MANAGER inherits all the attributes of its superclasses SALARIED_EMPLOYEE, ENGINEER, and MANAGER

Union subclass is a subset of the union of its superclasses. Hence, an entity that is a member of OWNER must exist in only one of the superclasses. This represents the constraint that an OWNER may be a COMPANY, a BANK, or a PERSON.
Union subclass such as OWNER entity inherits the attributes of a COMPANY, a PERSON, or a BANK, depending on the superclass to which the entity belongs.


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