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ER & Enhanced ER & Enhanced Entity RelationshipEntity Relationship

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Learning Objectives

• MAPPING• ER MODEL

– Weak entity sets– Aggregation

• EER (Enhanced /Extended Entity Relationship)– Superclass/subclass relationships

• Shared SubclassShared Subclass– GeneralizationGeneralization– SpecializationSpecialization

• Specialization HierarchySpecialization Hierarchy• Specialization LatticeSpecialization Lattice

– Attribute InheritanceAttribute Inheritance– Etc

MAPPINGMAPPING

FIGURE 1Ternary relationship types. (a) The SUPPLY relationship.

FIGURE 2Mapping the n-ary relationship type SUPPLY from Figure 1

Summary of Mapping constructs and constraints

Table 1.1 Correspondence between ER and Relational Models

ER Model Relational ModelEntity type “Entity” relation1:1 or 1:N relationship type Foreign key (or “relationship” relation)M:N relationship type “Relationship” relation and two foreign keysn-ary relationship type “Relationship” relation and n foreign keysSimple attribute AttributeComposite attribute Set of simple component attributesMultivalued attribute Relation and foreign keyValue set DomainKey attribute Primary (or secondary) key

Weak Entity Sets

• Entity sets that do not have sufficient attributes to form a key are called weak entity sets.

• A weak entity set existentially depend upon (one or more) strong entity sets via a one-to-many relationship from whom they derive their key

• A weak entity set may have a discriminator (or a partial key) that distinguish between weak entities related to the same strong entity

• key of weak entity set = Key of owner entity set(s) + discriminator

Weak Entity Sets

• Adalah set entitas yang tidak memiliki atribut kunci (key attributes)yang cukup.

• Entias lemah ini bergantung kepada satu atau lebih entitas kuat menggunakan hubungan one-to-many

• Suatu set entitas lemah memiliki kunci yang biasa disebut diskriminator. Fungsinya ?

• Kunci dari set entitas = kunci dari entitas kuat yang berhubungan + diskriminator

Weak Entity Sets

• The existence of a weak entity set depends on the existence of an identifying entity set.– it must relate to the identifying entity set via a total, one-to-

many relationship set from the identifying to the weak entity set.

– Identifying relationship depicted using a double diamond.• The discriminator (or partial key) of a weak entity set is the set of

attributes that distinguishes among all the entities of a weak entity set.

• The primary key of a weak entity set is formed by the primary key of the strong entity set on which the weak entity set is existence dependent, plus the weak entity set’s discriminator.

Weak Entity Sets

• Keberadaan set entitas lemah tergantung dari set entitas kuatnya.– Gambar hubungannya dapat diidentifikasi dengan dobel

diamond.• Diskriminator dari set entitas lemah adalah kumpulan atribut

yang membedakan entitas yang ada dalam entitas lemah.• Primary key dari entitas lebah dibentuk dari primary key set

entitas kuat ditambahkan dengan diskriminator.

Weak Entity Sets (cont.)

customer custacct account

cust name

Cust no

street

city

acct number balance

opening date

transaction

Trans#

log

• Transaction is a weak entity set related to accounts via log relationship.

• Trans# distinguish different transactions on same account

A Chain of Weak Entity Sets

• Names of state are unique and form the key.• Names of city are unique only within a state

(e.g., 24 Springfield’s within the 50 states).• Names of streets are unique within a city.

Multiple cities could have streets with the same name.

city state

street

Example illustrating that a weak entity set might itself participate as owner in an identifying relationship with another weak entity set.

Located in

Located in

A Weak Entity Set with Multiple Owner Entity Sets

• Reviewers review movie and assign a rating -- thumb up/thumbs down.

• Review is a weak entity set whose owner sets correspond to both the movie and the reviewer entity sets.

• Key for the review entity set = key of movie + key of reviewer

review

movie

reviewerrating

title

name

Weak Entity Sets (Cont.)

• Double rectangles represent weak entity sets.

• Discriminator of a weak entity set underlined with a dashed line.

• payment-number – discriminator of the payment entity set

• Primary key for payment – (loan-number, payment-number)

Weak Entity Sets (Cont.)

• Note: the primary key of the identifying entity set is not explicitly stored with the weak entity set, since it is implicit in the identifying relationship.

• If loan-number were explicitly stored, payment could be made a strong entity, but then the relationship between payment and loan would be duplicated by an implicit relationship defined by the attribute loan-number common to payment and loan.

employeeproject

tools

works_using

employee project

tools

work

usingrelationships among relationships not permitted in ER!

incorrect since it requires each project to use tools

Limitations of ER Model

We wish to represent that an employee works on a specific project possibly using multiple tools

employee project

tools

works

using

N

Aggregation

N

• Treat the relationship set work and the entity sets employee and projects as a higher level entity set-- an aggregate entity set

• Permit relationships between aggregate entity sets and other entity sets

ER to Relational

• Aggregation: Relationship will be mapped to a table,; extended with p.k. of participating entity set(s) + relationship + its own attributes ( if exists)

• Example:

Company Job-Applicant

Job-Offer

Interview

Results-In

P.K(JOB_OFFER) P.K(INTERVIEW)RESULTS_IN

M N

EEREER(Enhanced Entity (Enhanced Entity

Relationsip)Relationsip)

Sub-ClassSub-Class Shared Subclass Shared Subclass

Super-ClassSuper-ClassGeneralizationGeneralizationSpecializationSpecialization

Specialization HierarchySpecialization HierarchySpecialization LatticeSpecialization LatticeAttribute InheritanceAttribute Inheritance

Summary of Symbols Used in E-R Notation

Summary of Symbols (Cont.)

Subclass

• Entity type describes:– Type of entity– The entity set

• Example: ‘EMPLOYEE’• Employee can be sub-grouped into:

– Secretary– Engineer– Technician– Manager

• These are called the subclass of EMPLOYEE entity type.

Pengertian Subclass (EER)

Sub-Kelas (Subclass) •Subset dari suatu entitas yang dikelompokkan dalam pengertian tertentu yang perlu disajikan secara eksplisit.•Contoh : Entitas PEGAWAI mempunyai beberapa subclass seperti SEKRETARIS, TEKNISI, AHLI (Gbr. 1 Spesialisasi tipe pekerjaan entity PEGAWAI)

Super-class

• EMPLOYEE entity type is the super class of engineer, secretary & technician class

• Subclass represent the same mini-world entity of the superclass, but in a distinct specific role.

• These are also called IS-A relationships (SECRETARY IS-A EMPLOYEE, TECHNICIAN IS-A EMPLOYEE, …).

• Entity in a subclass must be a member of a superclass, but not vice-versa! Example…?

!

Pengertian SuperclassSuper-Kelas (Superclass) •Entitas yang merupakan induk dari subclass-subclassnya.•Contoh : Subclass SEKRETARIS, TEKNISI, SALES mempunyai superclass PEGAWAI (Gbr. 1)

Spesialisasi (Spesialiazation) •Proses pemecahan entitas menjadi subclass-subclass beserta atribut-atributnya.•Terdapat beberapa jenis spesialisasi seperti Disjoint Total, Disjoint Partial, Overlapping Total dan Overlapping Partial.•Contoh : Spesialisasi dari PEGAWAI berdasarkan tipe pekerjaan.

EER

• EER = ER + Generalisasi + Spesialisasi + Kategorisasi• Superclass := set entitas yang umum dan memiliki relasi

satu atau lebih subclass• Subclass := adalah sub-sub kelompok dari entitas yang

berguna bagi organisasi. Subclass merupakan spesialisasi dari entitas superclass. Subclass mewarisi atribut dan relasi yang berkaitan dengan superclassnya.

Type inheritance

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

• It also inherits all relationships

Specialization

• Is a process of defining a set of subclasses of an entity type (the superclass)

• Secretary, engineers, & technician are specialization of EMPLOYEE based on job type attribute

Spesialisasi (Spesialiazation)

• Proses pemecahan entitas menjadi subclass-subclass beserta atribut-atributnya.

• Terdapat beberapa jenis spesialisasi seperti Disjoint Total, Disjoint Partial, Overlapping Total dan Overlapping Partial.

• Contoh : Spesialisasi dari PEGAWAI berdasarkan tipe pekerjaan.

Cont’d

• May have several specialization based on different characteristics

• Example, EMPLOYEE can be subclass-ed into Salaried_Employee and Hourly_Employee

Benefit of Specialization

• 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

• Refer to the EER diagram…!

Specialization Example

Subclass/Superclass Relationshipsaccount

ISA

savings checking

account

balance

interest rates overdraft amount

• savings and checking are subclasses of the account entity set

• account is a superclass of savings and checking entity sets

• An entity in a subclass has to belong to superclass as well -- that is, every savings account is also an account. Similarly every checking account is also an account

• Attribute Inheritance: subclasses inherit all the attributes of the superclass. Similarly, subclasses inherit all relationships in which the superclass participates

Constraints in Supertype/ Subtype Relationships

• Completeness Constraints: Whether an instance of a supertype must also be a member of at least one subtype.– Total Specialization Rule: Yes (Fig. 4-6a -

note the double line convention)– Partial Specialization Rule: No (Fig. 4-6b -

single line convention)

Figure 4-6a – Examples of completeness constraints

Total specialization rule

A patient must be either an outpatient or a resident patient (at least one)

Figure 4-6b – Partial specialization rule

A vehicle could be a car, a truck, or neither

Constraints in Supertype/ Disjointness constraint

• Disjointness Constraints: Whether an instance of a supertype may simultaneously be a member of two (or more) subtypes.– Disjoint Rule: An instance of the supertype

can be only ONE of the subtypes– Overlap Rule: An instance of the supertype

could be more than one of the subtypes

(a) Disjoint rule

Figure 4-7 – Examples of disjointness constraints

A patient can either be outpatient or resident, but not both

Figure 4-7(b) Overlap rule

A part may be both purchased and manufactured

UML Class Diagram Notation (Cont.)

*Note reversal of position in cardinality constraint depiction

Notations from the EER diagram

• Subset symbol • Specific attributes, or local attributes• Specific relationships• Superclass/subclass

EMPLOYEE/Secretary resembles 1:1 relationship at the instance level, of one entity.

Disjoint,Overlap?Partial,Total ?

FIGURE 4.4EER diagram notation for an attribute-defined specialization on JobType.

d

FIGURE 7.4Options for mapping specialization or generalization. (a) Mapping the EER schema in Figure 4.4 using option 8A.

FIGURE 7.4Options for mapping specialization or generalization. (c) Mapping the EER schema in Figure 4.4 using option 8C.

FIGURE 4.5EER diagram notation for an overlapping (nondisjoint) specialization.

o

FIGURE 7.4Options for mapping specialization or generalization. (d) Mapping Figure 4.5 using option 8D with Boolean type fields Mflag and Pflag.

Generalization

• Identify common features (attributes), and generalize into a superclass

• Example: truck & car can be generalized into VEHICLE

• Inverse of the specialization process

Generalisasi

• Generalisasi adalah proses bottom-up dalam mendefinisikan dan melakukan generalisasi terhadap beberapa subclass menjadi satu entitas superclass.

• Generalisasi merupakan proses untuk minimalisasi perbedaan antar entitas dengan mendefinisikan atribut yang sama.

FIGURE 4.3Generalization. (b) Generalizing CAR and TRUCK into the superclass VEHICLE.

FIGURE 7.4Options for mapping specialization or generalization. (b) Mapping the EER schema in Figure 4.3b using option 8B.

Predicate defined subclasses

• Also called condition-defined subclasses

• Conditioned by a defining predicate at the superclass

• Example, JobType = ‘Secretary’• Place attribute name on the arc

Rules & Pemahaman !

Rules & Pemahaman!

User defined subclass

• Membership is specified individually for each entity by the user

• Not by any condition that may be evaluated automatically

• Example: Manager subclass

Rules & Pemahaman !

Disjointness constraints

• Subclasses of a specialization must be disjoint

• An entity can only be at most one of the subclass

• Look at the EER diagram• Use (d)

Rules & Pemahaman !

Overlap

• The same entity may be a member of more than one subclass of the specialization

• Use the (o)• Example, a person can be:

– A student– A faculty member– An alumni

Rules & Pemahaman !

Rules & Pemahaman !

Completeness constraints

• Total specialization:– Every entity in the superclass must be a

member of some subclass– Example, the Salaried_Employee and

Hourly_Employee– Shown using double line

Rules & Pemahaman !

• Partial specialization:– Allows an entity not to belong to any

subclass– Example:

• Manager• Job type

– Use single line

Rules & Pemahaman !

Rules

• Deleting entity from a superclass deletes it also from the subclasses

• Inserting in a superclass, when attribute defined is filled must insert to the proper subclass as well

• Inserting in superclass of total specialization must insert into at least one subclassRules & Pemahaman !

Hierarchy & Lattice

• Hierarchy: a subclass only participates in one class/subclass relationship

• Example: Vehicle with Car and Trucks• Lattice: a subclass can participate in

more than one class/subclass relationship

• Example: an Engineering Manager, must be an Engineer, and also a Manager!

• The concept of multiple inheritance

Shared Sub-class

Alternative Diagrammatic NotationsSymbols for entity type / class, attribute and relationship

Displaying attributes

Displaying cardinality ratios

Various (min, max) notations

Notations for displaying specialization / generalization

Exercise

1. a property or description of an entity 2. a set of possible values for an attribute.3. an object in the real world that is distinguishable

from other objects such as the green dragon toy.4. an association among two or more entities.5. a collection of similar entities such as all of the toys

in the toy department.6. a collection of similar relationships7. a key constraint that indicates that one entity can be

associated with many of another entity. 8. an entity that cannot be identi.ed uniquely without

considering some primary key attributes of another identifying owner entity.

9. is the least number of instances of an entity that can participate in an instance of a relationship

1. Entity set

2. One-to-many relationship

3. Relationship set

4. Attribute

5. Weak entity

6. Many-to-many relationship

7. Domain

8. Instance

9. Relationship

Exercise1. a property or description of an entity 2. a set of possible values for an attribute.3. an object in the real world that is distinguishable

from other objects such as the green dragon toy.4. an association among two or more entities.5. a collection of similar entities such as all of the toys

in the toy department.6. a collection of similar relationships7. a key constraint that indicates that one entity can be

associated with many of another entity. 8. an entity that cannot be identi.ed uniquely without

considering some primary key attributes of another identifying owner entity.

9. is the least number of instances of an entity that can participate in an instance of a relationship

1. Domain

2. Instance

3. Relationship

4. Entity set

5. One-to-many relationship

6. Relationship set

7. Attribute

8. Weak entity

9. Many-to-many relationship

Exercise (cont.)

Exercise (cont.)• Develop ER-Diagram based on following facts !

– Manufacturers have a name, which we may assume is unique, an address, and a phone number

– Product have a model number and a type (e.g., television set). Each product is made by one manufacturer, and different manufacturers may have different products with the same model number. However, you may assume that no manufacturer would have two products with the same model number.

– Customers are identified by their unique social security number. They have email addresses, and physical addresses. Several customers may live at the same (physical) address, but we assume that no two customers have the same email address.

– An order has a unique order number, and a date. An order is placed by one customer. For each order, there are one or more products ordered, and there is a quantity for each product on the order.

More Complicated

?