1. Entity-Relation Modeling
Hun Myoung Park, Ph.D.,
Public Management and Policy Analysis Program
Graduate School of International Relations
International University of Japan

2. Outline Business Rules Entity-Relation Model Entity of E-R Model
Attribute of E-R Model
Relationship of E-R Model
Degree of Relationship
Cardinality of a Relationship
CASE Tools

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Business Rules
“A statement that defines or constrains some aspect of the business”
“Govern how data are handled and stored”
“Derived from policies, procedures, events, functions, and other business objects”
“Documenting rules and policies of an organization that govern data is exactly what data modeling is all about.”

5. Entity-Relationship Model5
Entity-Relationship Model
A database modeling method that produces “a detailed, logical representation of the data”
Produces a conceptual schema in a relational database
Introduced by Peter Chen in 1976
Represented by entity-relationship diagram (ERD)

6. Entity-Relationship Diagram6
Entity-Relationship Diagram
E-R diagram (ERD) represents the abstract and conceptual relationships in ERM.
Components of ERD
Entity with attributes
Relationship among entities
Cardinality

7. Entity of E-R Model 1 Represented by a rectangle or box in ERD7
Entity of E-R Model 1
Represented by a rectangle or box in ERD
Name in uppercase
Name as singular noun form
Includes a set of attributes
Entity type versus entity instance

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Entity of E-R Model 2
Entity type is “a collection of entities that share common properties”
Entity instance is “a single occurrence of an entity type”
Strong (unique/independent) entity type versus weak (dependent) entity type

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Entity of E-R Model 3
Associative entity, bridge/intermediary/intersection/junction/link ing/mapping table, many-to-many solver
Associate the instances of entity types
Contains attributes that are peculiar to the relationship among the entity instances.
Relationship in a rectangular with rounded corners or dashed line

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Strong Relationship 1
A strong (identifying) relationship exists “when the primary key of the related entity contains a primary key component of the parent entity” (p.331) It is represented by a solid line. The relationship between COURSE and CLASS tables below is strong because, Crs_code in CLASS (child entity in the 1:M relationship) inherits a primary key component from COURSE (parent entity).

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Strong Relationship 2

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Weak Relationship 1
A weak (non-identifying) relationship exists “if the primary key of the related entity does not contain a primary key component of the parent entity” (p.330). It is represented by a dashed line. In the following example, Crs_code in CLASS (child entity) is not a part of primary key and does not inherit a primary key component from COURSE (parent entity). Note that Crs_code in CLASS is a foreign key.

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Weak Relationship 2

14. Attribute of E-R Model 1 A property of an entity type14
Attribute of E-R Model 1
A property of an entity type
Singular none or none phrase
Sentence-cased
Required (must have values) in boldface v.s. optional attribute (may not)

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Attribute of E-R Model 2
Simple (atomic) attribute v. s. composite attribute (having meaningful components parts such as last name and first name) in (…)
Single-valued v.s. multi-valued attribute in {…}
Stored v.s. derived attribute (e.g., age calculated from date of birth) in […]

16. Relationship of E-R Model 116
Relationship of E-R Model 1
Connectivity (association) representing an interaction among instances of entity types
Relationship type is “a meaningful association among entity types”
Relationship instance is “an association among entity instances

17. Relationship of E-R Model 217
Relationship of E-R Model 2
Represented by a diamond in the original Chen notation and by a connecting line
Connectivity label (name) is a verb phrase in sentence-case
Either an active or passive form (e.g., manages or managed by)

18. Degree of a Relationship 118
Degree of a Relationship 1
The number of entity types that participate in a relationship.
Unary (recursive) relationship is a relationship between the instances of one entity type
Examples are marriage and supervision in an organization

19. Degree of a Relationship 219
Degree of a Relationship 2
Binary relationship is a relationship between instances of two entity types.
Binary relationship is most common
Ternary relationship is a simultaneous relationship among instances of three entity types.

21. Cardinality (Constraint) 121
Cardinality (Constraint) 1
“The number of instances of entity B that can (or must) be associated with each instance of entity A”
Cardinality of a relationship expresses the minimum and maximum number of entity occurrences associated with one occurrence of the related entity.

22. Cardinality (Constraint) 222
Cardinality (Constraint) 2
Minimum cardinality: minimum number of instances of entity B that may be associated with each instance of entity A
Maximum cardinality: maximum number of instances of entity B that may be associated with each instance of entity A
Zero (0) cardinality implies “optional,” cardinality one (1) means “mandatory”

23. Cardinality (Constraint) 323
Cardinality (Constraint) 3
(0,1) zero minimum or one maximum; optional
(1,1) one and only one; mandatory
(0, N) one or many; optional
(1,N) one or many; mandatory
Symbols are used instead of numbers in ERD

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CASE Tools
CASE tools are very useful in system design and development stage, facilitating communications among stakeholders.
Professional CASE tools, CaseStudio II, Microsoft Visio (Professional Edition)
MySql Workbench h/

28. An Example of CASE Tools28
An Example of CASE Tools
MySql Workbench
GUI Provides flexible ways to modify.
Define the database structure that matches with the E-R diagram
Generate SQL commands to create corresponding tables based on E-R diagram designed.

29. E-R Diagram (CaseStudio 2)

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32. References
Hoffer, Jeffrey A., V. Ramesh, and Heikki Topi Modern database management, 10th ed. Pearson Education.