Entity-Relation Modeling
Hun Myoung Park, Ph.D.,
Public Management and Policy Analysis ProgramGraduate School of International Relations
International University of Japan
OutlineBusiness RulesEntity-Relation ModelEntity of E-R ModelAttribute of E-R ModelRelationship of E-R ModelDegree of RelationshipCardinality of a RelationshipCASE 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.”
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Entity-Relationship ModelA 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 1976Represented by entity-relationship diagram
(ERD)
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Entity-Relationship DiagramE-R diagram (ERD) represents the abstract
and conceptual relationships in ERM. Components of ERDEntity with attributesRelationship among entitiesCardinality
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Entity of E-R Model 1Represented by a rectangle or box in ERDName in uppercase Name as singular noun formIncludes a set of attributesEntity type versus entity instance
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Entity of E-R Model 2Entity 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 3Associative entityAssociate the instances of entity typesContains 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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Attribute of E-R Model 1A property of an entity typeSingular none or none phraseSentence-casedRequired (must have values) in boldface
v.s. optional attribute (may not)
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Attribute of E-R Model 2Simple (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 […]
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Relationship of E-R Model 1Connectivity (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
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Relationship of E-R Model 2Represented by a diamond in the original
Chen notation and by a connecting lineConnectivity label (name) is a verb phrase
in sentence-caseEither an active or passive form (e.g.,
manages or managed by)
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Degree of a Relationship 1The 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
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Degree of a Relationship 2Binary 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.
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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.
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Cardinality (Constraint) 2Minimum 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”
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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; mandatorySymbols are used instead of numbers in
ERD
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NormalizationNormalization simplifies a database to
make it compliant with the concept of the normal form.
Eliminate duplicate and/or abnormal records
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CASE ToolsCASE tools are very useful in system design
and development stage, facilitating communications among stakeholders.
Professional CASE tools, CaseStudio, Microsoft Visio (Professional Edition)
MySql Workbenchhttp://dev.mysql.com/downloads/
workbench/
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An Example of CASE ToolsCASE Studio II and MySql WorkbenchGUI Provides flexible ways to modify.Define the database structure that matches
with the E-R diagramGenerate SQL commands to create
corresponding tables based on E-R diagram designed.
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E-R Diagram (CaseStudio 2)
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