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Entity-Relation Modeling Hun Myoung Park, Ph.D., Public Management and Policy Analysis Program Graduate School of International Relations International University of Japan
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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 2
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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.” 3
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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) 4
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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 5
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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 6
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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 7
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Entity of E-R Model 3 Associative entity 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 8
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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) 9
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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 […] 10
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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 11
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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) 12
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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 13
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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. 14
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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. 16
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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 ” 17
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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; mandatory Symbols are used instead of numbers in ERD 18
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Normalization Normalization simplifies a database to make it compliant with the concept of the normal form. Eliminate duplicate and/or abnormal records 22
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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, Microsoft Visio (Professional Edition) MySql Workbench http://dev.mysql.com/downloads/workbenc h/ 23
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An Example of CASE Tools CASE Studio II and 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. 24
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E-R Diagram (CaseStudio 2)
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