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Introduction to Electronic Government Entity-Relationship Model Tuesday, October 21, 2014

Introduction to Electronic Government Entity-Relationship Model Tuesday, October 21, 2014. Hun Myoung Park, Ph.D. Public Management & Policy Analysis Program Graduate School of International Relations. Layout. E-R Modeling Components of E-R Model Degree of a Relationship

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Introduction to Electronic Government Entity-Relationship Model Tuesday, October 21, 2014

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  1. Introduction to Electronic GovernmentEntity-Relationship ModelTuesday, October 21, 2014 Hun Myoung Park, Ph.D. Public Management & Policy Analysis ProgramGraduate School of International Relations

  2. Layout • E-R Modeling • Components of E-R Model • Degree of a Relationship • Cardinality of a Relationship • CASE Tools

  3. 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.”

  4. 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)

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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)

  10. 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 […]

  11. 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

  12. 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)

  13. 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

  14. 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.

  15. 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. 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. 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. Normalization • Normalization simplifies a database to make it compliant with the concept of the normal form. • Eliminate duplicate and/or abnormal records

  19. 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/workbench/

  20. 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.

  21. E-R Diagram (CaseStudio 2)

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