3902Ch3 - Data modeling using the entity-relationship model...

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Data modeling using the entity-relationship model Sept. 2009 Yangjun Chen ACS-3902 1 Outline: Data modeling using ER-model (Chapter 3 - 3rd, 4th, 5th ed.) Data modeling Entity-relationship model - Entity types - strong entities - weak entities - Relationships among entities - Attributes - attribute classification - Constraints - cardinality constraints - participation constraints ER-to-Relation-mapping
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Data modeling using the entity-relationship model Sept. 2009 Yangjun Chen ACS-3902 2 Entity-relationship model (ER model) P. 41-2: “ This model and its variations are frequently used for the conceptual design of database applications, and many database design tools employ its concepts .” ER model: is used to create a conceptual data model that reflects all the user data requirements. It includes detailed descriptions of entity types, relationships , and constraints no implementation details so can be used for communication with non-technical users
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Data modeling using the entity-relationship model Sept. 2009 Yangjun Chen ACS-3902 3 Example The company database keeps track of a company’s employees, departments, and projects: Requirements: concerning the department: 1. company is organized into departments 2. a department has a unique name, a unique number, and a specific employee is its’ manager 3. we track the start date for the manager function 4. a department may be in several locations 5. a department controls a number of projects concerning the project: 6. a project has a unique name, a unique number, and is in a single location
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Data modeling using the entity-relationship model Sept. 2009 Yangjun Chen ACS-3902 4 example continued concerning the employee: 7. each employee has a name, social insurance number, address, salary, sex, and birth date 8. an employee is assigned to one department but may work on several projects which are not necessarily controlled by the same department 9. we track the number of hours per week that an employee works on each project 10. we keep track of the direct supervisor of each employee 11. we track the dependents of each employee (for insurance purposes) concerning the dependent: 12. we record each dependent’s first name, sex, birth date, and relationship to the employee
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Data modeling using the entity-relationship model Sept. 2009 Yangjun Chen ACS-3902 5 The entities: employee department project dependent
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Data modeling using the entity-relationship model Sept. 2009 Yangjun Chen ACS-3902 6 The entities: bdate ssn name lname minit fname sex address salary birthdate name sex relationship name number location name number location employee department project dependent
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Data modeling using the entity-relationship model Sept. 2009 Yangjun Chen ACS-3902 7 With relationships: employee department project dependent works for manages works on dependents of controls supervision 1 N N 1 N M 1 N 1 1 N 1 supervisor supervisee partial constraint total constraint
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3902Ch3 - Data modeling using the entity-relationship model...

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