Data Modeling Part 2 - Data Modeling, Part 2 More on...

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More on Relationships: Cardinality and Modality Data Modeling, Part 2 When Arrow appears, left click anywhere or press Page Down to
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Components of an ERD (Review) Business Rules Information from the user’s business environment that governs how his data is used—for example, policies, procedures , constraints, regulations, formulas and calculations . Entity An object in the user’s business environment that he wants to track or keep up with –for example, customers, orders, employees, products, services . Attribute A data item that describes an entity—for example, employee ID, last name, date of hire, number in inventory . An IDENTIFIER --one or more attributes that uniquely identify one member of the entity. For example, Product_Number, Employee_ID, Order_Number. Identifiers are also called Primary Keys Relationship An association between entities—for example, customer places an order, player plays on a team. ..
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Types of Relationships. .. Unary (Recursive) –one entity in relationship (entity associated with itself) Binary—two entities in relationship (entity associated with another entity) Ternary—three entities in relationship (entity associated with two other entities in same relationship) Number of entity types that participate in a relationship Largest number of relationships are binary Sometimes Type is referred to as Degree
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Binary Relationships Student enrolls in section of a course Customer places an order Book has author One relationship with two entities…
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Unary(Recursive) Relationship. . Team plays a team Employee manages an Employee One relationship with one entity Commonly called “Recursive” instead of unary…
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Ternary Relationship Engineer uses Equipment on a Project One relationship with three entities…
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More on Relationships ... In our first ERD’s, we used a line to indicate a relationship
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This note was uploaded on 09/21/2011 for the course CGS 2545C CGS 2545c taught by Professor L during the Summer '10 term at University of Central Florida.

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Data Modeling Part 2 - Data Modeling, Part 2 More on...

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