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6 - 
 Announcements •  Overview –  –  – ...

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1/16/10 1 Announcements Overview: 1. Introduction 2. Conceptual DB design: ER Models 3. Relational Algebra 4. SQL Monday: MLK day Early warning Wed 1/27 (swap of class disc. sect.) Class will be from 8-8:50am in 234 Wellman Discussion Section will be at 3:10-4pm in 234 Wellman Homework 2 (RA, simple SQL): Out next week; due: one week after ECS‐165A WQ'10 1 Modeling Alternatives: Attribute | Entity | Relationship Should office be an attribute of Employee ? Should office be a separate Entity Type ? Most attributes can be “promoted” to an Entity Set … and some Entities can be “demoted” to an attribute value This is one reason why there are so many different ways to design a schema ECS‐165A WQ'10 2 Project Employee Assignment num name due ssn name office
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1/16/10 2 Modeling Alternatives: Attribute | Entity | Relationship What are some reasons to model Office as an Entity Set? An employee can have more than one office Alternative? There are additional attributes of Office Office needs to participate in other relationships E.g., a relationship set connecting to furniture or telephones or network drops (located in the office) ECS‐165A WQ'10 3 Project Employee Assignment num name due ssn name Office Assigned Office num Modeling Alternatives: Attribute | Entity | Relationship Example when Office should be an entity set Office needs to participate in other relationship sets ECS‐165A WQ'10 4 Project Employee Assignment num name due ssn name Office Assigned Office num size Located In Furniture type id
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1/16/10 3 Modeling Alternatives: Attribute | Entity | Relationship Example: SUPPLIER offers PRODUCTS at PRICE Where does PRICE go? ECS‐165A WQ'10 5 Key Constraints as Described in the Textbook Limiting participation in a relationship set to at most 1 entity Same as maximum cardinality of 1 ( 0.. 1 in our notation)
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