DB slide - The Entity-Relationship Model Chapter 2...

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Unformatted text preview: The Entity-Relationship Model Chapter 2 Instructor: Vladimir Zadorozhny vladimir@sis.pitt.edu Information Science Program School of Information Sciences, 1 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny University of Pittsburgh Database: a Set of Relations (Tables) 2 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny Find the name of the customer with customer-id 192-83-7465 select customer.customer_name from customer where customer.customer_id = 192-83-7465 Database Design The process of designing the general structure of the database: Requires that we find a good collection of Requires that we find a good collection of relation schemas. Business decision What attributes should we record in the database? IS decision What relation schemas should we have and how should the attributes be distributed 3 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny among the various relation schemas? Deciding on the physical layout of the database Conceptual Database Design Conceptual design : ( ER Model is used at this stage.) What are the entities and relationships in the enterprise? What information about these entities and relationships should we store in the database? What are the integrity constraints or business rules that hold? 4 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny A database `schema in the ER Model can be represented pictorially ( ER diagrams ). Can map an ER diagram into a relational schema. ER Model Basics Entity: Real-world object distinguishable Employees ssn name lot Entity : Real world object distinguishable from other objects. An entity is described (in DB) using a set of attributes . Entity Set : A collection of similar entities. E.g., all employees. All entities in an entity set have the same set of 5 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny attributes. (Until we consider ISA hierarchies, anyway!) Each entity set has a key . Each attribute has a domain . ER Model Basics (Contd.) dname since name lot name Employees subor super- ssn Relationship : Association among two or more entities. E.g., Attishoo works in Pharmacy department. lot budget did Works_In Departments Employees ssn Reports_To subor- dinate super visor 6 Database Management Systems, R. Ramakrishnan and J. Gehrke INFSCI2710 Instructor: Vladimir Zadorozhny Relationship Set : Collection of similar relationships....
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This note was uploaded on 12/01/2011 for the course INFSCI 2710 taught by Professor Zadorozhnyy,v during the Winter '08 term at Pittsburgh.

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DB slide - The Entity-Relationship Model Chapter 2...

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