lecture-09-er-diagrams

lecture-09-er-diagrams - The Entity-Relationship Model T....

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Unformatted text preview: The Entity-Relationship Model T. M. Murali September 22, 2010 T. M. Murali September 22, 2010 CS 4604: E/R model Till the Midterm Examination I Relational Data Models I The Entity-Relationship (ER) model I The relational model I Converting E/R diagram to relational designs. I At this point, you will know how to 1. Identify all entities and relationships and describe them using an E/R diagram . 2. Convert the E/R model to a number of relations in a relational schema. I Use all these ideas to design your own database application in your project. T. M. Murali September 22, 2010 CS 4604: E/R model Why Learn About Database Modelling? I The way in which data is stored is very important for subsequent access and manipulation by SQL. I Properties of a good data model: I It is easy to write correct and easy to understand queries. I Minor changes in the problem domain do not change the schema. I Major changes in the problem domain can be handled without too much difficulty. I Can support efficient database access. T. M. Murali September 22, 2010 CS 4604: E/R model Purpose of the E/R Model I The Entity-Relationship (E/R) model enables us to draw diagrams of database designs I Represent different types of data and how they relate to each other. I The design is a drawing called the E/R diagram . I When designing E/R diagrams, forget about relations/tables ; only consider how to model the information you need to represent in your database. I In two weeks, we will learn how to convert an E/R diagram to a relational schema. E/R design Relational schema Relational DBMS Ideas T. M. Murali September 22, 2010 CS 4604: E/R model Entity Sets I An entity is an (abstract) object of some sort. I An entity set is a collection of similar entities. I Entities have attributes I An attribute is a property of the entities in an entity set I In this class, our convention is to useatomicattributes (strings, numbers, . . . ) T. M. Murali September 22, 2010 CS 4604: E/R model Entity Sets...
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This note was uploaded on 12/24/2011 for the course CS 4604 taught by Professor Cmmalik during the Fall '08 term at Virginia Tech.

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lecture-09-er-diagrams - The Entity-Relationship Model T....

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