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chapter2 part2 - The Evolution of Data Models Chapter 2...

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37 Chapter 2 Data Models part 2 BUS 173 Winter 2011 Dr. Hamouda 38 Types of Models Hierarchical Network Relational The Evolution of Data Models 39 The Relational Model Developed by E.F. Codd (IBM) in 1970 Foundation is mathematical concept: relation (Table) Matrix consisting of row/column intersections Each row in a relation is called a tuple Each column represents an attribute Table manipulations are based on mathematical concepts (Union, intersection,…) 40 The Relational Model Relational models were considered impractical in 1970 Model was conceptually simple at expense of computer overhead Performs same functions provided by hierarchical & network data model Hides complexity from the user User sees the relational database as a collection of tables that store the data 41 Tables are related to each other by sharing a common value in a column (attribute) The Relational Model (cont’d.) 42 The Relational Model (cont’d.) Relational diagram is a representation of entities, attributes within the entity and relationships between those entities Relationship type (1:1, 1:M. M:N)
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4343 Example of a customer data file File System (Chapter 1) 44 The Relational Model (cont’d.) Relational models were dominant due to the powerful and flexible query language (SQL) SQL-based relational database application involves three parts: User interface Allows end user to interact with the data Set of tables stored in the database Tables are independent
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