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Database Design Introduction John Wordsworth Department of Computer Science The University of Reading [email protected] Room 129, Ext 6544 April 2002 2CS3X 1 Lecture objectives Understand how the course works and where to find the materials. Describe the history of the development of databases. April 2002 2CS3X 2 Textbook Connolly and Begg: Database Systems: A Practical Approach to Design Implementation and Management. Third edition, Addison Wesley, 2002, ISBN 0-201-34287-1 April 2002 2CS3X 3 Data processing Many applications. Each application entirely separately. Each design of data was closely coupled to the design of the program. Hard to exchange data between applications. Every new application had to design its own data files from scratch. April 2002 2CS3X 4 Example • The marketing division has a customer file – people it sends catalogues to • The sales division also has a customer file – people it sends invoices to • Sales sends invoice; customer has moved; new address to sales; marketing continue to send catalogues to old address. April 2002 2CS3X 5 Data • Information about people and things – person (name, address, age, job-title, annual salary) – engine (cyls, capacity, fuel, turbo, output) • Relationships between things – department :: teaching-staff – hall :: students April 2002 2CS3X 6 More complex relationships • • • • students :: units flights :: airports (roles) course delivery :: room :: lecturer (3-ary) consultant :: patient :: illness :: treatment (4ary) April 2002 2CS3X 7 What is a database? • General purpose data repository • Based on particular data model • Managed by a DBMS that provides: – Data Definition Language – Data Manipulation language April 2002 2CS3X 8 Three models of data • Hierarchical – designed for 1:M relationships; more complex relationships possible but very artificial • Network – based on sets defined by logical links • Relational – based on tables – initially believed too costly; now dominant April 2002 2CS3X 9 Emphasis • In hierarchical and network systems – record navigation • In relational systems – specification of mathematical processes on bulk data – (compare the matrix in mathematics) April 2002 2CS3X 10 The ANSI-SPARC three-layer architecture • External schema – the views of the various users of the data • Conceptual schema – a consolidation and rationalisation of the external schemas • Internal schema – a mapping of the conceptual schema on to the physcial data management facilities April 2002 2CS3X 11 Key points Data processing was originally file-based. Data is information about things and their relationships. Modern databases are general-purpose data stores. There are three data models supported by DBMSs. There has been a shift of emphasis, making data independent of applications. The ANSI-SPARC model sets a standard for database design. April 2002 2CS3X 12