April 20022CS3X1 Database Design Introduction John Wordsworth Department of Computer Science The University of Reading Room 129, Ext 6544

April 20022CS3X2 Lecture objectives Understand how the course works and where to find the materials. Describe the history of the development of databases.

April 20022CS3X3 Textbook Connolly and Begg: Database Systems: A Practical Approach to Design Implementation and Management. Third edition, Addison Wesley, 2002, ISBN

April 20022CS3X4 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 20022CS3X5 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 20022CS3X6 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 20022CS3X7 More complex relationships students :: units flights :: airports (roles) course delivery :: room :: lecturer (3-ary) consultant :: patient :: illness :: treatment (4- ary)

April 20022CS3X8 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 20022CS3X9 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 20022CS3X10 Emphasis In hierarchical and network systems –record navigation In relational systems –specification of mathematical processes on bulk data –(compare the matrix in mathematics)

April 20022CS3X11 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 20022CS3X12 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.