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Introduction to Database Systems Database Systems Lecture 5

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Textbook Recommended textbooks: ‘Database Systems: A practical approach to design, implementation and management’ by Connolly and Begg `A first course in database systems’ by Ullman and Widom.

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Why Study Databases? Databases are useful Many computing applications deal with large amounts of information Database systems give a set of tools for storing, searching and managing this information

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What is a Database? “A set of information held in a computer” Oxford English Dictionary “One or more large structured sets of persistent data, usually associated with software to update and query the data” Free On-Line Dictionary of Computing “A collection of data arranged for ease and speed of search and retrieval” Dictionary.com

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Databases Web indexes Library catalogues Medical records Bank accounts Stock control Personnel systems Product catalogues Telephone directories

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Database Systems A database system consists of Data (the database) Software Hardware Users We focus mainly on the software

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Database Users End users Use the database system to achieve some goal Application developers Write software to allow end users to interface with the database system

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Database Management Systems A database is a collection of information A database management system (DBMS) is the software than controls that information

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What the DBMS does Provides users with Data definition language (DDL) Data manipulation language (DML) Data control language (DCL) Often these are all the same language

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Data Dictionary - Metadata The dictionary or catalog stores information about the database itself This is data about data or ‘metadata’ Almost every aspect of the DBMS uses the dictionary

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File Based Systems File based systems Data is stored in files Each file has a specific format Programs that use these files depend on knowledge about that format

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Relational Systems Problems with early databases Navigating the records requires complex programs There is minimal data independence No theoretical foundations

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Relational Systems Information is stored as tuples or records in relations or tables There is a sound mathematical theory of relations Most modern DBMS are based on the relational model

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ANSI/SPARC Architecture ANSI - American National Standards Institute SPARC - Standards Planning and Requirements Committee 1975 - proposed a framework for DBs

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Internal Level Deals with physical storage of data Structure of records on disk - files, pages, blocks Indexes and ordering of records Used by database system programmers

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Conceptual Level Deals with the organisation of the data as a whole Abstractions are used to remove unnecessary details of the internal level Used by DBAs and application programmers

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External Level Provides a view of the database tailored to a user Parts of the data may be hidden Data is presented in a useful form Used by end users and application programmers

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Mappings Mappings translate information from one level to the next External/Conceptual Conceptual/Internal These mappings provide data independence

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ANSI/SPARC Architecture

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This Lecture in Exams Describe the three levels of the ANSI/SPARC model. You should include information about what each level is for, which users might be interested in which levels, and how the levels relate to one another. (2004/05, 7 marks)

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Next Lecture The Relational Model Relational data structure Relational data integrity Relational data manipulation For more information Connolly and Begg chapters 3 and 4 Ullman and Widom (2 ed.) Chapter 3.1, 5.1 E.F. Codd’s paper (there is a link on last year’s G51DBS webpage)