454.3-09.Introduction

454.3-09.Introduction - Database Systems II Introduction...

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CMPT 454, Simon Fraser University, Fall 2009, Martin Ester 1 Database Systems II Introduction CMPT 454, Simon Fraser University, Fall 2009, Martin Ester 2 Database Systems I Recap A Database Management System (DBMS) is a software package designed to store, manage and retrieve databases. A Database System (DBS) consists of two components: the DBMS the database.
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CMPT 454, Simon Fraser University, Fall 2009, Martin Ester 3 Database Systems I Recap Why use a DBS? - Logical data independence. - Physical data independence. - Efficient access. - Reduced application development time. - Data integrity and security. - Concurrent access / concurrency control. - Recovery from crashes. CMPT 454, Simon Fraser University, Fall 2009, Martin Ester 4 Database Systems I Recap A data model is a collection of concepts for describing data (a formal language !). A schema is a description of a particular collection of data (database), using the given data model. The relational data model is the most widely used model today. Main concept: relation , basically a table with rows and columns. Every relation has a schema , which describes the columns, or fields.
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5 Database Systems I Recap The conceptual schema defines the logical structure of the whole database. An external schema ( view ) describes how some user sees the data (restricted access, derived data). The physical schema describes the storage and index structures of the database. Physical Schema Conceptual Schema View 1 View 2 View 3 CMPT 454, Simon Fraser University, Fall 2009, Martin Ester 6 Database Systems I Recap Relational database : a set of relations Relation: made up of 2 parts: Instance : a table , with rows and columns. #Rows = cardinality , #attributes = degree / arity. Schema : specifies name of relation, plus name and type of each attribute. e.g. Students( sid : string, name : string, login : string, age : integer, gpa : real). Can think of a relation as a
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This note was uploaded on 10/07/2009 for the course CS 12042 taught by Professor Martinester during the Fall '09 term at Simon Fraser.

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454.3-09.Introduction - Database Systems II Introduction...

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