Database Systems PDF

Chapter 3: Database Systems © 2015 Pearson Education Limited 2015 Examples of Database Applications  Purchases from the supermarket  Purchases using your credit card  Booking a holiday at the travel agents  Using the local library  Taking out insurance  Renting a video...

Chapter 3: Database Systems © 2015 Pearson Education Limited 2015 Examples of Database Applications  Purchases from the supermarket  Purchases using your credit card  Booking a holiday at the travel agents  Using the local library  Taking out insurance  Renting a video  Using the Internet  Studying at university Chapter 1 Definitions  Data: stored representations of meaningful objects and events or  Referred to facts concerning objects and events that could be recorded and stored on computer media  Structured: numbers, text, dates  Unstructured: images, video, documents  Information: data processed to increase knowledge in the person using the data  Metadata: data that describes the properties and context of user data Chapter 1 3 Definitions of Database  Def 1: Database is an organized collection of logically related data  Def 2: A database is a shared collection of logically related data that is stored to meet the requirements of different users of an organization  Def 3: A database is a self-describing collection of integrated records  Def 4: A database models a particular real world system in the computer in the form of data Chapter 1  What is a Database  Shared collection of logically related data (and a description of this data), designed to meet the information needs of an organization.  Databases are a method for storing data in a structured way on a computer, to make it easier to store, search, and work with that data.  Data is typically stored in tables in a database. You can visualize each table as having columns, or fields, which hold particular categories of data (e.g. first name), and rows, or records, which hold all of the information about a particular thing (e.g. a customer). Chapter 1 5  Figure 1-1a Data in Context Context helps users understand data Chapter 1  Graphical displays turn data into useful information that managers can use for decision making and interpretation Chapter 1  Descriptions of the properties or characteristics of the data, including data types, field sizes, allowable values, and data context Chapter 1  Before Databases: File Processing System  Commercial applications introduced File Processing System  A File Processing System, in computer science, is a method to read, write, modify, and store data in files  A collection of application programs that perform services for the end-users such as production of reports  Each program defines and manages its own data Chapter 1 9 File Processing Systems Library Examination Registration Library Examination Registration Applications Applications Applications Library Examination Registration Data Data Data Files Files Files Chapter 1 Program and Data Interdependence 10  File Processing Systems Library Examination Registration Reg_Number Reg_Number Reg_Number Name Name Name Father Name Address Father Name Books Issued Class Phone Fine Semester Address Grade Class Chapter 1 11 Disadvantages of File Processing  Program-Data Dependence  File structure is defined in the program code.  All programs maintain metadata for each file they use  Duplication of Data (Data Redundancy)  Different systems/programs have separate copies of the same data  Same data is held by different programs.  Wasted space and potentially different values and/or different formats for the same item.  Limited Data Sharing  No centralized control of data  Programs are written in different languages, and so cannot easily access each other’s files. Chapter 1 Disadvantages of File Processing  Lengthy Development Times  Programmers must design their own file formats  Excessive Program Maintenance  80% of information systems budget  Vulnerable to Inconsistency  Change in one table need changes in corresponding tables as well otherwise data will be inconsistent Chapter 1 13  Problems with Data Dependency  Each application programmer must maintain their own data  Each application program needs to include code for the metadata of each file  Each application program must have its own processing routines for reading, inserting, updating and deleting data  Lack of coordination and central control  Non-standard file formats Chapter 1 Problems with Data Redundancy  Waste of space to have duplicate data  Causes more maintenance headaches  The biggest problem:  When data changes in one file, could cause inconsistencies (Vulnerable to Inconsistency)  Compromises data integrity (data reliability) Chapter 1 SOLUTION: The DATABASE Approach  Central repository of shared data  Data is managed by a controlling agent  Stored in a standardized, convenient form This requires a Database and Database Management System (DBMS) Chapter 1  Advantages of Database Approach Library Examination Registration Library Examination Registration Applications Applications Applications Database Management System - Data Sharing - Data Independence - Controlled Redundancy University - Better Data Integrity Students Database Chapter 1 17 Database Management System  A software system that is used to create, maintain, and provide controlled access to users of a database  (Database) application program: A computer program that interacts with database by issuing an appropriate request (SQL statement) to the DBMS Chapter 1 Database Management System DBMS manages data resources like an operating system manages hardware resources Chapter 1 Chapter 1 Chapter 1  Database Models Database model: A conceptual view of a database  Relational database model  Object-oriented database model Chapter 1 9-22 The Entity Relational Model ER is a model for identifying entities to be represented in the database and representation of how those entities are related. The ER data model specifies enterprise schema that represents the overall logical structure of a database graphically. Chapter 1 23 Chapter 1 24 Chapter 1 25 Chapter 1 26 Chapter 1 27 Chapter 1 28 Chapter 1 29 Chapter 1 30 Chapter 1 31 Chapter 1 32 End of Slides Chapter 1 33