Introduction To Databases PDF

Chapter 1 Introduction to Databases Transparencies © Pearson Education Limited 1995, 2005 Chapter 1 - Objectives  Some common uses of database systems.  Characteristics of file-based systems.  Problems with file-based approach.  Meaning of t...

Chapter 1 Introduction to Databases Transparencies © Pearson Education Limited 1995, 2005 Chapter 1 - Objectives  Some common uses of database systems.  Characteristics of file-based systems.  Problems with file-based approach.  Meaning of the term database.  Meaning of the term Database Management System (DBMS). © Pearson Education Limited 1995, 2005 Chapter 1 - Objectives  Typical functions of a DBMS.  Major components of the DBMS environment.  Personnel involved in the DBMS environment.  History of the development of DBMSs.  Advantages and disadvantages of DBMSs. © Pearson Education Limited 1995, 2005 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 © Pearson Education Limited 1995, 2005 File-Based Systems  Collection of application programs that perform services for the end users (e.g. reports).  Each program defines and manages its own data. © Pearson Education Limited 1995, 2005 File-Based Processing © Pearson Education Limited 1995, 2005 Limitations of File-Based Approach  Separation and isolation of data – Each program maintains its own set of data. – Users of one program may be unaware of potentially useful data held by other programs.  Duplication of data – Same data is held by different programs. – Wasted space and potentially different values and/or different formats for the same item. © Pearson Education Limited 1995, 2005 Limitations of File-Based Approach  Data dependence – File structure is defined in the program code.  Incompatible file formats – Programs are written in different languages, and so cannot easily access each other’s files.  Fixed Queries/Proliferation of application programs – Programs are written to satisfy particular functions. – Any new requirement needs a new program. © Pearson Education Limited 1995, 2005 Database Approach  Arose because: – Definition of data was embedded in application programs, rather than being stored separately and independently. – No control over access and manipulation of data beyond that imposed by application programs.  Result: – the database and Database Management System (DBMS). © Pearson Education Limited 1995, 2005 Database  Shared collection of logically related data (and a description of this data), designed to meet the information needs of an organization.  System catalog (metadata) provides description of data to enable program–data independence.  Logically related data comprises entities, attributes, and relationships of an organization’s information. © Pearson Education Limited 1995, 2005 Database Management System (DBMS)  A software system that enables users to define, create, maintain, and control access to the database.  (Database) application program: a computer program that interacts with database by issuing an appropriate request (SQL statement) to the DBMS. © Pearson Education Limited 1995, 2005 Database Management System (DBMS) © Pearson Education Limited 1995, 2005 Database Approach  Data definition language (DDL). – Permits specification of data types, structures and any data constraints. – All specifications are stored in the database.  Data manipulation language (DML). – General enquiry facility (query language) of the data. © Pearson Education Limited 1995, 2005 Database Approach  Controlled access to database may include: – a security system – an integrity system – a concurrency control system – a recovery control system – a user-accessible catalog. © Pearson Education Limited 1995, 2005 Views  Allows each user to have his or her own view of the database.  A view is essentially some subset of the database. © Pearson Education Limited 1995, 2005 Views - Benefits  Reduce complexity  Provide a level of security  Provide a mechanism to customize the appearance of the database  Present a consistent, unchanging picture of the structure of the database, even if the underlying database is changed © Pearson Education Limited 1995, 2005 Components of DBMS Environment © Pearson Education Limited 1995, 2005 Components of DBMS Environment  Hardware – Can range from a PC to a network of computers.  Software – DBMS, operating system, network software (if necessary) and also the application programs.  Data – Used by the organization and a description of this data called the schema. © Pearson Education Limited 1995, 2005 Components of DBMS Environment  Procedures – Instructions and rules that should be applied to the design and use of the database and DBMS.  People © Pearson Education Limited 1995, 2005 Roles in the Database Environment  Data Administrator (DA)  Database Administrator (DBA)  Database Designers (Logical and Physical)  Application Programmers  End Users (naive and sophisticated) © Pearson Education Limited 1995, 2005 History of Database Systems  First-generation – Hierarchical and Network  Second generation – Relational  Third generation – Object-Relational – Object-Oriented © Pearson Education Limited 1995, 2005 Advantages of DBMSs  Control of data redundancy  Data consistency  More information from the same amount of data  Sharing of data  Improved data integrity  Improved security  Enforcement of standards  Economy of scale © Pearson Education Limited 1995, 2005 Advantages of DBMSs  Balance conflicting requirements  Improved data accessibility and responsiveness  Increased productivity  Improved maintenance through data independence  Increased concurrency  Improved backup and recovery services © Pearson Education Limited 1995, 2005 Disadvantages of DBMSs  Complexity  Size  Cost of DBMS  Additional hardware costs  Cost of conversion  Performance  Higher impact of a failure © Pearson Education Limited 1995, 2005