Database Systems: Learning Outcomes. Examples of Database Application. Introduction

Transcription

1 Chapter 1 Part One: Introduction to 1 Systems: Thomas Connolly, Carolyn Begg, System, A Practical Approach to Design Implementation and Management, 4 th Edition, Addison Wesley Introduction Traditional File-based Systems Approach Roles in the Environment Advantages & Disadvantages of DBMS Learning Outcomes 1-1 Chapter 1 Part One: Introduction to 2 Introduction Examples of Application DBMS System Apps. Purchases from the supermarket Purchases using credit card Booking a holiday at the travel Using the local library Taking out insurance Using the Internet Studying at university Chapter 1 Part One: Introduction to 3 Chapter 1 Part One: Introduction to 4

2 Chapter 1 Part One: Introduction to 5 File-based Approach File-based Processing Traditional file-based system An early file-based system (tradditionl way) use the manual filing system A mistake database system We can learn from that mistake Prefevent from reapeating the problem that coused by this mistake Understanding how the file system works Collection of application program that perform services for the end users (e.g reports) Program defines and manages it s own data Chapter 1 Part One: Introduction to 6 File-based Processing Limitations of File-based Separation and isolation When data is isolated in separate files, it is more difficult to access data that should be available. Duplication Uncontrolled duplication of data accour Program and data dependence Because the physical structure and storage of the data files and records are defined in the application code (program), so the changes to an existing structure are difficult to make. Chapter 1 Part One: Introduction to 7 Chapter 1 Part One: Introduction to 8

3 Chapter 1 Part One: Introduction to 9 Limitations of File-based Incompatible file format Because the structure of files is embedded in the application programs, the structures are dependent on the application programming language. Fixed queries and proliferation of application programs The requirement for new or modified queries grew Limitation of file-based factors: (1) the definition of the data is embedded in the application programs, rather than being stored separately and independently; (2) there is no control over the access and manipulation of data beyond that imposed by the application programs. Chapter 1 Part One: Introduction to 10 Definition A shared collection of logically related data, and a description of this data, designed to meet the information needs of an organization. Logical Related When we analyze the information needs of an organization, we attempt to identify entities, attributes, and relationships. Entities: is a distinct object (a person, place, thing, concept, or event) in the organization that is to be represented in the database Attributes: is a property that describes some aspect of the object that we wish to record. Relationship: is an association between entities. characteristics A large repository of data that can be used simultaneously by many departments and users. All data items are integrated with a minimum amount of duplication. Shared resource. Holds not only the organization s operational data but also a description of this data (a self-describing and integrated data files) System catalog Metadata Data dictionary Overhead data Chapter 1 Part One: Introduction to 11 Chapter 1 Part One: Introduction to 12

4 Chapter 1 Part One: Introduction to 13 Management System (DBMS) Program-data independencies The nature of database Data abstraction One advantage of this approach, is that we can change the internal definition of an object without affecting the users of the object, provided the external definition remains the same. Chapter 1 Part One: Introduction to 14 Management System (DBMS) A software system that enables users to define, create, maintain, and control access to the database. Facilities: Data definition language (DDL) - allows users to specify the data types and structures and the constraints on the data to be stored in the database. Data manipulation language (DML)/query language - allows users to insert, update, delete, and retrieve data from the database. Structured query language (SQL) standard language for DBMS. Security system - which prevents unauthorized users accessing the database. Integrity system - which maintains the consistency of stored data. Concurrency control system - which allows shared access of the database. Approach as DBMS Recovery control system - which restores the database to a previous consistent state following a hardware or software failure. User-accessible catalog - which contains descriptions of the data in the database. Chapter 1 Part One: Introduction to 15 Chapter 1 Part One: Introduction to 16

5 Chapter 1 Part One: Introduction to 17 DBMS Environment DBMS Environment Hardware Client-server architecture Software dbms, os, network, application Data Schema, subschema, table, attribute People Data administrator & database administrator designer: logical & physical Application programmer End-user: naive & sophisticated Procedure Start, stop, log on, log off, back up, recovery Chapter 1 Part One: Introduction to 18 Roles in the Environment Advantages of DBMS Data Administrator (DA) Management of data resources Ensure database development support corporate objectives Administrator (DBA) Physical realization of database More technically oriented Designers Logical Identifying data Physical Realization of logical database Application Programmers Implement application program for user End Users (Naïve and Sophisticated) Control redundancy Consistency Integrity Security Concurrency control Backup & recovery Data standard More information Data sharing & conflict control Productivity & accessibility Economy of scale Maintenance Chapter 1 Part One: Introduction to 19 Chapter 1 Part One: Introduction to 20

6 Chapter 1 Part One: Introduction to 21 Complexity Size Cost Software Hardware Conversion Performance Vulnerability Limitations of DBMS Systems: Thomas Connolly, Carolyn Begg, System, A Practical Approach to Design Implementation and Management, 4 th Edition, Addison Wesley 1-22 Chapter 1 Part One: Introduction to 22