Data vs. Information
• Data:– Unprocessed information• Information:– Data processed to reveal meaning– Accurate, relevant, and timely information is key to good decision making– Good decision making is key to survival in global environment
Introducing the Database and the DBMS
• Database — shared, integrated computer structure that houses:• End user data (raw facts)• Metadata (data about data)• DBMS (database management system):• Collection of programs that manages database structure and controls access to data• Possible to share data among multiple applications or users• Makes data management more efficient and effective
DBMS Makes Data Management More Efficient and Effective
• End users have better access to more and better-managed data• Promotes integrated view of organization’s operations• Probability of data inconsistency is greatly reduced• Possible to produce quick answers to ad hoc queries
Types of Databases
• Single-user:– Supports only one user at a time• Multi-user:– Supports multiple users at the same time• Workgroup:– Multi-user database that supports a small group of users or a single department• Enterprise:– Multi-user database that supports a large group of users or an entire organization
Location of Databases
• Centralized:– Supports data located at a single site• Distributed:– Supports data distributed across several sites
Why Database Design is Important
• Defines the database’s expected use• Avoid redundant data (unnecessarily duplicated)• Poorly designed database generates errors -> leads to bad decisions -> can lead to failure of organization
The Historical Roots of Database: Files and File Systems
• Although managing data through file systems is largely obsolete– Understanding relatively simple characteristics of file systems makes complexity of database design easier to understand– Knowledge of file systems is helpful if you plan to convert an obsolete file system to a DBMS
Conversion from Manual File System to Computer File System
• Could be technically complex, requiring hiring of Data Processing (DP) specialists to create file structures, writes software and design application programs.• Initially, computer files were similar in design to manual files (see Figure 1.3)
Contents of Customer File
Contents of the Agent File
Problems with File System Data Management
• Every task requires extensive programming in a third-generation language (3GL)– Programmer must specify task and how it must be done• Modern databases use fourth-generation language (4GL)– Allows user to specify what must be done without specifying how it is to be done
Programming in 3GL
• Time-consuming, high-level activity• Programmer must be familiar with physical file structure• As system becomes complex, access paths become difficult to manage and tend to produce malfunctions• Complex coding establishes precise location of files and system components and data characteristics• Ad hoc queries are impossible• Writing programs to design new reports is time consuming• As number of files increases, system administration becomes difficult• Making changes in existing file structure is difficult• File structure changes require modifications in all programs that use data in that file
• Modifications are likely to produce errors, requiring additional time to “debug” the program• Security features hard to program and therefore often omitted
Structural and Data Dependence
• Structural dependence– Access to a file depends on its structure• Data dependence– Changes in database structure affect program’s ability to access data– Logical data format• How a human being views the data– Physical data format• How the computer “sees” the data
Data Redundancy
• Data redundancy results in data inconsistency– Different and/or conflicting versions of the same data appear in different places• Errors more likely to occur when complex entries are made in several different files and recur frequently in one or more files• Data anomalies develop when required changes in redundant data are not made successfully
Data Anomalies
• Modification anomalies– Occur when changes must be made to existing records• Insertion anomalies– Occur when entering new records• Deletion anomalies– Occur when deleting records
Database vs. File System
• Problems inherent in file systems make using a database system desirable• File system– Many separate and unrelated files• Database– Logically related data stored in a single logical data repository
Contrasting Database and File Systems
The Database System Environment
• Database system is composed of five main parts:1. Hardware2. Software– Operating system software– DBMS software– Application programs and utility software3. People4. Procedures5. Data
DBMS Functions
• Performs functions that guarantee integrity and consistency of data– Data dictionary management• defines data elements and their relationships– Data storage management• stores data and related data entry forms, report definitions, etc.– Data transformation and presentation• translates logical requests into commands to physically locate and retrieve the requested data
– Security management• enforces user security and data privacy within database– Multi-user access control• creates structures that allow multiple users to access the data– Backup and recovery management• provides backup and data recovery procedure
– Data integrity management• promotes and enforces integrity rules to eliminate data integrity problems– Database access languages and application programming interfaces• provides data access through a query language– Database communication interfaces• allows database to accept end-user requests within a computer network environment
