1. Introduction to Databases
Overview
Objectives of this lecture.
History and Evolution of Databases.
Basic Terms in Database and Definitions of Database and DBMS.
Components of A Database System.
Characteristics, Functions and Uses of DBMS.
Limitations, Advantages and Disadvantages of DBMS.
Three aspects to study in DBMS and its Marketplace.
Preview : Database Design and Introduction to SQL.
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2. Objectives of this Lecture
Understand the evolution of databases and DBMS
Understand the limitations of file processing systems and how database management systems overcome these limitations.
Understand the concept of database management systems.
Understand the functions, uses and limitations of DBMS
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3. History and Evolution of Databases
Early computers were mainly used for scientific and engineering computation (number crunching).
However, it was soon understood that, computers could also be used to store and manipulate information. Thus, the business community where information handling is the main task, began to take interest in computers.
The first popular language for such applications, COBOL (COmmon Business Oriented Language) was developed and it soon became one of the most popular languages, second only to FORTRAN.
In early processing systems, the information was stored as groups of records in separate flat files.
These file processing systems (FPS) consisted of a few data files and many application programs written in COBOL or FORTRAN
However, business processes are dynamic, requiring continuous changes in files and applications. Any slight change in the data would require a corresponding change in the COBOL programs that uses it.
The file processing system has the following limitations.
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4. File Processing System
Application
Program
Physical
memory
File
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5. Limitations of FPS and Evolution of DBMS
No relationship between data in different files
Data Redundancy
Program – Data dependence involving file formats and access techniques
Difficulty in representing the data from the user’s view
Data Inflexibility
In order to overcome these limitations, a whole new area of Computer science called Database Applications (or simply Data Bases) evolved.
DBMS overcomes limitations
Eliminates separation and isolation of data
Reduces Data Redundancy
Eliminates dependence between Program and Data
Allows for representation of data from the user’s view
Increases Data Flexibility
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6. What is a Database Management System?
Manages very large amounts of data.
Supports efficient access to very large amounts of data.
Supports concurrent access to very large amounts of data.
Example: Bank and its ATM machines.
Supports secure, atomic access to very large amounts of data.
Contrast two people editing the same UNIX file --- last to write ``wins'' --- with the problem if two people deduct money from the same account via ATM machines at the same time --- new balance is wrong whichever writes last.
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7. Basic Terms in Database Systems
Entity: This is an object (abstract or concrete) about which information is being stored e.g., student, book, car, etc.
Field: This is an attribute of an entity. E.g., name, identification number, etc.
Record: This is a collection of related fields e.g. all the attribute of a student could constitute a record (ID number, name, major GPA, etc)
File: This is a collection of related records e.g., All records about books in a library. A file is usually arranged in a tabular form in which each row represents a record and each column represent a field.
A file organized in such a way that the records must be processed one by one from the beginning to end is called a sequential file.
In such a file, two records are separated by an inter-record gap. The end of the file is indicated by a special character called end-of-file (EOF) marker.
In contrast to sequential files, random access files (also called direct-access files) enable processing of a record without the review of other records. On the record fields is set as a key field or index.
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8. Definitions – Database and DBMS
Database: This is a collection of related files. For example, all the files that are used to store information in a library system.
Database Management System (DBMS): This is a program that allows users to define, manipulate, and process the data in a database in order to produce meaningful information
Three main components in a database system:
Physical database: This consists of the actual files comprising the database, usually arranged in some structured manner- to avoid duplication, redundancy and to ensure integrity of the data. The physical database is almost always on a disk, magnetic tape or CD-ROM
Database Management Systems (DBMS): These are programs that provide facilities for creating, accessing and maintaining the physical database. Examples of DBMS are dBASE, ACCESS & SQL Specifically, the DBMS must provide an efficient and convenient environment for users to create, add, retrieve and delete data.
Application Software: These are programs written using the facilities provided by DBMS to allow access to the physical database (or a partition of it) in a user-friendly and user-specific manner.
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9. Components of Database Management System
File
DBMS
ENGINE
Physical
memory
Application
Program
File
Operating
System
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10. Database Schema
Database Schemas: This is a logical design of a database. It consists of a set of tables of the data types used, giving the names of entities and attributes and the relationship among them.
Schemas are classified as internal – when they correspond to physical database and external when they correspond to data in application programs.
The capability to change the internal schemas as needed without affecting the external schema is called data independence.
Schemas are generally written in a data definition language which generates the schema tables stored in a file called a data dictionary.
The data dictionary is always accessed before any change to the physical data is made. The following figure illustrates some of these concept.
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11. DB System: Data Independence
Database
Schema
Users
DBMS
Data
Definition
Language
(logical)
Secondary Storage
Data
Files
Data Dictionary
(physical)
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12. Characteristics, Functions and Uses of a DBMS
It is a computerized record-keeping system.
It contains facilities that allow the user to . . .
Add and delete files to the system.
Insert, retrieve, update, and delete data in existing files.
It is collection of databases.
A DBMS may contain many databases that can be used for separate purposes or combined to provide useful information.
Functions :
To store data
To organize data
To control access to data
To protect data
Uses :
To provide decision support Managers and analysts retrieve information generated by the DBMS for inquiry, analysis, and decision-making.
To provide transaction processing Users input, update, and process data with transactions that generate information needed by managers and other users or by other departments.
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13. Advantages and Disadvantages of a DBMS
Centralized Data reduces management problems.
Data redundancy and consistency are controllable.
Program - data interdependency is diminished.
Flexibility of data is increased.
Disadvantages:
Reduction in speed of data access time.
Requires special knowledge.
Possible dependency of application programs to specific DBMS versions.
Application Languages need specific interface (Drivers) to interact with DBMS
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14. Three Aspects in DBMS and its Marketplace
Three Aspects to Study in DBMS:
Modeling and design of databases.
Allows exploration of issues before committing to an implementation.
Programming: queries and DB operations like update.
SQL = ``intergalactic dataspeak.''
DBMS implementation.
The DBMS Marketplace:
Relational DBMS companies --- Oracle, Informix, Sybase --- are among the largest software companies in the world.
IBM offers its relational DB2 system. With IMS, a non-relational system, IBM is by some accounts the largest DBMS vendor in the world.
Microsoft offers SQL­Server, plus Microsoft Access for the cheap DBMS on the desktop, answered by ``lite'' systems from other competitors.
Relational companies also challenged by ``object­oriented DB'' companies.
But countered with ``object­relational'' systems, which retain the relational core while allowing type extension as in OO systems.
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