Database Management PDF

 DATABASE MANAGEMENT Chapter 1 Introduction to Database Systems Contents Data Information Data Processing Manual File-based System File Processing System Database Database Management System (DBMS) Relationship between DBMS & Application Program Brief History of Database S...

 DATABASE MANAGEMENT Chapter 1 Introduction to Database Systems Contents Data Information Data Processing Manual File-based System File Processing System Database Database Management System (DBMS) Relationship between DBMS & Application Program Brief History of Database Systems Data Chapter 1 - Introduction to Database Systems  Data Word "Data" is plural of "Datum" means a single piece of information, statistic, or code Data A collection of raw facts and figures related to an object Object  a person, an organization, an event, or any other thing that is significant in a system Data may be in form of text, numbers, images, sounds, and videos Collected for different purposes Processed to produce meaningful information reports, charts, and web pages, etc. In an organization, data is as important as blood in human body Gives a view of current and past activities History related to rise and fall of an organization  Data Example May be collected to prepare the result of an examination of students Unprocessed data of students In raw form These facts satisfy the definition of data but these facts (i.e. data) are useless in this form To completely understand  must be processed according to requirements in a system  Structured Data & Unstructured Data Structured Data  data in form of numbers, characters, and dates Example: data of class students Includes facts such as students' roll numbers, names, addresses, and telephone numbers This data is in numeric and characters form Unstructured Data  facts of an object or event may be in the form of photographic images or maps, sound, and video Example: photos of all class students are collected and stored on a media such as a disk These days  structured and unstructured data are often collected for different purposes For example: Database of college students collects names, addresses, telephone numbers, and photos of all students  Qualitative & Quantitative Data Data can be qualitative or quantitative: Qualitative data  descriptive information Describes something; it can be observed but cannot be measured Examples Mr. Saqib has a white color This cat is very soft This painting shows some masterful brush strokes, etc. Quantitative data  numerical information (numbers) Divided into: discrete data & continuous data Discrete data  counted, only take certain values like whole numbers Mr. Saqib has 4 brothers and 2 sisters Continuous data  measured, take any value within a range Today temperature has increased up to 34.5 OC The car is running with speed between 80 to 100 kilometers per hour On heating this object, its volume increases up to 5%, etc  Types of Data 1) Numeric Data Consists of digits from 0 to 9, +, and - signs and decimal point Examples: 4020, 3.543, -7.2, and 1302 Integer data  consists of positive or negative whole values including 0 Examples: 1302, +62, and -26 Real data  consists of values that have decimal point Examples: 15.4,.006, 4.07, -6.27, and 4.0 2) Alphabetic Data consists of all alphabet letters from A to Z, a to z, and blank spaces Examples: Iqra Aslam, Pakistan, Asia, etc. 3) Alphanumeric Data consists of alphabets (both capital and small letters), numeric digits (0 to 9), and special characters or symbols such as #, $, etc. Examples: 23-March 1940, 28-May 1998, F–16, etc.  Types of Data 4) Image Data consists of charts, graphs, pictures, and freehand drawings Also represented by bit patterns Transmitted as contiguous bits 5) Audio Data consists of recordings of conversations, music, speeches, or any other type of sound continuous and not discrete in the form of continuous voice signals Converted into digital form before entering it into the computer 6) Video Data consists of video recordings of events Consists of full-motion images that create actions and movements Can be produced by a video camera, animation application, or movie-maker software, etc. Information Chapter 1 - Introduction to Database Systems  Information An organization collects and stores data from both internal and external sources Usually, collected data is not in proper format and does not give proper meanings Various operations are performed to get the required results that give proper and useful meanings  information Information  processed data used for decision-making, analytical purposes, and fault diagnosis, etc. processed using various techniques Input  Data Processing Output  Information  Information Students’ data can be analyzed and summarized using different tools Can also be presented in graphic form Can sort records based on their names, marks, disciplines, districts or regions, grades, and ages, etc. Processed data now gives a clear and proper understanding of student names, obtained marks in different subjects, total marks obtained, and grade of each student To calculate total marks of a student, Data  marks obtained in different subjects Information  calculated "Total Marks" To find out grade of students, Data  calculated "Total Marks“ Information  "Grade" Data Processing Chapter 1 - Introduction to Database Systems  Data Processing Process of converting data into meaningful information Different operations are performed on data to convert it into information Editing, verification, and conversion of data into acceptable formats Updating of data, as technologies change with the passage of time Classification of data Restructuring, reorganization, and analysis/modeling of data, etc. Depending on the procedures and equipments used Ways of processing data Manual data processing Mechanical data processing Electronic data processing  Manual Data Processing data is processed manually without using any machine or tool data is transferred manually from one place to another Slow data processing and errors may occur In Pakistan  data is still processed manually in some small business firms government offices Institutions Example: A clerk in a college performs tasks at end of the month on his register with the help of a pen or pencil Find out total number of students that have paid fees Find out total number of students that have not paid fees Calculate total amount collected as fees from students Calculate total amount of salary drawn by the staff at that month  Mechanical Data Processing data is processed using different mechanical devices Mechanical devices  typewriters, calculators, or other mechanical devices Fast data processing and more accurate Example: In manual data processing  clerk performs all tasks by hand Very difficult and time-consuming method If performs by calculator easy process and will be completed in a very short time  Electronic Data Processing Refers to the use of automated methods to process data All operations on data are performed using computer & software Input  data and set of instructions computer automatically processes the data according to given set of instructions Computer  electronic data processing machine Fast and accurate method In computerized education environment  results of students are prepared through computer applications In banks  accounts of customers are processed and maintained through computer software, etc. Example: Clerk  Search record from more than 1000 students Students that have aged more than 18 and less than 22 Students that have passed all subjects Result of all students of a class in a particular subject etc. Difficult to perform these tasks by using manual or mechanical data processing Can be performed very easily and quickly by using computer applications Manual File-based System Chapter 1 - Introduction to Database Systems  Manual File-based System Oldest system used for records keeping in an organization A set of books (or files) is prepared Each book or file holds a particular set of information Each department of the organization has a separate file (or set of files) for every significant task Information is shared among different departments through files Many such files are labeled and placed in one or more cabinets Security  cabinets are locked or may be located in secure areas of the building Example: college’s manual file-based system for maintaining records of students and courses of different faculties etc. Students record file  used to store records of each student Students fee file  used to store fee records of students Students result file  used to store the result of examinations of students Students course file  used to store data of courses taken by students  Manual File-based System Decentralized approach is adopted where each department processes and controls its own data - Very slow method to process data - because data is analyzed and computed manually - data is transferred from one department to another manually - Very costly method - because large number of employees have to be appointed to operate the file- based system - Managers cannot easily obtain summary information required for making decisions - Large space is needed to store the files/books - Also difficult to search a specific file or a piece of information - Duplication of data may exist throughout the organization - Multiple chances of errors - Chances of physical damages to files (i.e. cutting, wetting, and burning) File Processing System Chapter 1 - Introduction to Database Systems  File Processing System To understand characteristics of a pure database system necessary to know about file processing system Collection of files and programs that store, access, modify and manage data in these files Computer file processing system or traditional file processing system or computer file-based system In early days of computer  no databases Data was stored in computer files on tape or disk stored and managed  through file-processing system Still used in some small organizations  File Processing System Each department has its own set of data files Each application program is developed with its own set of data files Example "Student.dat"  created and maintained in admission office used by "Admission" program also forwarded to registrar’s office "Course.dat"  created in registrar’s office contains information about courses of different subjects "Course.dat" + “Student.dat"  used by "Schedule" program to generate individual student schedules and class lists "Pay.dat“  has information required for calculating pay and preparing payroll sheets used by "Payroll" application program used to create payroll of the employees  Disadvantages of File Processing System - Data Redundancy means multiple copies of same data File processing system  each application program has its own set of data files Same data may exist in multiple files Problems of duplication of data To update specific data/record  same data must be updated in all files; otherwise different files may have different information about a specific record Valuable storage space is wasted due to duplication of records For example, in university environment "student.dat“ of admission office  roll numbers, names, and addresses, etc. "result.dat“ of registrar’s office  roll numbers, names, addresses, obtained marks of subjects, and results of all the examinations, etc. both files contain roll numbers, names, and addresses of the students Same data is stored in multiple files  Disadvantages of File Processing System - Data Inconsistency means that different files may contain different information about a particular object or person Redundancy leads to inconsistency When same data is stored at multiple locations  inconsistency may occur Example Address of a student is updated at "result.dat“ of registrar’s office data files are maintained by other departments also some data files may contain old address, while others contain new address - Data Isolation Computer file-processing system  data is stored (or isolated) in various files becomes very difficult to access desired information from data files For example "student.dat“ stores addresses of students "result.dat“ stores examination marks Need data from both files Difficult job with computer file processing Programmer must write a new program to extract required data from both data files  Disadvantages of File Processing System - Data Atomicity Transaction  collection of all the steps required to complete an operation on data Atomicity  means that either one transaction should take place as a whole or it should not take place at all Suppose want to transfer amount of Rs.15000/- from account X to account Y Step-1: Deduct amount of Rs.15000/- from account X Step-2: Add amount of Rs.15000/- to account Y If system fails (e.g. due to power failure) after Step-1 amount of Rs.15000/- has been deducted from account X but has not been added to account Y data atomicity problem  occurs in transaction-based file processing systems i.e. banking - Program Data Dependency Program data dependency  relationship between data stored in a file and specific program required to process that file File processing system  data stored in a data file depends upon the application program through which data file was created Structure of data file is defined in application program Difficult to change the structure of data file If data file changed  modify application program also  Disadvantages of File Processing System - Difficult Program Maintenance File-processing system  program maintenance is difficult data file depends upon application program Any modification in data file (size & data type of data field)  requires redesigning application program Organization has to pay a lot of money for maintenance of program - Limited Data Sharing File processing system  each application program uses its own data files Difficult to access data from a data file created by another application program Provides very limited facilities to share data among multiple users - Security Problem File processing system does not provide proper security against illegal access to data files In most situations  different levels of security is required for different groups of users Customers should be allowed to only view and purchase products Sales Persons should be allowed to enter sales data along with view facility to view products Sales Officer should have the facility to modify or delete the sales data also File processing system does not provide such types of advanced security options Database Chapter 1 - Introduction to Database Systems  Database Database is an organized collection of related data stored in an efficient and compact manner word "organized"  means that data is stored in such a way that it can easily be accessed and updated phrase "related data“  means that a database contains data or information about a particular area such as: Database of employees that contains data of employees of an organization or department Database of students that contains data of students of a college/university etc. word "efficient“  means that required data can be searched very easily and quickly word "compact“  means that stored data takes up as little space as possible without any duplication of data  Examples of Databases NADRA In Pakistan, NADRA maintains a database having information of all citizens of Pakistan Record of any citizen of Pakistan can be accessed very easily and quickly through CNIC #. Library In local library  computerized database containing details of books in library Computerized index (automated catalog), which allows to find a book with reference to its title, or its author’s name, etc. College/University Database containing information about the present and previous students Bank Accounts When withdraw amount through ATM card  accessing a database of customers of a particular bank Bank account accessed through Auto Teller Machine (ATM) After withdraw  bank record is updated through a software application immediately E-mail Accounts Popular websites "hotmail.com", "gmail.com" and "yahoo.com"  contain online databases Having free e-mail accounts of users all over the world Manual and computerized databases Manual Database  library card catalog Computerized database created and maintained by a set of programs (database management system)  Database Table Database contains various objects used for different purposes Most important object  "table“ Database may consist of many tables Data stored in tables Table is made up of columns and rows Rows represent records Each row is divided into columns called fields Fields contain different data values of a particular record  Metadata Database holds related data + description of that data database is also defined as  a self-describing collection of integrated records Description of data  metadata or system catalog or data dictionary Metadata  data about data When table is designed  data type, size, format, and other descriptions of fields are specified Metadata of the table Metadata describes properties or characteristics of actual data in database Describes logical structure of database field names i.e. data item names data type of each data item length or width of data items rules and constraints about data a brief description of each data item Helps database designers and users to understand data in database Metadata is saved in a data dictionary file Consulted before actual data is read or modified in the database DDL (Data Definition Language) is used to define metadata It defines a data dictionary of tables in the database  Types of Database Types based on databases architectures Centralized Databases Personal computer databases Client/Server databases Distributed Databases Homogeneous databases Heterogeneous databases Object-Oriented Databases  Centralized Databases All data (complete database) is stored and maintained in one location Location is most often a central computer or a server Data is managed, updated, and accessed at the central site Multiple users can access centralized database Centralized database systems are mostly used in colleges, banks, hospitals, and small organizations Examples of centralized databases Personal computer databases Client/Server databases  Centralized Databases Personal Computer Databases Normally created and maintained by a single user on his/her personal computer Commonly used in small businesses or organizations Used for simple accounting, inventory management, and customer billing systems, etc. Relatively simple to develop and use - data cannot easily be shared among different users Client / Server Databases client/server architecture is used in which one computer acts as a server for storing all data, while clients access data Server  includes software called DBMS and a computer provides back-end functions requested by clients Back-end functions  database management, communication management, printing, etc. Clients  provide front-end functions send requests to server and receives results from server  Centralized Databases Client / Server Databases Objective  to allow multiple users in network to access or share data Usually, the database processing functions are performed on database server Often used for work-group computing More secure than central computer databases server computer allows access to database to only authenticated users on client computers  Centralized Databases Client / Server Databases +Data integrity is maximized and data redundancy is minimized +Data can be accessed by many users simultaneously +Easier to maintain and keep updated +Since all data are stored in a single location +Easier to create a backup of data +Helps in maintaining of data in an accurate and consistent state +Also enhances data reliability +Gives strong and centralized security i.e. data in a centralized database is always secure +Easier for use to end-users due to its simplicity of being a single database design +Provides data portability and better database administration +More cost-effective (i.e., cheaper) than other types of database systems as maintenance costs are always minimum +Keeping data at a single location is easier to change, re-organize, and analyze +Updates to any given set of data are immediately received by every end-user  Centralized Databases Client / Server Databases - Since all data is at one location, takes more time to search and access - If network is slow, this process takes even more time - A lot of data access traffic, may create a bottleneck situation - data accessing from database becomes very slow down, So data availability is not as efficient as in a distributed database - Most of them are highly dependent on network connectivity. Due to slower network connection (i.e. internet connection), a problem to access the database is created - In case of any hardware failure  data availability within the entire network will be affected - If there is any problem in central site  complete database system fails - If a set of data is accidentally lost  difficult to retrieve it back - Deadlocks can occur while attempting to update shared tables that are already in use - Needs trained and experienced staff for its administration  Distributed Databases Data is stored across different physical locations portions of a database are physically distributed across different sites or locations in a computer network System administrator can distribute collections of data across multiple physical locations Can reside in network servers on Internet, on corporate Intranets or Extranets, or other company networks Managed by a centralized distributed database management system (DDBMS) Access data through a computer network Some big and multi-national organizations/departments use distributed databases Processes to keep a distributed database up to date Replication  process identifies changes in the distributed database Once changes have been identified  replication process applies those changes to make sure that all distributed databases look same Complex and time-consuming process depending on size and number of distributed databases Require a lot of time and computing resources Duplication  process identifies one database as a master database and duplicates that database at different locations Not complicated process but it makes sure that all distributed databases have same data users may change only master database Ensures that local data will not be overwritten  Distributed Databases Homogeneous Databases means that database technology is same at each of the locations (or sites) Data at various locations are also compatible All nodes use same hardware and software for the database system Comparatively easier to design and manage Conditions must be satisfied Operating system used at each location must be the same or compatible Data structures used at each location must be the same or compatible Database application (or DBMS) used at each location must be the same or compatible  Distributed Databases Heterogeneous Databases Different sites or locations may have different hardware and software Data structures at various sites are also incompatible Different computers, operating systems, and database applications (or data models) may be used at each of locations For example one location  have latest relational database management technology Another location  store data using a network database or an old version of the DMBS One location  have Windows NT operating system Another location  have the UNIX Usually used when individual sites use their own hardware and software Translations are required to allow communication between different sites Users must be able to make requests in a database language at their local sites Usually, SQL database language is used A user at one location may be able to read but unable to update data at another location Often not technically or economically feasible Distributed Databases Heterogeneous Databases +Local data management - Complexity +Improved performance - Higher cost of installation +Reliability and and maintenance availability - Security +Modularity - Difficult to maintain integrity +Protection of data +Independence - Lack of standards + Low Communication - Database design more Cost (More Economical) complex Note: Details are given in PM series book  Object-Oriented Databases Object Database Management Systems (ODBMS) Store objects rather than data like integers, strings, or real numbers Objects are used in object-oriented languages such as Smalltalk, C++, Java, Visual Basic.Net, Delphi, Ruby, etc. Objects consist of Attributes  defines characteristics of an object May be simple such as integers, strings, and real numbers or it may be a reference to a complex object Methods  define behavior of an object; formally called procedures or functions Objects  executable code + data Characteristics of objects  whether methods or data can be accessed from outside object Another term is classes Used in object-oriented programming to define object’s data and methods like a template for object does not itself contain data or methods but defines data and methods contained in object used to create object may be used in object databases to re-create parts of the object that may not actually be stored in database Methods may not be stored in database and may be re-created by using a class  Object-Oriented Databases Comparison of Object Database with Relational Databases Relational databases  stores two dimensional tables (rows and columns) All table columns depend on a primary key (a unique value in the column) to identify column Once specific column identified, data from one or more rows associated with that column may be obtained or changed To put objects into relational databases  must be described in terms of a simple string, integer, or real number data For instance  in case of an airplane wing may be placed in one table with rows and columns (describing its dimensions and characteristics) propeller in another table, tires in another, and so on. Uses of Object-Oriented Databases used when there is complex data and/or complex data relationships Includes a many to many object relationship Should not be used when there would be few join tables & large volumes of simple transactional data Applications CAS Applications such as CASE-computer aided software engineering, CAD-computer aided design, and CAM-computer aided manufacture Multimedia Applications Object projects that change over time Commerce  Object-Oriented Databases +Objects don't require assembly - Lower efficiency when data is and disassembly saving coding simple and relationships are time and execution time to simple assemble or disassemble objects +Easier navigation - Relational tables are simpler +Better concurrency control - Late binding may slow access speed +A hierarchy of objects may be locked - More user tools exist for +Data model is based on the real RDBMS world - Standards for RDBMS are +Works well for distributed more stable architectures - Support for RDBMS is more +Less code required when certain and change is less applications are object-oriented likely to be required Database Management System (DBMS) Chapter 1 - Introduction to Database Systems  Database Management System (DBMS) A collection of programs that are used to create, maintain, and extract data from databases A general-purpose software Often called database software Different types of DBMSs are available, ranging from small systems that run on personal computers to huge systems that run on mainframes We can also develop a special purpose DBMS software (in Visual Basic, C++, etc.) to create and maintain specific databases Functions of DBMS Defining the Structure of Database Populating the Database Manipulating the Database Parts of DBMS Physical Database  consists of a file or set of files that contain data Database Engine  part of DBMS that makes it possible to access (store and retrieve data) and modify data  Database Management System (DBMS) Examples of DBMS Microsoft Access Oracle Microsoft SQL Server MySQL FileMaker Pro Components of a DBMS Environment Software Hardware Data Procedures Users  Components of a DBMS Environment 1. Software Set of programs used to manage database and to control overall computerized database system DBMS Software Manages the database within database system Operating System Manages all hardware components and makes it possible for all other software to run on the computers Application programs & Utilities To access and manipulate data May be conventional or online services Utilities  software tools used to manage computer environment in which data access and manipulation take place Network Software Used in network to share data of database among multiple users  Components of a DBMS Environment 2. Hardware Set of physical electronic devices on which DBMS is implemented Consists of computers, storage devices, I/O channels, electromechanical devices In a network, a powerful computer with very high data processing speed and storage device with large storage capacity is required as a database server 3. Data Databases are defined, constructed and then data is stored, updated, and retrieved to and from databases Database contains both actual (or operational) data and metadata (data about data or description about data) 4. Procedures The instructions and rules that help to design database and to use DBMS Users who operate and manage DBMS require documented procedures to use or run DBMS Purpose of procedures to setup and install the new DBMS to login and logout of DBMS software to manage DBMS or application programs to take a backup of the database to handle hardware and software failures to change the structure of the database  Components of a DBMS Environment 5. Users People who use and manage databases Perform different types of operations on databases Application Programmers Users who write application programs in different programming languages to interact with databases Programming languages  Visual Basic, Java, or C++ End-users use application programs written by application programmers Examples: software used in libraries, shopping stores, and medical stores Designs a user-friendly interface of program so that end-users can use easily and efficiently Database Administrator Person who manages overall database management system  DBA Responsibilities of DBA Installing and managing DBMS Creating databases and related objects like tables and indexes Authorizing access to database Coordinating and monitoring DBMS Acquiring software and hardware resources as needed Security and integrity control Maintenance of the operational system Creating a backup of data regularly Recovery of a database in case of failures in online access of data required by the other users  Components of a DBMS Environment 5. Users End-Users People who interact with DBMS to perform different operations on database Operations  retrieving, updating, inserting, deleting data etc. Access DBMS through application programs interface, IDE provided by DBMS or SQL interface Interface is provided as an integral part of DBMS Such interfaces are also supported by means of online applications to interact with online databases from online workstations or terminals Casual End-Users Sophisticated users  trained persons who know structure of database and facilities offered by DBMS Normally use standard query languages such as SQL to perform required operations Some sophisticated end-users may even write application programs for their own use Naive Users They do not know structure of database or any query language They do not have any technical knowledge of DBMS Access databases through application programs (or IDE) Access data by selecting options from menus or by entering simple commands For example: in a university registrar’s office, Naive user  clerk Casual user  registrar’s data processing operator  Database Approach +Controlling Data Redundancy - Higher Cost of Hardware and Software +Data Consistency +Data Sharing - Higher Cost of Data Conversion +Data Integration +Data Integrity - Cost of Staff Training +Data Security - Technical Staff +Data Atomicity - Database Failures +Control over Concurrency +Backup and Recovery Procedures Note: Details are given in PM series book +Data Independence Database Management +Less Storage (or Compactness) Systems, PM series by CM +Advanced Capabilities (Online Aslam & Aqsa Aslam access)  File-Based Approach Database Approach Data redundancy is not controlled Data redundancy is controlled Data may be inconsistent Data is always consistent Data stored in data files are Data stored in database files are dependent on application programs independent of application programs Data sharing among multiple users centralized data  can easily be is difficult shared among multiple users Data atomicity problem may arise No data atomicity problem Does not provide proper security against illegal access to data Provides proper security against Related data may be stored in many illegal access to data data files All related data is stored in a single No Integrity consistency rules  database file correct data may not be entered Integrity consistency rules applied into data files correct data can be entered No control over concurrency Gives full control over concurrency Very simple system Very complex system Cost is less than database system Cost is much more than file system Relationship between DBMS & Application Program Chapter 1 - Introduction to Database Systems  Relationship between DBMS & Application Program Very close relationship between the DBMS and the application program Application program  provides user-interface to perform different operations on the database via DBMS User sends requests to DBMS DBMS receives requests & processes and returns results to application program User receives results through application program For example DBMS retrieves data from database or performs other different operations on database according to requests sent by the user Application program  front-end Database  back-end Brief History of Database Systems Chapter 1 - Introduction to Database Systems  Brief History of Database Systems Concept of database was first introduced in 1960s Hierarchical DBMS Research conducted during 1960s Results in GUAM (Generalized Update Access Method) developed by NAA (North American Aviation) GUAM was based on concept that smaller components come together as part of larger components until the final product is assembled Like a hierarchical structure 1968  IBM developed a system known as IMS (Information Management System) IMS was first commercially available database system (DBMS) Based on hierarchical file system, which was built by NAA Network DBMS Mid-1960s  IDS (Integrated Data Store) General Electric Company developed a database system based on network data model First network database system Considered superior to hierarchical database system Data Base Task Group (DBTG) Formed by Conference on Data Systems and Languages (CODASYL) to develop a set of standards for network database system  Brief History of Database Systems Relational Database Systems 1970  Paper published by E. F. Codd, an IBM Researcher Title: "A Relational Model of Data for Large Shared Data Banks“ Introduced relational data model for managing data Used concepts of a branch of mathematics called relational algebra to suggest a model of shared data banks DB2 IBM started working on Dr. Codd’s concepts Introduced relational language SQL and relational database system  DB2 Today, SQL is most widely used relational language Relational database management system (RDBMS) is based on relational model introduced by E. F. Codd Today most popular and commonly used PC-based relational DBMS products  Oracle and MS-Access  Brief History of Database Systems Client-Server Database Applications Earlier multi-user architectures used mainframe computers to process database Mainframe computer provides all functions to connected users directly contains DBMS software, application programs, and user-interfaces Users were connected through their terminals Remote users were connected to mainframe in a communication network Mid-1980s  most users began to share data through a LAN Microcomputers were linked together in a LAN LAN enabled users to send data to one another through computers First application of LAN enabled users to share resources and to communicate via electronic mail End-users also wanted to share their database led to the development of multi-user database applications on LANs After this, Client-Server architecture was introduced  Brief History of Database Systems Database Processing on the Internet 1969  Internet was introduced by Advanced Research Projects Agency (ARPA) of USA Today, most of database systems are online Databases, DBMS software, and database applications are stored on Web server Database technology + Internet technology  to access data on Web server Database on Internet uses hypertext transfer protocol (HTTP), dynamic hypertext markup language (DHTML), and extensible markup language (XML) to communicate between database application and database stored on Web server Object-Oriented Database Systems Mid-1980s  become clear that there were several fields where relational databases were not applicable, due to the types of data involved E.g. medicine, multimedia, and high-energy physics, all of which needed more flexibility in how their data was represented and accessed Led to research being started in object-oriented databases where users could define their own methods of access to data and how it was represented and manipulated Beginning of 1990s  Object-Oriented DBMS (OODBMS) & object-relational DBMS (ORDBMS) Unlike previous models  actual composition of these models is not clear This evolution represents a third generation DBMS For more details, refers to PM Series Database Management by CM Aslam, Aqsa Aslam, Mudassir Ahmad & Hafiz Saeed Ahmad Publisher: Majeed Sons 22- Urdu Bazar, Lahore