Presentation

On Computer Database

1

DatabaseObjectives of this session•What is a Database?• Where and when we need to use

Databases• Types of users in a Database• Database Design

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Objectives Cont..

•Database Management Systems, Database Operations and SQL

• Database Security

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• Database is a collection of data organized to service many applications at the same time by storing and managing data so that they appear to be in one location.

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What is Database

Application of Databases•   Banking: For customer information, accounts, and

loans, and banking transactions.

•    Airlines: For reservations and schedule information.

•    Universities: For student information, course registrations, and grades.

• Credit card transactions: For purchases on credit cards and generation of monthly statements.

•  Telecommunications: For keeping records of calls made, generating monthly bills, maintaining balances on prepaid calling cards, and storing information about the communication networks.

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•  Finance: For storing information about holdings, sales, and purchases of financial instrument such as stocks and bonds.

• Sales: For customers, product, and purchase information.

•  Manufacturing: For management of supply chain and for tracking production of items in factories, inventories of items in warehouses/stores, and orders for items

• Human resources: For information about employees, salaries, payroll taxes and benefits, and for generation of paychecks.

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Data Hierarchy

The data hierarchy comprises: bits, bytes, fields, records, files, and database.

Bit: Smallest unit of data represented by 1 or 0.

Byte: A group   of 8 bits

Field: Unit of data consisting of one or more characters. For example id, name, address.

Record: A collection of related fields

File: A collection of related records

Database: A collection of related files

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Disadvantages of traditional file system

• Data redundancy: Same information may be duplicated in several places.

•  Inconsistency: The various copies of same data may no longer agree 

• Difficulty in accessing data: Conventional file-processing environments do not allow needed data to be retrieved in a convenient and efficient manner.

• Data isolation: Data are scattered in various files, and files may be in different formats.

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•    Integrity problems

Data values stored in the database must satisfy certain types of consistency constraints. It is difficult to satisfy these constraints in traditional file system.

• Atomicity problems

It must happen in its entirety or not at all. It is difficult to ensure atomicity in a conventional file-processing system.

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•   Concurrent-access anomalies

Concurrent accessed needed for performance

• Uncontrolled concurrent accesses can lead to inconsistencies

•Example: Two people reading a balance and updating it at the same time

• Security problems

• Hard to provide user access to some, but not all, data

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File OrganizationFile organization deals with the physical organization of

the records of a file for the convenience of storage and retrieval of data records.

Sequential file organization: A method of storing data records in which the records must be retrieved in the same physical sequence in which they are stored.

Advantages: 1. Simple 2. Easy to organize 3. Requires inexpensive storage media

Disadvantage: 1. Inefficient for application 2. Slow

Random file organization: Allows users to access records in any sequence without regard to actual physical order on the storage media.

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Advantages: 1. Can be retrieved quickly

2. Need not be sorted 3. Support interactive online applications

Disadvantages: 1. Requires expensive hardware 2. Not suitable for sequential processing

Indexed Sequential file organization: A method to directly access records organized sequentially using an index of the key fields.

Advantages: 1. Efficient for sequential processing 2. Also suitable for random access processing

Disadvantages: 1. Requires expensive hardware 2. Requires more storages

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Database-Management System

• A database-management system (DBMS) is a collection of interrelated data and a set of programs to access those data.

Three Components

• Data-Definition Language (DDL)

• Data Manipulation Language (DML)

• Data Dictionary

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DDL• We specify a database schema by a set of definitions

expressed by a special language called a data-definition language (DDL). For instance, the following statement in the SQL language defines the account table:

Create table account(account-number char(10),balance integer)

Execution of the above DDL statement creates the

account table.  In addition, it updates a special set of tables called data dictionary or data directory. A data dictionary contains metadata-that is, data about data.

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DMLDML

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Data manipulation is Data manipulation is

•• The retrieval of information stored in the databaseThe retrieval of information stored in the database

•• The insertion of new information into the database The insertion of new information into the database •The deletion of information from the databaseThe deletion of information from the database•The modification of information stored in the databaseThe modification of information stored in the database

A data-manipulation language (DML) is a language that enables users to access or manipulate data as organized by the appropriate data model.

•Example: SQL (Structured Query Language)

QBE (Query By Example)

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Example of an SQL

SELECT id, name FROM student WHERE id=10

Execution of the above SQL statement display the student information with id value equal to 10.

Data Dictionary

Data dictionary is an automated or manual tool for storing and organizing information about the data maintained in a database.

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View of Data

• Data Abstraction:

A major purpose of a database system is to provide users with an abstract view of the data. That is, the system hides certain details of how the data are stored and maintained.

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Levels of Abstraction• Physical level: describes how a record (e.g.,

customer) is stored.

• Logical level: describes data stored in database, and the relationships among the data.

type customer = record

customer_id : string; customer_name : string;customer_street : string;customer_city : integer;

end;

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Fig: Relationship among three levels

• View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security purposes.

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An architecture for a database system

Database Models/ Types of Database Organization

Principal database models are

• Hierarchical Model / Database

• Network Model / Database

• Relational Model / Database

• Entity-Relationship Model / Database

• Object-Oriented Model / Database

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Hierarchical Data Model

• Hierarchical data model is one type of logical database model that organizes data in a treelike structure. A record is subdivided into segments that are connected to each other in one-to-many parent-child relationships.

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Employee

Compensation Benefits

Performance

JobAssignments

Salary History Insurance HealthPension

Network Data Model

• Network data model is logical database model that is useful for depicting many-to-many relationships.

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Course 2Course 1 Course 3

Student 1 Student 2 Student 4Student 3 Student 5

Relational Data Model• Relational data model is a type of logical database model

that treats data as if they were stored in two-dimensional tables. It can relate data stored in one table to data in another table as long as the two tables share a common data elements.

• A tuple is a row or record in a relational database.

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IDID NameName

11 AAAA

22 BBBB

IDID MarksMarks GradeGrade

11 7070 B+B+

22 8080 A+A+

STUDENT RESULT

Object Oriented Data Model

• An object Oriented database is an approach to data management that stores both data and the procedures acting on the data as objects that can be automatically retrieved and shared.

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Security

The data stored in the database need protection from unauthorized access and malicious destruction or alteration, in addition to the protection against accidental introduction of inconsistency that integrity constraints provide.

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