Database Management System Assignment Help

A Database is a system intended to organize, store, and retrieve large amounts of data easily. It consists of an organized collection of data for one or more uses, typically in digital form. One way of classifying databases involves the type of their contents, for example: bibliographic, document-text, statistical. Digital databases are managed using database management systems, which store database contents, allowing data creation and maintenance, and search and other access

A database management system (DBMS) consists of software that operates databases, providing storage, access, security, backup and other facilities. Database management systems can be categorized according to the database model that they support, such as relational or XML, the type(s) of computer they support, such as a server cluster or a mobile phone, the query language(s) that access the database, such as SQL or XQuery, performance trade-offs, such as maximum scale or maximum speed or others. Some DBMS cover more than one entry in these categories, e.g., supporting multiple query languages. Examples of some commonly used DBMS are MySQL, PostgreSQL, Microsoft Access, SQL Server, FileMaker,Oracle,Sybase, dBASE, Clipper,FoxPro etc. Almost every database software comes with an Open Database Connectivity (ODBC) driver that allows the database to integrate with other databases.

Components of DBMS

Most DBMS as of 2009 implement a relational model. Other DBMS systems, such as Object DBMS, offer specific features for more specialized requirements. Their components are similar, but not identical.

RDBMS components

• Sublanguages— Relational DBMS (RDBMS) include Data Definition Language (DDL) for defining the structure of the database, Data Control Language (DCL) for defining security/access controls, and Data Manipulation Language (DML) for querying and updating data.
• Interface drivers—These drivers are code libraries that provide methods to prepare statements, execute statements, fetch results, etc. Examples include ODBC, JDBC, MySQL/PHP, FireBird/Python.
• SQL engine—This component interprets and executes the DDL, DCL, and DML statements. It includes three major components (compiler, optimizer, and executor).
• Transaction engine—Ensures that multiple SQL statements either succeed or fail as a group, according to application dictates.
• Relational engine—Relational objects such as Table, Index, and Referential integrity constraints are implemented in this component.
• Storage engine—This component stores and retrieves data from secondary storage, as well as managing transaction commit and rollback, backup and recovery, etc.

ODBMS components

Object DBMS (ODBMS) has transaction and storage components that are analogous to those in an RDBMS. Some DBMS handle DDL, DML and update tasks differently. Instead of using sublanguages, they provide APIs for these purposes. They typically include a sublanguage and accompanying engine for processing queries with interpretive statements analogous to but not the same as SQL. Example object query languages are OQL, LINQ, JDOQL, JPAQL and others. The query engine returns collections of objects instead of relational rows.

Description of Null Value:

NULL ,as defined above means absence of a value.A value may be absent due to two reasons:

1.Applicable value is unknown. This means value exists,but it is unknown or forgotten. That is why value is not given.

2. Value is not Applicable.That means value does not exist. So value cannot be given.

Often, the NULL value is confused with number ’0’.Actually both are completely different. A NULL is not equal to zero(0).This is because ‘0’ represents a “value” where as NULL represents “NO VALUE” or absence of a value

A best example of NULL can be found when filling up an Application Form.

Suppose,an Application Form contains a column ,”Fax Number”.Some people may possess a “Fax” and some may not have it.In this context there arises two cases.

1.Persons who possess a “Fax”,may forget the “Fax Number” and leave it blank.

2.Persons who do not possess a “Fax” also leave it blank.

In both the cases we say “Fax Number” is NULL.

Applications of Null Value:

NULL finds its applications in the field of Computer Science in the area of Database Management System(DBMS).

Database is an organized collection of logically related data.It is a collection of logically linked relations called tables, containing rows and columns. Each row is uniquely identified by a column called “Primary Key”.These tables are linked with a special column called “Foreign Key”

“Primary Key is a column or a set of columns that uniquely identify every row in a relation(table)”

The Primary key has two properties

1. It should not be NULL.This rule is called “ENTITY INTEGRITY” .

2. It must have unique value.That is , value should not repeat.

Primary key must not be NULL means ,it should not be kept empty or blank.

Some value must be provided to the Primary Key column and that value should not repeat.

Data Base Applications-advantages

1. Database management system reduces redundancy of data to a large extent because the integration and sharing of data files minimizes the chances of duplication of data.
2. Database management system controls data inconsistency because due to integration of data any changes made in one place automatically updates in all related places hence mismatch ( inconsistency ) of data is avoided or controlled.
3. Database Management system facilitates the sharing of same piece of data between various applications and users , so that they can perform different task on them.
4. Database maintains the security of data so as to prevent the unauthorised access of sensitive data in online storage .

Database Applications -

Now a days almost all the fields use database management system.Some of the database applications are as follows :

1. Encyclopedia - A database application which maintains a lot of information for various topics .
2. Library - A database application for easy transaction of references like audio CD, video CD , books etc. Accordingly it can be a CD or books library.
3. Banking - A database application which maintains information about various account holders and their respective transactions.
4. Stock Exchange - A database application which maintains information about the shares and their trade values and related operations on them.
5. Inventory Control - A database application which maintains the inventory of material and to automatically generate a sales order as per the need. It keeps checking the quantity on hand and the reorder level for generating a sales order.
6. Railways - A database application for reservation, cancellation and ticketing of passengers for railways, it also contains information about various trains and their routes & schedules.
7. Airways - A database application for reservation, cancellation and ticketing of passengers for airways, it also contains information about the schedules of planes and their routes.
8. School Management System - A database application for complete school administration like Report card generation, payroll accounting ,students administration etc.

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