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Saturday, June 14, 2014


An organization must have accurate and reliable data for effective decision-making. For this, the organization maintains records by combining the data from different sources in an organization. Database is a collection of related information stored along with the details of interpretation of the data contained. For managing the data in the database we need a system called Database Management System. In other words, DBMS is a complex piece of software that facilitates a flexible management of the data. Through DBMS we can access, monitor, store and modify the database. Through DBMS data can be made available to all users and redundant (duplicate) data can be minimized or completely eliminated.  

DBMS also makes possible for an organization to prevent important data access from unauthorized users by providing the security to the database at different levels. Some of the DBMS that are used are INGRES, ORACLE, SQL Server and SYBASE. The DBMS allows users to access data from the database having no knowledge of how data is actually stored in it. The process is much the same as ordering a menu in the restaurant. A customer simply orders for the food to a waiter and waiter serves the specified order. A customer only checks the menu for the desired items and need not know how the items are arranged in a restaurant. Similarly, the database user need not know how the data is stored instead he needs to know only what he requires and the DBMS takes care of retrieving the required data on its own. 

Let’s look into the components of DBMS: 

DML Precompiler (Data Manipulation Language Precompiler): As its name
specifies, this is a compiler that converts DML statements (Statements that allows the users to manipulate the database) in an application program into normal procedure calls in the host language. This precompiler must interact with the query processor (discussed later) in order to generate the appropriate code.

DDL Compiler (Data Definition Language Compiler): The DDL compiler converts the data definition statements (statements that define the tables, database etc.) into a set of tables. These tables contain information in the form that can be used by other components of the DBMS.

File Manager: File manager manages the structure and space of the file on disk. This also locates the block in which the required record exists and requests from the disk manager for this block containing the required record and finally provides the required record to the data manager.

Disk Manager: As specified earlier, disk manager provides the block or page that the file manager asks for. The disk manager is a part of Operating System. Disk Manager does all the physical input and output operations.

Data Manager/Database Manager: It is also called database control system. It is a software component of the DBMS or we can say a program module that acts as an interface between the data stored in the database and the queries submitted to the system. Data Manager converts the queries from the user into the file system. It is actually responsible for the storage, retrieval and manipulation of the data in the database. Besides these responsibilities data managers also takes care of maintaining integrity. This means that the appropriate data should be stored in the database. For example, date of joining of an employee should not be less than the current date or the age of an employee for a particular post should lie between 25 and 40. If these constraints are specified in the database, then database manager takes care of them on its own. Database Manager also checks for an unauthorized user accessing the database. Database Manager does not allow any user to access the database without having the permission granted.

Query Processor: The Query Processor takes care of the queries by the database user. The database user when uses the Data Manipulation Language (DML) for retrieving the data, the Query Processor converts it into that form that could be sent to the Data Manager, so that Data Manager can execute it.

Data Dictionary: A data dictionary contains the information/ data about the data. A data dictionary includes all the database descriptions, entity/ table descriptions, attributes etc. Apart from these data dictionary includes the information about the users also, which tables are used by which programs, authorization of users. A data directory/ dictionary is just like a database and its cost depends on how complex it is? More complexity leads to increase in cost. Just like an index helps us to find the chapter easily, data dictionary helps DBA for designing, implementing and maintaining the database and searching for the desired record in the database. It also helps the managers and end users in their project planning. 


In database system, for storing the data, each column in the table have a certain type of data. For example when we create a table for employee’s personal data, then we may have different fields like name, address, phone, age etc. In this if we take the field “name” then this would of character type and “age” and “phone” are of numeric type. 

Sometimes an attribute of a table T takes the values from a set D that is known as a domain. A domain is defined in the cases when we want an attribute to take some exact set of constants. For instance, the domain of the attribute age for a particular post that a candidate can apply for, might be defined as consisting of all the integer numbers between 18 and 25. On the other hand, the domain of the marks column, might be defined as all the numbers between 0 and 100, with at most one non-zero digit after the decimal point (assuming the maximum marks to be 100). The significance of declaring a column of a table to have a particular type (or domain) is the ability to compare the values of two different column rests on this declaration. A particular column I a table must contain similar data, which is of a particular type. Besides storing character, numeric, we can also store data, binary data such as graphics, sound also. Whenever we have the bio data of employees or students or candidates, sometimes it is nice to store their photographs also, in that cases, we can use graphics as a data type for photograph column.


DBMS consists of a collection of interrelated data that is called a database and a collection of programs to manage and access the data. An RDBMS is a collection of tables, each of which is assigned a unique name. Each table consists of a set of fields and stores a large set of records. A data warehouse is a repository of information collected from multiple sources, stored under a unified schema that resides at a single site. There have been a lot of developments in the field of database technology.

These developments include handling of spatial data such as maps; engineering design data such as design of buildings, components and circuits; multimedia data such as text, image, video and audio data; time related data such as historical records or stock exchange data and the World Wide Web data. Han & Kamber (2001) had described each of these advanced databases: 

1. Object Oriented Databases: In object oriented databases each entity is considered as an object. These objects can be customers, suppliers, employees or items. Objects that share a common set of properties can be grouped into a class that represents properties common to a class.

2. Object Relational Databases: In object relational data model much is the same as the basic relational data model but for the fact that object relational databases also handles complex data types and complex object structures.

3. Spatial Databases: These databases contain geographic databases, clip design databases, medical and satellite image databases. These data are represented in raster format, consisting of n-dimensional bit maps or pixel maps as well as vector format, consisting of basic geometric shapes such as points, lines and polygon etc.

4. Time Series & Temporal Database: These databases contain time-related data. A temporal database usually stores relational data that include time related attributes. A time series database stores sequences of values that change with time.

5. Text & Multimedia Databases: Text databases contain word description for objects (these could be long sentences or paragraphs). Multimedia databases store images, audio and video data. These databases are used in applications such as picture content-based retrieval, voice mail systems, video-on-demand systems & World Wide Web etc.

6. Heterogeneous Databases: Objects in one component database may differ greatly from objects in other component databases, making it difficult to assimilate their semantics into the overall heterogeneous database. There are special methods for analysis of such databases.

7. World Wide Web Databases: World Wide Web has data objects linked together to facilitate interactive access. Users seeking information of interest traverse from one object via links to another.


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