Introduction to DBMS

Degree : Degree of relation is the number of attributes it contain

Cardinality: Cardinality of relation is the number of tuples it contain

Relation: Relational database is a collection of normalized relation with distinct relation names 

DATA :

Data usually refers to raw data, or unprocessed data. It is the basic  form of data, data that hasn’t been analyzed or processed in any manner. Facts could be in any format. Data can be a numeric, text, graphics, images etc…

Example: 1234,Joe,8015553211

Meta Data :

Data that describe the properties of other data is known as Meta data.

 

INFORMATION:

Data becomes information when it is processed, turning it into something meaningful.

Processed data that could be used to increase the knowledge of the user.

Example :

• Id No is 1234,
• Name is Joe,
• Contact No is 8015553211

Knowledge:The ability of person recalls or uses his information and experience is known as knowledge. Knowledge is of two types:

1.Facts based Knowledge.

2.Information based Knowledge.

DATA DICTIONARY :

A data dictionary is a file or a set of files that contains a database's  metadata. The data dictionary contains records about other objects in the database, such as data ownership, data relationships to other  objects, and other data. The data dictionary is a crucial component of any relational database.

DATABASE:

The collection of data is usually referred as database. The primary goal of DBMS is to provide an environment that is both convenient and efficient to store and retrieve data from the database

Ex: a bank, a hospital, a company etc…

 

DBMS:

A DBMS provides an efficient storage and Data Management Mechanism. There are many software tools which use these data bases to store and maintain the huge volume of data.

 

Operations of Data:

1.Store the data

2.Retrieve the data

3.Update/modify the data

4.delete/Remove.

5.Share the data among different uses

6.Ensuring the security of data.

7.Recover the data in case of failure.

8.Write application programs based on the data. 

Commercially available Database management systems in the market are dbase, Oracle, MySQL, SQL Servers and IBM DB2 etc.

Introduction to Oracle Tools : 

ORACLE  --->  Oak Ridge Automatic Computing Logical Engine

SQL -->Structured Query Language. It is a 4^th generation language.

Forms -->It is the default front-end tool for oracle.

PL/SQL -->Back end for oracle.

Front end -->It is medium through which users is interacting with server.

FILE :

• A file is a collection of records which have common properties.
• Each file has its own file reference which is unique.
• The file reference indicates the subject or contexts of the records.
• A record can be an image, text based or in electronic or physical format.

FILE SYSTEM :

• The file system is software which is used to manage the data that are stored in files.
• If we want to store data in files then different programs are to be written in order to store the data.

DBMS CONCEPTS:

1.Data Redundancy and Inconsistency:

        Data redundancy occurs when the same piece of data exists in multiple places, whereas data inconsistency is when the same data exists in different formats in multiple tables.

Example: If the address of employee present in two files say emp.mast emp.personal. So it leads to redundancy. In addition it may lead to data inconsistency. It implies various copies of the same data may no longer agree. For example The changed address is only reflected in emp.mast but not in emp.personal. Hence data inconsistency occurs.

2.Difficulty in Accessing Data:

        Suppose one of the managing Director asks his computer operator to give him a report of all employees who joined in a particular year. Since this request was not anticipated program, when the original file was designed there is no application program on hand to meet it The point here is that conventional file processing do not allow the needed data to be retrieved in a convenient and efficient manner.

A file management system manages the way of reading and writing data to the hard disk. It is also known as conventional file system. This system actually stores data in the isolated files which have their own physical location on the drive, and users manually go to these locations to access these files.

3.Data concurrency:

        Data concurrency is the ability to allow multiple users to affect multiple transaction within a database. Simply, data concurrency allows multiple users to access data all at the same time.

For ex: consider bank account ‘A’ with Rs 500. If two customers withdraws funds, say Rs.50 & Rs.100 from A/c ‘A’ at about the same time. The result of the concurrent execution may leave the data in an inconsistent state. In particular the A/c may contain Rs.450 or Rs 400 rather than Rs.350.

4.Security Problems:

        Not every user of the database system should be able to access all the data.

For ex: In an employer organization you don’t want to show the salary of manager a part from other details to other users. We can restrict this by Data Base Managing System.

5.Integrity Problem:

        The data values stored in the database must satisfy certain types of consistency constraints such as Integrity Constraint is used to ensure that the primary key cannot be null. A primary key is used to identify individual records in a table and if the primary key has a null value, then we can't identify those records.