What is RDBMS ? What is Relational Database design ?

• What is Relational Database design ?
  

        Relational database design provides guidelines to define tables, columns, and estahic data relationships between tables. A well-designed relational database should eliminate do is redundancy i.e. the same piece of data should not be stored in more than one place. This because duplicate data not only waste storage spaces but also easily lead to inconsistencies should also ensure data integrity and accuracy. 

• DATA REDUNDANCY :-
  

Data redundancy means finding the same data in more than one location within database tables. Redundancy in a relational schema is a non-optimal relational database design because of the following problems: 

1.  Insertion Anomalies 
   
   
2.  Deletion Anomalies 
   
   
3.  Update Anomalies 
   

•  Insertion Anomalies :-

               An insertion anomaly happens when the insertion of a data record is not possible unless we also add some additional unrelated data to the record.

• 
  
•  Deletion Anomalies :-
  

              A deletion anomaly happens when deletion of a data record results in losing some unrelated information that was stored as a part of the record that was deleted from a table .

• Update Anomalies :-

             An update anomaly occurs when updating data for an entity in one place may lead to inconsistency. with the existng redundant data in another place in the table.

• What is RDBMS ?

RDBMS (Relational database management system) is a type of database management system that is based on the relational model as introduced by Dr. E. F. Coda.

                  RDBMS is basically an information system that presents information as records (rows) COntaaned in a collection of tables (relations), where each table possessing a set of one or OP Columns (attributes). This means database tables are the primary data storage for every KDBMS and essentially they are collections of related data entries. 

         For example: The following table called "USERS" might store information aboul many s, and each entry in this table will represent one unique user. Even though all user entries in ' USER' table are unique they are related in the sense that they describe similar objects .

      RDBMS store the data into group of tables. which might or might not be relaled by common fields or columns. RDBMS also provide relational operators to insert / update / delete .

    In RDBMS. the term data dictionary can be defined as a table of tables. It contains a st of athe tabies exist in the database, as well as the structure of the tables and often. specta nformation about the datanuse Eselt. Data dictionaries do not contain any actual data r e datahase. oaly book-keeping intorination for managing it. Without a data dictioly towever. a database management system cannot access data from the database.                    Today the relational database is at the core of the information systems for orgmizations, both publac and private. fnformir, Sybase, SQL Server and Oracle ac 06 rTu RDBMS pruducts having workdwide acceptance.

• What is Key in Dbms ?

1. Super Key /Candidate Key 
   
   
2.  Primary Key 
   
   
3.  Altenate Key 
   
   
4.  Composite Key 
   
   
5.  Foreign Key 
   
   

• Super Key / Candidate Key :-

         It is such attribute of a table that can uniquely identify a row in a table . Generally they contain unique values and can never contain NULL values. There can be more than one super key or candidate key in a table. For example: In a STUDENT table, Roll No and Mobile No Can both serve to uniquely identify a student. 

• Primary Key :-  

       It is one of the candidate keys that are chosen to be the identifying key for the entire table. For example: Although there are two candidate keys in the STUDENT table, the college would obviously use Roll_No as the primary key of the table .

• Alternate Key :-

             This is the candidate key which is not chosen as the primary key of the table. They are aned so because although not the primary key, but they can still identify a row. For eample: As Roll_No and Mobile_No are two candidate keys in the STUDENT table. If Ko_No set as a primary key, then the other candidate key Mobile_No act as an altemate key 

• Composite Key :-

     Sometimes one key is not enough to uniquely identify a row. For example, in a single 5, Roll_No is enough to find a student, but in the entire college, merely searching by the Ot enough, because there could be 10 classes in the college and each one of them may acerntain roll no 5. To uniquely identify the student we have to say something like 4ss BCA-II, Roll No 5". So, two or more attributes are combined to create a unque of values. such as Class + Roll_No. Such combination of two or more attributes make a composite key .

• Foreign Key :-  

A foregin key is a relationship or link between two tables which ensures that the dbms stored in a database is consistent . The foregin key link is set up by matching columns in table to the primary key coloums in another table .

            So. foreign key is a field in a relational table that matches the primary kev column of another table. Such a copy of another related table's primary key is called Foreign kev,

Difference between DATA and INFORMATION ?

Data:- 

1. Data is raw fact and figures. For example: 32 is data.
2. Data is not significant to a business. 
3. Data does not help in decision making .
4. Observations and recordings are done to obtain data .
5. Input to any system may be treated as data .
6. Difficult to understand properly.
7. Data must be processed to understand. 
8. Data may not be in the order. 

Information:- 

1. Information is a processed form of data. For example: Age 32.
2. Information is significant to a business.
3. Information helps in decision making.
4. Analysis is done to obtain information.
5. Output system Information.
6. Easy to understand. 
7. Information is already in understandable form. it may be processed further to make it more understandable. 
8. Information should be in the order. 

INTRODUCTION TO DATABASE:-

                                                                 Data is a very important resource in the operation and management of an organization. So, it is very essential to organize the data in a meaningful manner, because an unorganized data has no meaning. With the increased demand of the data in the various organizations such as banks, universities, railways, airlines, companies etc., it becomes a necessity to store data in an organized manner so that it can be used again and again. So, we need a database to store the data in an organized form.

                                                 To understand the concept of database, let us consider an example of telephone directory in which names of people are arranged in an alphabetical order. So, it becomes easier to search any phone number corresponding to a particular name. If this ordering is not done in n organized manner then it is very difficult to scarch a phone number of a particular person, so this shows why database are needed.

DATABASE OPERATIONS:-

                                      To maintain huge databases, we need certain operations which help in maintaining the data in the database efficiently. The most commonly used operations performed on the databases are:- 

(a) Insertion: To add new data into the database. (For example: To add new phone number into the telephone directory.) 

(b) Selection: To view or retrieve the stored data. (For example: To view a telephone number of a particular person from the telephone directory.) 

(c) Updation: To modify or edit the existing data. (For example: Suppose the phone number of a particular person is changed, so we have to modify the telephone directory by replacing his old phone number with a new phone number.) 

(d) Deletion: To remove or delete the existing data from the database. (For example: Suppose an employee has left the organization, so his record should be deleted from the employee database of the organization.) 

(e) Sorting: To arrange the data in a desired order (ascending / descending). (For example: In employee database of an organization, records should be aranged in an alphabetical order for easy and fast retrieval.)

DATABASE APPLICATIONS:-

                                               The collection of data, usually referred to as the database, contains information relevant O an enterprise. Today, database systems are widely used to manage large bodies or information. Some of the important database applications are:-

• Banking: For customer information, aceounts, and loans. and banking trane . 
• Universities: and grades For student infomation, course registrations, results and grad . 
• Airlines: For rvations and schedule information. Airlines inals were situated among around the use databases in a geographically distributed manner-termina situated around the world  acressed the central database system through phone lines and networks. 
• Credit card transact For purchases on credit cards and generation  statements. 
•  Sales: For customer. product, and purchase information. 
•  Telecommunication: For keeping records of calls made, generating monthly monthly hi bil maintaini balances on prepaid calling cards, and storing inrormation about communication networks. the 
•  Manufacturing: For tracking production of items in factories, inventories of itemsi warehouses/stores. and orders for items. ms in
•  Human resources: For information about employees, salaries and payroll taxes etc. 

MANUAL DATABASE Vs. COMPUTERIZED DATABASE:-

Manual Database:-

1. Manual database is a record keeping systems in which human being manage the whole database without the support of computers. 
2. A manual database is like a filing cabinet , and is very slow .
3. In a manual database system, information must be typically found by hand rather than  electronically. Someone looking for information in a manual database may have to spend hours searching for a particular piece of data, which is a very time consuming job. 
4. Less reliable.
5. Manual database system has slow processing speed . It take a lot of time to perform various database operations like sorting , insertion , deltion and searching .
6. Manual datadase systems can be very complex and inaccurate .
7. More prone to data loss and data duplicity.
8. Difficult to modify or update anual database .

Computerized Database:- 

1. Computerized database is a database that can be managed or accessed by computers.
2. A computerized database is store in computer , and very fast organizing information .
3.  A computerized database will typically allow users to search the entire database for specific information in seconds.
4. More reliable than manual database system .
5. Computerized database system has very fast processing .
6. Computcrized database more accurate and easy to process .
7. Less prone to data loss and data duplicity .
8.  Computerizcd database can be eaily modificd .

APPROACHES TO DATA MANAGEMENT:-

                                                   With the advancements in computer technology, there was a nced to computeTIE he manual way of storing the data in database. Two approachcs uscd for data tIanapenCHl through computers are:-

1. File System Approach
2. Database Approach  

1. File System Approach :- 

                                            File system approach was an early attempt to computerize the manual filing system. t is basically a collection of application programs that performed services for the end users. ach program within a file based system defines and manages its own data. In this system, a large number of files are needed to perform various tasks. For example: In sales department of an enterprise, one user will be maintaining the details of how many sales personnel are there in the sales department and their grades, these details will be stored and maintained in a separate file. Another user will be maintaining the salesperson salary details working in the concern, the detailed salary report will be stored and maintained in a separate file. Although both of the users are interested in the data's of the salespersons they will be having their details in separate files and they need different programs to manipulate their files. This will lead to wastage of space and redundancy or replication of data's, which may lead to confusion, sharing of data among various users is not possible, data inconsistency may occur.

2. Database Approach:-

                                      In order to remove all the above limitations of the File system approach, a new approacn was required that must be more effective. So, the concept of database was introduced. This approach is known as database approach. A database is a computer based record record and maintains keeping system whose over all purpose is information. The database is a single, large repository of data, whicn can be used simultaneously by many departments and users. With the database instead of disconnected files with approach redundant data, all data items are integrated with minimum amount of duplication and maintained only at one location .

Characteristics of File System Approach:-

                                                            Some important characteristics of file system approach are: 

1. It is a group of files storing data of an organization .
2. Each file is independent from one another .
3. Each file is called a flat file . 
4.  Each file contained and processed information for one specific task, such as accounting or inventory.
5. Files are designed by using programs written in programming languages such as C++ .