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Database

Databases are designed to offer an organized mechanism for storing, managing and retrieving information. They do so through the use of tables. In simple terms we can say that in a Database the data is stored in Rows and Columns.

tablestructure

If you’re familiar with spreadsheets like Open Office Calc, you can easily understand the concept of Database Storage.

Database Tables

Database tables consist of columns and rows. Each column contains a different type of attribute and each row corresponds to a single record. For example, imagine that we are building a database table that contained student's details. We will probably set up columns named “Rollno”, “Name” , “Class” and "Address" .Then we simply start by adding rows those contains our data.

If we are building a table of student's information for our school that has 550 students, then this table will have 550 rows.

DBMS (Database Management System)

dbms

A Database Management System (DBMS) is a set of computer programs that controls the creation, maintenance, and the use of a database. A DBMS is a system software package that helps the use of integrated collection of data records and files known as databases. It allows different application programs to easily access the same database. A DBMS also provides the ability to logically present database information to the users.

Example of Commonly used DBMS

MYSQL,Oracle ,SQL SERVER 2000,MS Access

Advantages and disadvantages of DBMS

Advantages:

Reduced data redundancy (Duplication of data)

Reduced updating errors and increased consistency

Greater data integrity and independence from applications programs

Improved data security

Reduced data entry, storage, and retrieval costs

Disadvantages

Database systems are complex, difficult, and time-consuming to design

Damage to database affects virtually all applications programs

Initial training required for all programmers and users.

Relational database

Relational database was proposed by Edgar Codd around 1969. It has since become the dominant database model for commercial applications. Today, there are many commercial Relational Database Management System (RDBMS), such as Oracle, IBM DB2 and Microsoft SQL Server and many free and open-source RDBMS, such as MySQL, PostgreSQL are available.

A relational database organizes data in tables (or relations). A table is made up of rows and columns. A row is also called a record (or tuple). A column is also called a field (or attribute). A database table is similar to a spreadsheet. However, the relationships that can be created among the tables enable a relational database to efficiently store huge amount of data, and effectively retrieve selected data.

rdbms

Relational Model Concepts

Relation - table of values. Row is collection of related data values corresponding to real-world entity

Tuple – Row in a relation

Attribute - Column header or Column name of the Relation

Domain  - Set of atomic values permissible for a Column or an attribute. If the data type of a particular column in a relation is Number then the domain of that attribute is a number formed from the digit 0-9 e.g 123,398 etc.

Atomic - Value is indivisible, as far as relational model is concerned

Degree - Number of attributes in a relation

Cardinality -Number of rows/tuples in a relation

A language called SQL (Structured Query Language) was developed to work with relational databases.

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