3. What is DBMS?
DBMS (Database Management System) is a system that is used to store
and manage data.
A DBMS is a set of programs that is used to store and manipulation data.
Manipulation of data includes the following:
Adding new data
Deleting unwanted data
Changing existing data
For example adding details of new student, deleting the details of
student who have completed course and modifying the fee paid by the student.
4. It provides various functions like:
Data security
Data integrity
Data sharing
Data concurrence
Data independence
Data recovery
5. RDBMS(Relational Database Management System)
RDBMS stands for Relational Database Management System. RDBMS data
is structured in database tables, fields and records.
Each RDBMS table consists of database table rows.
Each database table row consists of one or more database table fields.
RDBMS store the data into collection of tables, which might be related by
common fields (database table columns).
RDBMS also provide relational operators tomanipulate the data stored
into the database tables.
6. Most RDBMS use SQL as database query language.
The relation is the only data structure used in the relational data model
to represent both entities and relationships between them.
Rows of the relation are referred to as tuples of the relation and
columns are its attributes.
Each attribute of the column are drawn from the set of values known
as domain. The domain of an attribute contains the set of values that
the attribute may assume.
7.
8. Tuple /Row
A single row in the table is called as tuple. Each row represents the data
of a single entity.
Attribute/Column
A column stores an attribute of the entity. For example, if details of
students are stored then student name is an attribute; course is another attribute
and so on.
Column Name
Each column in the table is given a name. This name is used to refer to
value in the column.
9. Table Name
Each table is given a name. This is used torefer tothe table. The name
depicts the content of the table. The following are two other terms, primary key
and foreign key, that are very important in relational model.
Relational Algebra
A set of operators used toperform operations on tables is called as
relational algebra. Operators in relational algebra take one or more tables as
parameters and produce one table as the result.
The following are operators in relational algebra:
Union
Intersect
Difference or minus
Project
Select
Join
10. Union
This takes two tables and returns all rows that are belonging to
either first or second table (or both).
Intersect
This takes two tables and returns all rows that are belonging to
first and second table.
Difference or Minus
This takes two tables and returns all rows that exist in the first
table and not in the second table.
11. Project
Takes a single table and returns the vertical subset of the table.
Select
Takes a single table and returns a horizontal subset of the table.
That means it returns only those rows that satisfy the condition.
Join
Rows of two table are combined based on the given column(s)
values. The tables being joined must have a common column.
12. SQL(Structured Query Language)
Almost all relational database management systems use
SQL(Structured Query Language) for data manipulation and retrieval.
SQL is the standard language for relational database systems.
SQL is a non-procedural language, where you need to concentrate
on what you want, not on how you get it.
Put it in other way, you need not be concerned with procedural
details.
13. SQL Commands are divided into four categories, depending upon what
they do.
DDL (Data Definition Language)
commands are used to define the data. For example, CREATE TABLE.
DML (Data Manipulation Language)
commands such as, INSERT and DELETE are used to manipulate data.
DCL (Data Control Language)
commands are used to control access to data. For example, GRANT.
Query (Retrieving data)
It is used to retrieve data using SELECT. DML and Query are also
collectively called as DML. And DDL and DCL are called as DDL.
14. Advantages of RDBMS
A "relational database" is a database structured on the "relational" model.
Data are stored and presented in a tabular format, organized in rows and
columns with one record per row.
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