Download Lecture # 10 - WordPress.com

Lecture # 10
Introduction To Database Systems
Content

Purpose of Database Systems

View of Data

Data Models

Data Definition Language

Data Manipulation Language
Database ?
Database:
A database is simply an organized collection of related
data, typically stored on disk, and accessible by possibly many
concurrent users.
Databases are generally separated into application areas. For
example, one database may contain Human Resource (employee
and payroll) data; another may contain sales data; another may
contain accounting data; and so on. Databases are managed by a
DBMS.
An Example
University Database:
Data about students, faculty, courses, research laboratories,
course registration/enrollment etc. Reflects the state of affairs of
the academic aspects of the university.
o
oPurpose: To
keep an accurate track of the academic activities of
the university.
Database Management System (DBMS)

A Database Management System (DBMS) is a set of programs
that manages any number of databases. A DBMS is responsible
for:

accessing data
inserting, updating, and deleting data
security
integrity



Database Management System (DBMS)
A general purpose software system enabling:
1.
2.
3.
4.
5.
Creation of large disk-resident databases.
Posing of data retrieval queries in a standard manner.
Retrieval of query results efficiently.
Concurrent use of the system by a large number of users
in a consistent manner.
Guaranteed availability of data irrespective of system
failures.
View of Data

In a database management system, a view is a way of
portraying information in the database.

This can be done by arranging the data items in a specific
order, by highlighting certain items, or by showing only certain
items.

For any database, there are a number of possible views that
may be specified. Databases with many items tend to have
more possible views than databases with few items.
Data Model

Collection of conceptual tools to describe the database at a
certain level of abstraction.

Conceptual Data Model a high level description useful for
requirements understanding.

Representational Data Model describing the logical
representation of data without giving details of physical
representation.

Physical Data Model description giving details about record
formats, file structures etc.
Data Definition Language- DDL

Data definition Language (DDL) which is used to create,
rename, alter, modify, drop, replace, and delete tables, Indexes,
Views, and macros; show data; comment on database objects;
and establish a default database.

DDL is abbreviation of Data Definition Language. It is used
to create and modify the structure of database objects in
database.
Data Definition Language- DDL
DDL provides statements for the definition and description of entities.
It enable you to perform the following operations:
1.
2.
CREATE Define a new database, user, table, trigger, index, macro,
view, depending on the object of the CREATE statement.
DROP Remove a table, trigger, index, macro, view definition,
depending on the object of the DROP statement
Other data definitions allow you to perform the following function:

ALTER Change a table, trigger or protection definition

RENAME table triggers views and macros

REPLACE macros, triggers or views

DELETE database or users
Data Definition Language- DDL
Data Definition Language (DDL) statements are used to
define the database structure or schema. Some examples:






CREATE - to create objects in the database
ALTER - alters the structure of the database
DROP - delete objects from the database
TRUNCATE - remove all records from a table, including all
spaces allocated for the records are removed
COMMENT - add comments to the data dictionary
RENAME - rename an object
Data Manipulation Language-DML

Data manipulation Language (DML) which is used to add,
delete, and revise data in existing tables or views.

DML is abbreviation of Data Manipulation Language.
It is used to retrieve, store, modify, delete, insert and
update data in database.
Data Manipulation Language-DML
DML supports statements for manipulating and processing
database values. It enable you to perform following operations:

BEGIN and END which is a user_defined transaction in
Teradata mode.

COMMENT : which is a transaction in ANSI mode.

INSERT : insert new rows into a table

UPDATE : modifies data in one or more rows of a table.

DELETE : removes a row from a table.
Data Manipulation Language-DML
Data Manipulation Language (DML) statements are used for
managing data within schema objects. Some examples:
 SELECT - retrieve data from the a database
 INSERT - insert data into a table
 UPDATE - updates existing data within a table
 DELETE - deletes all records from a table, the space for the
records remain
 MERGE - UPSERT operation (insert or update)
 CALL - call a PL/SQL or Java subprogram
 EXPLAIN PLAN - explain access path to data
 LOCK TABLE - control concurrency
Data Control Language-DCL

Data Control Language (DCL) which is used to control
database security; establish privileges and revoke privileges.

DCL is abbreviation of Data Control Language. It is used
to create roles, permissions, and referential integrity as well it
is used to control access to database by securing it.
Data Control Language-DCL
Data Control Language (DCL) statements. Some examples:
1.
2.
GRANT - gives user's access privileges to database
REVOKE - withdraw access privileges given with the
GRANT command