A database
system provides a data-definition language to specify the database schema and a
data-manipulation language to express database queries and updates. In
practice, the data-definition and data-manipulation languages are not two
separate languages; instead they simply form parts of a single database
language, such as the widely used SQL (Structured Query Language).
a) Data-Manipulation Language
A
data-manipulation language (DML) is a language that enables users to access or
manipulate data as organized by the appropriate data model. The types of access
are:
·
Retrieval of information stored in the database
·
Insertion of new information into the database
·
Deletion of information from the database
·
Modification of information stored in the
database
b) Data-Definition Language
We specify a
database schema by a set of definitions expressed by a special language called
a data-definition language (DDL). The DDL is also used to specify additional
properties of the data. We specify the storage structure and access methods
used by the database system by a set of statements in a special type of DDL
called a data storage and definition language. These statements define the
implementation details of the database schemas, which are usually hidden from
the users.
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