What is the purpose of a Data-Manipulation Language and Data-Definition Language?

Data Definition Language

The Data Definition Language (DDL) is used to create and destroy databases and database objects. These commands will primarily be used by database administrators during the setup and removal phases of a database project. The DDL statements are also used to specify the integrity rules (constraints) in order to maintain the integrity of the database. The various integrity constraints are domain constraints, referential integrity, assertions and authorization. Like any other programming language, DDL also accepts input in the form of instructions (statements) and generates the description of schema as output. The output is placed in the data dictionary, which is a special type of table containing metadata. The storage structure and access methods used by the database system are specified by a set of definitions in a special type of DDL called a data storage and definition language. The purpose of DLL is hide implementation details of the database schemes from the users.

Data Manipulation Language

A DML is a language which enables users to access and manipulate data. Once the database schemas are defined and the initial data is loaded into the database, several operations such as retrieval, insertion, deletion, and modification can be applied to the database. The DBMS provides data manipulation language (DML) that enables users to retrieve and manipulate the data. The statement which is used to retrieve the information is called a query. The part of the DML used to retrieve the information is called a query language. A query language is a portion of a DML involving information retrieval only. The purpose of DML is to provide efficient human interaction with the system.