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Database Languages:

The widely used SQL language is basically a combination of two database languages, 

DDL (Data Definition Language) and DML (Data Manipulation Language).

Data Definition Language (DDL):

It is used to specify the schemas in the database using a set of schemas. Consider the following example, that uses SQL language:

Create table Student(Student-id varchar2(10), Student-name char(50), Class integer(3));

After executing the above statement, along with the Student table, data dictionary (also known as data directory) is created.

Data Dictionary contains data about data-metadata. For any reading, updating, and modification purposes, the data dictionary is consulted.

By using a special type of DDL- data storage and definition language, storage structure and access methods used by the database system can be specified. These statements hide the implementation details of the database schemas from the users.

Data Manipulation Language (DML)

People synonymously use the term query language with DML, however, this is not technically correct. The query language is a portion of DML that is used for information retrieval purposes. DML is used for the following purposes:-

a. Information retrieval

b. Adding new information to the databases

c. Deletion of information from the databases

d. Modification of information stored in the databases.

DML can be further can be classified as follows:

1. Procedural DML or Low-Level DML

2. Non-Procedural DML or Declarative DML or High-Level DML

1. Procedural DML or Low-Level DML: Procedural DML requires the user to specify what data are required and how to access that data by providing a step-by-step procedure.

Example:  Relational algebra is a procedural query language.

2. Non-Procedural DML or Declarative DML or High-Level DML: Non-procedural requires a user to specify what data are required without specifying how to retrieve the required data. 

Example: SQL (Structured Query Language) is a non-procedural query language.

Storage Definition Language (SDL):

The storage definition language (SDL), is used to specify the internal schema. This component is removed from the current SQL version to keep it conceptual and external level only.

View Definition Language (VDL):

For the implementation of a true three-schema architecture, this language is required to specify user views and their mappings to the conceptual schema. This is generally implemented using DDL in most DBMS. In relational DBMS, this language is defined using SQL.