In SQL, what is meant by the term Data Definition Language (DDL) and what is its main purpose?

Introduction / Context:
Structured Query Language is divided into categories based on what type of operations statements perform. One important category is Data Definition Language, often abbreviated as DDL. Understanding what DDL does is fundamental for database design and administration. This question asks you to identify the best description of DDL in SQL.

Given Data / Assumptions:

• SQL statements can create, modify, or delete database objects.
• Some statements are used to query data, while others change structures or control transactions.
• The options mention structure management, querying, user interface design, backup, and transaction control.
• We assume familiarity with common SQL commands such as CREATE, ALTER, DROP, and SELECT.

Concept / Approach:
Data Definition Language refers to the part of SQL that defines and manages the structure of database objects. Typical DDL commands include CREATE TABLE, ALTER TABLE, DROP TABLE, CREATE INDEX, and CREATE VIEW. These commands change the schema, which is the blueprint of the database. They are different from Data Manipulation Language statements such as INSERT, UPDATE, and DELETE, which operate on the data stored in existing structures.

Step-by-Step Solution:
Step 1: Identify which SQL commands are commonly considered DDL: CREATE, ALTER, DROP, TRUNCATE, and similar schema changing statements. Step 2: Recognize that these commands define new objects, modify existing ones, or remove them from the database. Step 3: Compare this role with the options. Option a states that DDL defines and manages the structure of database objects such as tables, indexes, and views, which matches the standard definition. Step 4: Observe that querying data with SELECT is part of Data Query Language and manipulating data rows is part of Data Manipulation Language. Step 5: Confirm that user interface design, backup, and transaction control are not the core purpose of DDL.

Verification / Alternative check:
Consider the process of building a new application. The first step is usually to define the tables, columns, data types, and relationships. All of this is done with DDL commands like CREATE TABLE and ALTER TABLE. Only after the structure is ready do you start inserting and querying data, which uses other categories of SQL. This clearly shows that DDL is about structure.

Why Other Options Are Wrong:
A subset of SQL used only for querying data without changing any structures is closer to Data Query Language and does not capture the role of DDL. A graphical tool for designing user interfaces is not part of SQL itself. A backup mechanism that automatically stores copies of data on external drives refers to backup utilities or maintenance plans, not DDL. A feature used exclusively for transaction control and rollback operations corresponds to Transaction Control Language commands such as COMMIT and ROLLBACK, not DDL.

Common Pitfalls:
Students sometimes group all SQL under one label and forget the subcategories. While knowing the exact labels is mainly important for exams, the underlying distinction is very practical: DDL changes the structure, DML changes the data, DCL controls permissions, and TCL deals with transactions. Keeping these categories clear in your mind will help with both design and troubleshooting.

Final Answer:
Data Definition Language is a subset of SQL used to define and manage the structure of database objects such as tables, indexes, and views.