In database systems, the database schema (definition of tables, columns, and constraints) is primarily written using which type of SQL commands?

Introduction / Context:
Relational database systems use Structured Query Language to perform many types of operations. One important category of operations defines the structure of the database itself, including tables, columns, indexes, and constraints. This structural description is known as the database schema. Understanding which SQL category is used to define the schema is fundamental for database design and administration.

Given Data / Assumptions:

• We are discussing standard SQL categories such as DDL, DML, DCL, and TCL.
• The database schema includes CREATE TABLE, ALTER TABLE, and DROP TABLE operations.
• Application code in high level languages uses the database but does not define the schema directly.
• Data control and transaction control are related to security and consistency, not schema definition.

Concept / Approach:
Data Definition Language commands define and modify database structures. Typical DDL statements include CREATE, ALTER, and DROP. These commands create tables, views, indexes, and constraints that together form the schema. DML commands such as SELECT, INSERT, UPDATE, and DELETE manipulate data stored in these structures but do not define them. DCL commands manage permissions, and TCL commands manage transactions. Consequently, the correct answer must identify DDL as the category that is used to write the database schema.

Step-by-Step Solution:
Step 1 Recall the main SQL categories: DDL for structure, DML for data, DCL for access control, and TCL for transactions. Step 2 Note that schema definition involves creating tables, specifying columns, data types, and constraints. Step 3 Recognize that commands like CREATE TABLE and ALTER TABLE are DDL commands. Step 4 Select the option that names DDL as the language used to write the database schema.

Verification / Alternative check:
Database documentation consistently classifies commands that create or change database objects as DDL. For example, the CREATE TABLE statement is clearly labeled as a DDL operation. Tools that generate schema scripts commonly produce collections of DDL statements. In contrast, examples of DML focus on manipulating rows inside tables and do not define structural elements, which confirms the distinction.

Why Other Options Are Wrong:
High Level Language refers to programming languages such as Java, C plus plus, or Python, not an SQL category. Data Control Language manages privileges and roles, such as GRANT and REVOKE statements. Data Manipulation Language covers operations that insert, update, delete, or query data, not operations that define tables. Transaction Control Language covers commands like COMMIT and ROLLBACK, which manage transaction boundaries, not schema definition.

Common Pitfalls:
Students sometimes confuse DDL with DML because both use SQL syntax. Another common error is assuming that SELECT, which is very frequently used, is part of schema definition, when in fact it only retrieves data. Keeping the mapping clear between SQL categories and their purposes helps in both exams and real world database design work.

Final Answer:
The database schema is primarily written using DDL (Data Definition Language) commands.