RDBMS system metadata: which statements about “system information” are generally true?

Introduction / Context:
Every relational database maintains metadata—definitions of tables, columns, indexes, constraints, privileges, and more. Understanding where and how this metadata is stored and accessed is essential for administration, introspection, and tooling.

Given Data / Assumptions:

• RDBMSs maintain catalogs or data dictionaries implemented as system tables or views.
• Users typically query these using SQL (e.g., INFORMATION_SCHEMA, system catalogs).
• Direct updates to metadata tables are usually restricted for integrity and safety.

Concept / Approach:
The metadata catalog describes schema objects and is exposed through read-only views. DBMS controls updates via DDL (CREATE/ALTER/DROP), not ad-hoc DML into catalog tables, to preserve system integrity.

Step-by-Step Solution:

Verification / Alternative check:
PostgreSQL exposes pg_catalog; SQL Server has sys.* views; MySQL has INFORMATION_SCHEMA; Oracle uses data dictionary views (e.g., DBA_TABLES).

Why Other Options Are Wrong:
Each individual statement (A, B, C) is true; therefore “All of the above” is the only fully correct choice.

Common Pitfalls:
Attempting to UPDATE system tables directly can corrupt metadata; always use DDL statements to modify schema.

Final Answer:
All of the above.