Test your understanding of the concepts covered in this section.
What is a major disadvantage of File Systems compared to DBMS?
- A) Higher cost
- B) Data redundancy and inconsistency
- C) Complex structure
- D) Need for specialized hardware
Correct Answer: B) Data redundancy and inconsistency
Explanation: File systems store the same data across multiple files (redundancy), and updates in one file may not reflect in others (inconsistency). A DBMS centralizes data to solve both.
In the 3-level abstraction, which level describes “how” data is stored?
- A) View Level
- B) Physical Level
- C) Logical Level
- D) Conceptual Level
Correct Answer: B) Physical Level
Explanation: The Physical (Internal) Level describes how data is actually stored on disk — file organizations, indexes, compression. The Logical Level describes what data is stored. The View Level describes what users see.
What does Logical Data Independence provide?
- A) Ability to change storage hardware without affecting logical schema
- B) Ability to change logical schema without affecting user views
- C) Ability to delete data without permission
- D) None of the above
Correct Answer: B) Ability to change logical schema without affecting user views
Explanation: Logical data independence means you can modify the conceptual schema (add columns, split tables) while keeping external views unchanged. Physical data independence (option A) is the ability to change storage without affecting the logical schema.
A “Schema” in DBMS is equivalent to:
- A) Actual data inside tables
- B) The overall blueprint or design of the database
- C) The user interface
- D) The database server brand
Correct Answer: B) The overall blueprint or design of the database
Explanation: The schema is the structural definition — table names, column types, constraints, and relationships. The actual data (instance) is what populates that structure.
Which ACID property ensures that a transaction is “all or nothing”?
- A) Atomicity
- B) Consistency
- C) Isolation
- D) Durability
Correct Answer: A) Atomicity
Explanation: Atomicity guarantees that either all operations in a transaction complete successfully, or none are applied. A bank transfer either debits and credits both accounts, or neither.
Which of the following is an example of a DBMS but NOT an RDBMS?
- A) PostgreSQL
- B) MySQL
- C) MongoDB
- D) Oracle
Correct Answer: C) MongoDB
Explanation: MongoDB is a document-based NoSQL DBMS. It stores data in JSON-like documents without enforcing relational constraints. PostgreSQL, MySQL, and Oracle are all RDBMS.
What is the main purpose of a CHECK constraint?
- A) To verify user login credentials
- B) To ensure a column value satisfies a specific condition
- C) To check if a table exists in the database
- D) To validate foreign key references
Correct Answer: B) To ensure a column value satisfies a specific condition
Explanation: CHECK constraints enforce domain integrity by validating that values meet a boolean condition. Example: CHECK (Age > 0 AND Age < 150) ensures valid ages.
What is Metadata?
- A) Large data files stored in binary format
- B) Data about data that describes structure and constraints
- C) Compressed database backups
- D) Encrypted user passwords
Correct Answer: B) Data about data
Explanation: Metadata describes the database structure — table names, column types, indexes, constraints. It’s stored in the data dictionary (system catalog) and queried via INFORMATION_SCHEMA.
Quick Revision Checklist
- Differentiate between Schema and Instance
- Explain why 3-tier architecture provides data independence
- List the 4 ACID properties and their meanings
- List 3 problems of File Systems
- Understand DBMS vs RDBMS distinction
- Name the 3 levels of ANSI-SPARC architecture
- Differentiate between physical and logical data independence
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