Question

Which of the following is called a database instance?

• A. Overall design of the database
• B. The snapshot of the database at any given time
• C. Data about the data
• D. Restriction on the type of data inserted

Answer 1

The Correct Option is B

In the context of databases, the term "database instance" refers specifically to the snapshot of the database at any given time. A database instance represents the data and its state in the database at a particular moment. This is dynamic and can change as the database is accessed and modified. 

Here is an explanation of why each option is associated with or not considered a database instance:

• Overall design of the database: This is related to the database schema, which defines the structure or design, and not the instance itself.
• Data about the data: This describes metadata, which provides information about data but not the data instance.
• Restriction on the type of data inserted: These are constraints that ensure data integrity but do not define the instance of the database.

Thus, the correct option is: The snapshot of the database at any given time.

Answer 2

(1) Overall design of the database: This refers to the database schema, not an instance. The schema is the blueprint that defines the structure of the database.

(2) The snapshot of the database at any given time: This is the correct definition of a database instance. It represents the actual data contained in the database at a specific moment in time, including all current records and their values.

(3) Data about the data: This describes metadata, which is information about the structure and properties of the data, not the instance itself.

(4) Restriction on the type of data inserted: This refers to data constraints or validation rules, which are part of the database schema definition.

Therefore, the correct answer is (2) The snapshot of the database at any given time, as this is what constitutes a database instance.