In DBMS locking, which lock mode prevents any other transaction from accessing an item (neither read nor write) while the lock is held?

Introduction / Context:
To preserve consistency, DBMSs use lock modes to control concurrent access. This question asks for the lock that blocks all other access (reads and writes) while held.

Given Data / Assumptions:

• Multiple transactions may attempt to read or modify the same item.
• We want a lock that denies all concurrent access by others.

Concept / Approach:
An exclusive (X) lock grants a transaction the sole right to read and modify the item and prevents other transactions from acquiring shared or exclusive locks on the same item until it is released.

Step-by-Step Solution:

Verification / Alternative check:
Lock matrix check: X with S = conflict, X with X = conflict; the item is fully isolated.

Why Other Options Are Wrong:

• Implicit/Explicit: describe how a lock is acquired (automatic vs. requested), not its blocking behavior.
• Shared lock: allows other shared locks and thus allows reads by others.

Common Pitfalls:
Assuming “exclusive” only blocks writers; in standard compatibility models, it blocks both readers and writers.

Final Answer:
Exclusive lock