Concurrency basics: When two transactions are processed at the same time against the database, are they called concurrent transactions?

Introduction / Context:
Concurrency allows better throughput and resource utilization by overlapping transaction execution. The question asks for a basic definition: transactions executing during overlapping time intervals are concurrent.

Given Data / Assumptions:

• Two or more transactions overlap in time (start/end times intersect).
• They may or may not touch the same rows or tables.
• Database uses a concurrency control method to preserve correctness.

Concept / Approach:
Transactions are concurrent if their operations interleave. Even if they touch different data items, they are still concurrent. Concurrency control mechanisms (locks, MVCC, OCC) ensure correctness properties such as serializability or snapshot isolation.

Step-by-Step Solution:

Verification / Alternative check:
Schedulers interleave reads/writes from concurrent transactions into a single schedule; serial schedules have no interleaving.

Why Other Options Are Wrong:

• Requiring same table access is unnecessary; concurrency is about time, not object overlap.
• Isolation level differences are irrelevant to whether execution is concurrent.

Common Pitfalls:
Conflating contention (which needs same data) with concurrency (which needs just overlap). You can be concurrent without contention.

Final Answer:
Correct