Explanation

This question describes a transaction in distributed systems that can be built based on a number of subtransactions. The highest-level transaction can branch and generate "children" that are executed in parallel on different machines to gain performance or simplify programming.

Key concepts:

1. Nested Transactions: This is exactly what the question describes - a transaction that contains other transactions (subtransactions) that can execute in parallel. In nested transactions, the parent transaction can spawn child transactions that can commit or abort independently, with the parent transaction controlling the overall outcome.

2. ACID Properties:

   • A (Atomicity): All operations in a transaction succeed or all fail - not what's described here
   • C (Consistency): Database constraints are maintained - not relevant
   • I (Isolation): Transactions don't interfere with each other - this is a property, not a transaction type
   • D (Durability): Committed transactions persist - this is a property, not a transaction type

3. Distributed Transactions: The question specifically mentions distributed systems and parallel execution on different machines, which aligns with nested transaction models where subtransactions can execute on different nodes.

Why other options are incorrect:

• B) Isolamento: This is one of the ACID properties (Isolation), not a transaction type
• C) Transação isolada: This isn't a standard transaction type; isolation is a property
• D) Transação atômica: Atomicity refers to the "all-or-nothing" property, not hierarchical transaction structures
• E) Durabilidade: This is another ACID property (Durability), not a transaction type

Correct Answer: A) Transação aninhada (Nested Transaction)