Which of the following statements are wrong? I. The two-phase locking protocol…
2009
Which of the following statements are wrong? I. The two-phase locking protocol suffers from deadlock. II. Compared with lock-based protocols that wait for conflicting locks, the basic timestamp-ordering protocol may cause more transaction aborts. III. A black hole in a DFD is a data store with only inbound flows. IV. Multivalued dependency among attributes is checked at the 3NF level. V. An entity-relationship diagram is a tool to represent an event model.
Answer: C. III, IV, V — ConceptConcurrency-control protocols differ in how they handle conflicts: two-phase locking can wait and deadlock, whereas timestamp ordering preserves its…
- A.
I, II, III
- B.
II, III, IV
- C.
III, IV, V
- D.
II, IV, V
Attempted by 14 students.
Show answer & explanation
Correct answer: C
Concept
Concurrency-control protocols differ in how they handle conflicts: two-phase locking can wait and deadlock, whereas timestamp ordering preserves its timestamp order by rolling back conflicting transactions rather than waiting.
In database design, multivalued dependencies are handled by Fourth Normal Form (4NF). In systems modelling, a DFD black hole is a process with input but no output, while an ER diagram represents static data structure—entities, attributes, and relationships—not events.
Application
Statement I: Two-phase locking guarantees conflict-serializable schedules but not deadlock-freedom, so deadlock can occur. The statement is true.
Statement II: Timestamp ordering resolves an order-violating conflict by aborting and restarting a transaction, which can produce more aborts than waiting-based locking. The statement is true.
Statement III: A DFD black hole is defined for a process that consumes input without producing output, not for a data store with only inbound flows. The statement is false.
Statement IV: Multivalued dependency is the defining concern of 4NF; 3NF addresses transitive functional dependency. The statement is false.
Statement V: An ER diagram models data entities and their relationships; an event model describes behavioural events. The statement is false.
Cross-check / contrast
I, II, III contains the two true concurrency statements and only one false statement.
II, III, IV still contains the true timestamp-ordering statement.
II, IV, V also contains the true timestamp-ordering statement.
III, IV, V contains all three false statements and excludes both true statements.
Therefore, the wrong statements are III, IV, and V.