Question

A precedence graph - also known as a serializability graph - captures all the potential conflicts between transactions in a schedule. Which of the following is true about a precedence graph?

a) There exists an node for all aborted transactions in S.
b) There exists an edge from Ti to Tj if an action of Ti precedes and conflicts with one of Tj's actions.
c) There exists a node for each transaction in S.
d) There exists a node for each committed transaction in S.
e) There exists an edge from Ti to Tj if an action of Ti succeeds and conflicts with one of Tj's actions.

Answer 1

The correct statement about a precedence graph is that there exists an edge from Ti to Tj if an action of Ti precedes and conflicts with one of Tj's actions. In precedence graphs, nodes represent transactions and edges indicate precedence due to conflicting operations. (option b)

Step-by-step explanation:

A precedence graph, also known as a serializability graph, is used in database systems to test if a schedule (the order in which transactions are executed) is serializable. Serializability is an important concept in the context of database concurrency control, ensuring that transactions execute in a way that leaves the database in the same state it would be if the transactions were executed serially.

The correct statement about a precedence graph is:

b) There exists an edge from Ti to Tj if an action of Ti precedes and conflicts with one of Tj's actions.

This means that if transaction Ti has an operation that conflicts with Tj's operation and Ti's operation precedes Tj's operation, then the graph contains a directed edge from the node representing Ti to the node representing Tj.

Moreover, in precedence graphs, there is typically a node for each transaction in the schedule, whether or not the transaction is committed, and edges represent the precedence relation due to conflicting operations.