Let us assume that the total number of votes in the system is V and the abort and commit quorums are Va and Vc, respectively.
To ensure serializability, no two transactions should be allowed to read or write a data item concurrently.
In case of replicated databases, a quorum-based replica control protocol can be used to ensure that no two copies of a data item are read or written by two transactions concurrently.
Additionally, it ensures that a read quorum contains at least one site with the newest version of the data item.
The second rule ensures that two write operations from two transactions cannot occur concurrently on the same data item.