Testing for conflict serializabilit

Testing for conflict serializability
Under the constrained write rule (that is, a transaction updates a data item based on its
old value, which is first read by the transaction), a precedence (or serialization) graph
can be produced to test for conflict serializability. For a schedule S, a precedence graph is
a directed graph G = (N, E) that consists of a set of nodes N and a set of directed edges E,
which is constructed as follows: