Summary: 1. e 1 > e 2 : If e 1 occurs, then e 2 must also occur. There is no
2. e 1 < e 2 : If e 1 and e 2 both occur, then e1 must precede e2.
Examples of execution dependencies defined in the
1. Commit Dependency : Transaction A is commit
dependent on transaction B, iff if both transactions
commit, then A commits before B commits. Let the
relevant significant events be denoted as cm A and cm B .
This can be expressed as cm A < cm B .
2. Abort Dependency : Transaction A is abortdependent
on transaction B, iff if B aborts, then A must also abort.
Let the significant events here be ab A and ab B , so this
can be written ab B > ab A .
The relationships between significant events of a task
can be represented by a task state transition diagram which
is an abstract representation of the actual task that hides
irrelevant details of its sequential computations. Execution
of the event causes a transition of the task to another state.
Figure 3 shows an example task state transition diagram