Parallel Activities handling

You can use a preceeding rule on activity D for this.  A preceeding rule must evaluate to true before the activity is allowed to execute.  The preceeding rule is only evaluated when a line rule coming into the activity executes.

Create two process level boolean variables (like BComplete and CComplete) and given them an initial value of false.  In a server code event at the end of activities B and C set the boolean flags to true.  In the preceeding rule of D check the condition to check that the two datafields are true.

Check out the K2 book for lots of information like this.

thanks for you answer

but what about the two instances that appear in the worklist of the user who is in the destination rule of  D when B and C are complete. just try the scenario i provided and see for your self.

If you have set the preceeding rule on D correctly so it can only be true if B & C have both completed, then you will get only one instance of D.

Thanks for your effort and time...problem is solved