With the way Qlikview works with selections, if you select 3, 4, 7, 10, sum(Value) will give 24. If you select 1, 2, 3, sum(Value) will give 6.
What kind of graph do you plan on doing with what dimensions? It may be possible to incorporate set analysis if they are dimensions involved. If this doesn't help, can you explain more or post a sample app demonstrating your problem?