Set based operations in Biztalk rule server

I am trying to create a rule that will loop through a stucture and check a
rule against each loop. So basically \”for each child node of this node check a certain value\”. Also is it possible to maintain a variable whilst running the loop to keep a tally of another value? Like if you are totalling up a value that is on each node? Not sure if this is clear enough please ask if you need more info.

Many Thanks in advance