You can select all rows in a transaction table that have one or more columns whose value matches (or doesn't match) values in dimension tables.
In the following picture, the selection criterion IsChildOf(Product, '[DIM_PRODUCT].[Credit Products]') AND IsChildOf(Channel, '[DIM_CHANNEL].[ATM]') selects six rows in the transaction table:
Notice that the IsChildOf property allows you to select from any point in a dimension hierarchy tree, and all children of that hierarchy are selected.