I find my self increasingly doing this order : Order(...) purcahse : Purchase(...) from order.items Where ... is for possible field constraints; so I figured some nice sugar for this would be purchase : Purchase(...) from Order(...).items So Order is a standard Pattern with standard field constraints, the difference it it has . operator at the end with the name of a field, or even possibly a method, which is what the 'from' uses as its data source. Mark