In case of "Prepare Itinerary", should I break it into several small sequence diagrams or cover everything in one big sequence diagram? There are 3 or 4 interactions with online customers in that use case and I really don't know how I can put them all in one sequence diagram. But if I break it into small pieces, then some of them(like System returns search result back to customer) will be too simple to have its own sequence diagram. Any suggestions? Thanks a lot.