How is RIA services for relational data efficiency?

I have been researching RIA services with silverlight 4 and considering using it. Switching to silverlight from ASP gives me some concerns about the maturity of silverlight for data driven apps.

I was looking at relational data queries. Lets say I have a 'person' table and a 'cars' table. Multiple cars can be associated with a person. Now if I do queries with relational data I have to specify to include the additional tables to be returned to the client from the server. Shown here:

http://timheuer.com/blog/archive/2010/01/05/master-details-with-ria-services-and-includedresults.aspx

I am a little concerned with efficiency. If I do something like this, it appears I am potentially sending multiple rows from the car table for each person row (since its one to many). However, I may only want the name of the car and not other columns. A more complex example with a bunch of relational joins to other tables could get ugly. Is there any way to address this? I don't see much info on custom/complex types or how ria services handles database views.

Another thought of mine is if I have relational data that loops back on itself will that lock up a query. For example if person links to a car and car links to some other table and that table links back to person. It could seemingly loop forever?