dia: in Chen's Notation, what are dot-bordered atts and what are multivalue atts for?

Question

I'm looking at , and I feel like I know what's going on until I see "PlayersIn" and "Foliage". Foliage is a double-line-bordered attribute because it is multivalued. What does that mean? How does it look in an actual database query? I don't know what the "PlayersIn" dotted-line bordering indicates. Can you please explain what it indicates, and when it is useful? What does it mean, what does a query look like, why is it important, etc.?