I'm trying to design a schema for a board where quotes are posted. My primary models here are Quote, Line and Person. Here is a run down of the relationships:

Quote
belongs to many people
has many lines
has many people

Line
belongs to many people
belongs to one quote
has many people

Person
belongs to many lines
has many lines
has many quotes

I've rearranged these in so many ways, but I always run into trouble when I start thinking about foreign keys. I'm almost there if I just use quotes as a join table for people and lines, but a line can logically only have one quote! I think that I can just ignore this and be ok, but I'd really prefer to keep it as correct as possible. Any ideas?