Figure 1

The Relational Scheme of the database Single-edged arrows indicate a "one-to-one" relation, whereas double-edged arrows indicate "one-to-many" relation. When there are double-edged arrows in both ends of a connection (for instance the Receptor subfamily – G protein type, interaction), this is an indication of relation of the type "many-to-many", i.e. a particular G protein may couple to receptors of different subfamilies, whereas a single receptor may couple to G proteins of different types.