SCOP(e) concise classification string

This is a dot notation used to concisely describe a SCOP(e) class, fold, superfamily, and family. For example, a.39.1.1 references the 'Calbindin D9K' family, where 'a' represents the class, '39' represents the fold, '1' represents the superfamily, and the last '1' represents the family.