Every room in a building is identified by a room No and has precisely one telephone. Each telephone has its own distinct telephone Extension No. There are two types of telephone, internal dialling...

Every room in a building is identified by a room No and has precisely one telephone. Each telephone has its own distinct telephone Extension No. There are two types of telephone, internal dialling only (type I), and external/internal dialling (type E). The rental charged depends only on the tariff. Type I telephones are charged on tariff T1, and type E on tariff T2. Information on rooms and telephones will be held in the table:

Making any further plausible assumptions necessary:

(a) draw a determinancy diagram for Office;

(b) write down the candidate identifier(s).