In the case study, it mentions that tariff type and depot should be recorded when a vehicle is hired - am I correct in thinking that these are foreign keys in the Hire entity (which connects Vehicles and Clients) and hence we shouldn't write them into the Hire attributes on the diagram or in the data dictionary? I'm assuming you'd record the id code of depot and tariff type so they would be FKs in Hire. Also, is there no need to connect the Hire entity with the Depot and Tariff Type entities directly seeing as Hire is connected to Vehicle which is in turn connected to Depot and additionally Vehicle connects to Make which connects to the Tariff Type entity? The case study also mentions that the odometer reading of a car is recorded when the car is hired - should 'odometer reading' then be written as an attribute in Hire, seeing as it is not a PK of Vehicles? Is hire time and date a single-valued attribute of type 'date'? Are type (EV, hybrid, fuel) and make different? Are hirers and clients the exact same? I have a composite key made up of two foreign keys A and B - can I write the composite key in its entity as A{PK} B{PK} in my diagram? And I'm guessing this composite key should be in the data dictionary. How should subclasses be expressed in the attributes data dictionary? Should we list them under the Entities column as usual but in their attributes only mention the attributes unique to that subclass? I'm guessing I should given an indication in the dictionary that they are a subclass of another entity as well. Thank you very much in advance.