For part 2 of the project, are we allowed to add/change the PK or are we just supposed to follow what was given in the ERD provided?

When considering the ERD provided, it is really difficult to understand the path of the arrow. Can you clearly give the path? As an example HiredVehicle - Invoice relationship, it is really difficult to understand the path of the arrow. I think this would be the answer for many students questions regarding ERD. Thanks.

Hi, I think you can easily infer the direction of the arrow based on the text. For Invoice it is Invoice --- generated for ---> HiredVehicle It is mentioned in this narration "Only after the vehicle is returned an invoice is generated for the vehicle hired" in the case study part. So I think if you get a bit confused by the direction of the arrow you can just read over the narration again. Or maybe you can also use common logic to infer the direction? For example I think HiredVehicle --- generated for ---> Invoice sounds a little bit weird. Because usually it is invoice which is generated for an order. Not the other way (generating order for an invoice). Hope this helps.