I'm trying to sketch out an ERD for booking hotel rooms. I had the "Reservation" as its own entity, so a User makes a reservation, and a reservation is for a room. But I guess it could also be an identifying relationship between the user and the room, as it joins them both. A user reserves a room. The reservation table would have a user_id and room_id. I would think other entities should be related to the reservation though, such as payment, rate of cost. Any input would help, I'm quite new to these. Thanks!
An identifying relationship is the relationship between a weak entity and its parent entity. A weak entity is an entity that can't be identified by its own attributes and has another entity's key as part of its own.
Does this apply to your situation? Is a User partially identified by the Room they reserve, or a Room by the User who reserved it? I would think not.
The other possibility is to make Reservation a regular relationship. Can a Reservation be identified by some combination of the entities it's related to? I don't think so. I imagine any Reservation could be repeated at a later date, but dates are usually seen as value sets, not entity sets.
Reservation should probably be an entity set.