Based solely and entirely on the requirements given, disregarding all possible real-world complications (such as what happens when an owner moves their car service from one garage to another):
I would leave out company. There’s only the one ever mentioned, and no indication that we are recording data for multiple companies.
The relationship between car owner and garage is through the car. There is no direct relationship between car owner and garage. (Given multiple garages, ensuring a given multiple-car owner appears once in the system is going to be tricky to enforce.)
The relationship between car and garage should perhaps be “registered at”. A strict reading implies that the car gets associated with the garage upon owner contact, not upon bringing in for service.
You need entity ServicePlanType [SPT]. Most SPTs are pre-defined, and multiple cars would use a given SPT (60,000 mile tuneup). Additional SPTs would be added if, when, and as required. An argument could be made for “standard” vs. “ad hoc” subtyping, but I think they’d be so similar (based on Operations) that this isn’t called for. Then:
- Service plan relates to one car, and to one service plan type
- Service plan relates to one service plan type
- Service plan type relates to zero or more service plans (list of standard plans)
- Service plan type relates to one or more operations (all operations must be defined)
Operation may relate to zero or more service plan types. Given the need for ad hoc service plans, there may be a need for operations that do not initially belong to any given set service plan. (That or they get added as needed, which may be acceptable. My sister’s gerbil got escaped once on the way home from school, and they had to disassemble part of the car to get it out. No charge, maybe they didn’t have “extract gerbil” it in their database.) (I am so not making that up.)
I would not relate sevice plan type or operation with garage. Presumably if one garage of the company can do it, they should all be able to do it, even the ad hoc ones.
You do not need to relate service plan with garage, as the car the service plan is for is related with garage. With that said, it might be good to do so when it comes time for physical implementation. Also, if a car is later brought into a second garage the car-to-garage relationship changes, and without the service plan to garage relationship, you lose track of who did the earlier work. Properly, I’d think you’d want to model owenr to car to service plan to garage, but they specifically spelled out “car to garage”. Raise these questions, see what the business owner says.
