Attached is an exercise from a book that I am having difficulties answering.
hireDate & carReg are the primary keys. So my question can anyone find any extra functional dependencies other than the ones I have identified below....Modifications also welcome:
fd1 carReg -> make, model, outletNo, outletLoc
fd2 custNo -> custName
fd3 outletNo -> outletLoc
fd4 model -> make (only if we assume a model name is unique to a make)
fd5 carReg, hireDate -> make, model, custNo, custName, outletNo, outletLoc
I'm not sure if the above are correct and I am sure there are more. Please can someone help me finally understand these damned FD's!
I am sure there are more FD's. For example given the relation, custName -> custNo. But if for arguments sake, another J Smith was added, this wouldn't hold. I know by definition functional dependencies must hold for all time...Therefore custName -> custNo is invalid even for the attached instance of the given relation...Am I correct?
Please let me know if anything needs more clarification...