My comment
Based on the information provided (and including your
later remark that this is just a hypothetical conceptual model to help
illustrate a concept), Option A shows the right model.
Additional relationships as of your options B and C are redundant since they do not add any semantics to the model that are not already expressed in Option A. Practical test: If you generate foreign keys, the model as of Option A will look as shown at http://www.silverrun.com/common/ternary-example-red.gif (using the notation "Information Engineering +").
The foreign keys in the table Diploma still allow a direct navigation to the table University and the table Degree (and vice versa).
Additional relationships as of your options B and C are redundant since they do not add any semantics to the model that are not already expressed in Option A. Practical test: If you generate foreign keys, the model as of Option A will look as shown at http://www.silverrun.com/common/ternary-example-red.gif (using the notation "Information Engineering +").
Click on image to enlarge it
The foreign keys in the table Diploma still allow a direct navigation to the table University and the table Degree (and vice versa).
