FDs in Relationships:
Enrols Relationship: None as it is many to many
Teaches Relationship: Course code → Instructor
Instructor → Course code
The next question is: How do we recognize the functional dependence in a database model?
Functional dependencies occur from the nature of the actual world that the database models. Often A and B are facts about an entity where A may be some identifier for the entity and B some characteristic. Functional dependencies cannot be automatically determined by studying one or more cases of a database. They can be determined only by a careful study of the actual world and a clear understanding of what every attribute means.
There are no thumb rules for determining FDs.
Functional dependence is an vital concept and a large body of formal theory has been developed about it.