It is now presumed that the Student entity type has the functional dependency SID? This paper outlines the application of normalization principles to ERD development during the conceptual modeling phase. Codd, E. The second normal form deals with the situation when the entity identifier contains two or more attributes, and the non-key attribute depends on part of the entity identifier.
Another important consideration is to distinguish when one attribute alone is the entity identifier versus a composite entity identifier.
These guidelines can be stated as follows: There should be only one dependency in each entity type where the determinant is the entity identifier.
A composite entity identifier is an entity identifier with more than one attribute. This transformation can be useful to record a finer level of detail about an entity.