Complex sentence: The previous example only illustrates the definition of candidate key and not how these are in practice determiy the candidate keys it is important to determine "all" superkeys, which is especially difficult if the relation represents a set of relationships rather than a set of entities.
Split into simpler sentences: The previous example only illustrates the definition of candidate key and not how these are in practice determined. In order to determine correctly the candidate keys it is important to determine "all" superkeys, which is especially difficult if the relation represents a set of relationships rather than a set of entities.