As you see, the “Create User” use case from the “Requirements” package is covered by two design classes, and these classes are accordingly specified by this particular use case.
Therefore, the traceability properties such as Realizing Class and Realizing Element represent both design classes as realizing elements of this use case. Accordingly the traceability properties such as Specifying Use Case of each design class represent the “Create User” use case as a more specific element.
Note that the same related element can be represented through different traceability properties.