Exemplar basically means a typical example, or model, of a concept or role. However the meaning can be extended to mean he best example of a concept or role. For instance, someone might say that you are an exemplar student, which can mean that you are a great example, or model, of a student.
Answer: This is a way slave owners degraded slaves even more, making them feel less worth. Invoking the sense of only being property, it degrades them.
