24 1 Hierarchies and Relationships
Figure 1.13 The human nuclear receptor gene superfamily. A common ancestor
evolved into the three gene families. Unlabeled arrows represent evolution over time.
Labeled arrows indicate translocation between families or subfamilies. See (Cooper
1999), Figure 4.28.ber of attributes for a set of entities is to be reduced to a small number of
attributes, usually two or three (Kohonen 1997). The attributes are then dis-
played using visual techniques that make the clusters easy for a person to
see. There are also many clustering techniques that combine some or all of
these techniques.Summary
- Classifications can be constructed top-down, bottom-up, or from the mid-
dle. - Classifications can be based on many principles: subclass (subset), in-
stance (member), or more complex relationships. - It is even possible for a classification to be based on several relationships
at the same time.