8 1 Hierarchies and Relationships
constantly categorizing objects, experiences, and people. We do it effortlessly
and unconsciously. The very words we use to express ourselves represent
categories. It is only when a categorization is problematic that we notice that
we have been categorizing at all. Biology was the first discipline to engage
in systematic, large-scale classification because of the enormous complexity
of its domain.Figure 1.3 A BioML document showing some of the information about the human
insulin gene. Boxes were drawn around each XML element so that the hierarchi-
cal structure is more apparent. XML documents normally indicate the hierarchical
structure by successive indentation, as in this example.What makes XML powerful is the ability to organize data hierarchically.
XML elements are much more than just self-describing records; each element
can contain other elements, which can contain other elements, to arbitrary
depth. Figure 1.3 shows a small part of the genomic data for the insulin gene