1.3 Hierarchical Organization 7
It is also used to show where an element ends. To include the left angle
bracket in ordinary text, write it as “<”. Writing a special character like
the left angle bracket as “<” is calledescaping. The ampersand character
(&) is also reserved by XML, and it must be written as “&”.
Figure 1.2 Data entry screen for themoleculeelement of the Chemical Markup
Language.
Summary
- XML is a format for representing data.
- An XML element is analogous to a record in a flat file.
- An XML attribute is analogous to a field of a record.
- An XML DTD is a schema that describes the structure of the elements of
an XML file.
1.3 Hierarchical Organization
Modern biology and medicine, like much of society, is currently faced with
overwhelming amounts of raw data being produced by new information-
gathering techniques. In a relatively short period of time information has
gone from being relatively scarce and expensive to being plentiful and inex-
pensive. As a consequence, the traditional methods for dealing with infor-
mation are overwhelmed by the sheer volume of information available. The
traditional methods were developed when information was scarce, and they
cannot handle the enormous scale of information.
The first and most natural reaction by people to this situation is to attempt
to categorize and classify. People are especially good at this task. We are
