2 XML Semantics
2.1 The Meaning of Meaning
Semantics is a surprisingly simple notion. It is concerned with when two
terms or statements are thesame. For example, one can write the number
6 in many ways such as: 3 + 3, 06, six and VI. All of these ways to write 6
look different, but they all have the same meaning. The field of semantics
is concerned with extracting a single abstract concept from the many ways
that the concept can be represented, such as words, phrases, sounds, and pic-
tures. Semantics is part of a more general field calledsemioticswhich studies
the relationship between concrete representations and the phenomena in the
world they signify.
Meaning is always relative to a context. For example, “lumbar puncture”
and “spinal tap” are synonymous in the context of medical procedures. How-
ever, they are not synonymous in the context of movies (the latter being the
name of a movie, while the former has never been used in the name of a
movie).
Semantics is often contrasted with syntax. Thesyntaxof a language de-
fines what statements can be expressed in the language. Syntax is concerned
with thegrammarof the language. However, there can be many ways to say
the same thing. The common concept behind the syntactic variations is the
semantics.
The usual method for defining the sameness relationship is to use mathe-
matics. Terminology and statements are then mapped to an abstract mathe-
matical structure, usually called themodel. Two terms or statements are the
same when they map to the same model. Integers, for example, have an
abstract formal model which is used to define their semantics. Medical ter-
minology can be defined using a standard vocabulary such as the Unified
