Labelling function for classifying keyphrases: a
keyphrase may refer to a terminology or a class to which
the keyphrase belongs, and its name is the same as name of
the class. Thus, the semantics of a keyphrase may relate to
its level of content (or level of its class) such as discipline,
major, subject, theme, topic. To describe the information
that a keyphrase represents a class and level of the class, a
labeling function is used. For example, soft computing
{“terminology”, “major”}.