What is categorization or classification?
Classification: a partitioning (grouping) of items into
classes with fixed, rigid boundaries.
Classes are defined by necessary and sufficient features;
"necessary" means that the features apply to all items in a class;
"sufficient" means that enough features are provided to distinguish
the class from other classes.
Classification scheme: a hierarchy of classes.
A class is a subclass of another class (superclass)
if all the items of the subclass also belong to the superclass.
The classes at the lower levels of the hierarchy are specialized
or concrete; the classes at the higher levels are
general or abstract.
Classes are mutually exclusive, which means that an item
cannot belong to more than one class on each level of a classification
Examples of classification schemes
library classification schemes; biological taxonomies; directories
on the WWW; linguistic thesauri; philosophical classification
Categories are loose groupings of items; they are less
rigid than classes.
They are non-exclusive, which means
that an item can belong to many categories at the same time.
The boundaries among categories are not fixed, which means that
it is sometimes not clear whether an item belongs to a category
Categories usually have some prototypical members that
are at the conceptual "center" of a category. The membership is
graded, which means some items are "better" members of
categories than others.
There may not be features that are shared by all members of a
category, but members of a category usually show some similarity
to each other.
The cultural and cognitive nature of classification and
Classification and categorization usually
depend on a social, linguistic and cultural context. It is therefore
very difficult (or impossible) to build "universal" schemes that
cover all human knowledge.
Examples: Labov's cups; Berlin & Kay's basic color terms;
prototypical class/category members, such as robin, pigeon for "bird";
chair, table for "furniture"
Philosophical theories of classification and concepts
Philosophical theories of classification: Aristotle; Smith & Medin.
Rosch's "Prototype Theory" for categories.