The case for coordination
[This page refers to the mechanism of combination/composition/coordination, that is the general idea of synthesizing new concepts from the ones that already exist in a concept cheme, making these former concepts explicit components of the newly built one. This overlaps with what is refered to as pre/post-coordination in traditional indexing terminology.]
Several concept schemes provide with the ability to build new concepts from existing ones, in an articulated way. When indexing (or extending the central authority file for a concept scheme), one can take two or more concepts, and combine them to form a new concept which expresses a relationship between its components. It must be noticed that several kind of combination mechanisms can co-exist in a same concept scheme, allowing to denote specific kind of relations between the components.
Combination allows to match a greater number of indexing needs, while keeping the size and structure of the concept scheme tractable. It also allows for better, more structured rendering of complex subjects, eventually leading to automatic processing of these.
Typical examples are:
auxiliaries in Iconclass, EucIconclassDetailed
auxiliaries in UDC, EucUDC
subdivisions in RAMEAU, EucRameau
One caracteristic of these approaches is that they are controlled. Not all the concepts can be used in combination with others. Escpecially in directed combination approaches (when there is a distinction between a main concept and qualifier ones) this has eventually lead to the introduction of specific conceptual units that can only be used in combination with self-standing concepts...
Cf. current SKOS issue on Coordination http://www.w3.org/2004/02/skos/core/proposals.html#coordination-8