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Obstacles to Re-use of Information and Application Independence

The second major problem with enumerative classifications is that they must be designed for a single purpose or a small group of closely related purposes. Re-use of enumerative classifications in independent applications has proved difficult or impossible.

Enumerative classification systems inevitably require developers to choose in advance which concepts will be enumerated, since the total of all such concepts is too large to manage. Most enumerative systems use only a simple hierarchy and have conventions such as a fixed depth of classification, upper limits to the number of concepts at any given level of the classification, or limits on concepts having multiple ‘parents’. Observing such conventions requires further choices. Such choices can be tuned to any one use, but they limit the usefulness of the classification system for other purposes.

Since traditional systems have only a single hierarchy, be it single or multiple, the different classification criteria must be mixed within this single structure. Two types of mixing can be identified:

  1. Mixing of different kinds of concepts and different compositional principles in a single hierarchy — for example mixing of the reason for an action and the nature of the action in the same hierarchy, e.g.

    respiratory condition
    .. cough
    .... cough reported by patient
    .... cough observed by doctor
    .... productive cough

  2. Mixing of part-whole and generic relations, e.g.

    Bone
    .. Flat Bone
    .. Long Bone
    .... Femur
    ...... Periosteum
    ...... Subperiosteum
    ...... Shaft
    ........ Proximal third of shaft of bone
    ...... Marrow

In each case the order in which the different criteria are applied and which combinations of characteristics are used in abstractions depends on the use to be made of the information. Making such decisions in advance restricts the usefulness of the information for other purposes.

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