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CLASSIFYING AND SEQUENCING: Introduction
Jim Mariner


OBJECTIVES

  1. To identify properties that can be used to classify in a binary classification system;
  2. To construct a multistage (dichotomous) classification system for a set;
  3. To identify properties by which a set can be ordered in a serial fashion and order a set accordingly.

BACKGROUND

In a binary classification system, a set of objects is divided into two subsets on the basis of whether each object has or does not have a particular property. To construct a binary classification system, you must first identify a property which some of the objects have but that none of the other objects have. You then group all the objects displaying that property in one set and all of the objects in the other set. For example, a biologist might classify living things into two groups: plants and non-plants. In this case, plants would be the group that displays certain properties unique to plants. the other group does not have those characteristics. You must be certain that all the objects in the original set can be grouped into one and only one of the two subsets.

This same system is used to develop a multistage classification scheme. The only difference is that each subset is continually divided into two additional subsets in a binary manner until there is only one member in the subset. An elm tree, for example, would only be one member of the subset Plant. But plants can be further divided into subsets: green plants and plants that are not green. The green subset would include, along with elm trees, all of the green plants with which we are familiar, but it would exclude other types of plants (fungi, etc). The subset of green plants can be further subdivided a number of times until only a group that we recognize as elm trees remain in the subset.

It is sometimes necessary to arrange (or order) objects according to the extent that they display a particular property. This is called serial ordering. Depending on the purpose of the classification, objects may be arranged on the basis of size, shape, color, or a variety of other features. In a hardware store, nails are ordered on the basis of size. Paints can be arranged by the size of the can or by color. Clothing stores also arrange merchandise in a serial fashion according to size.

There are three parts to this exercise: (A) identifying characteristics of a binary system of classification, (B) constructing and using a dichotomous classification system, and (C) serial ordering.

Part A: Binary System | Part B: Dichotomous System | Part C: Sequencing


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