Another important information structure often used in technical writing is classification.

What is Classification?

In some technical reports, certain paragraphs or sections use a kind of writing and pattern of organization known as classification. Classification means either (1) explaining which class a thing belongs to or (2) dividing a group of things into classes. You may find that classification is an effective way to present background information to your readers.

See the complete example of a division-type classification.

True classification. You are "classifying" (in the strict dictionary sense of the term) when you place an object, action, or person in one of several classes. For example, the XYZ Corporation may have just come out with its new ABC computer but cannot decide whether to classify it as a laptop or a notebook computer. A botanist may have discovered a new species of fungus and must now decide how to classify it. Written documents on these questions would resemble comparison because features of the new item (the computer or the fungus) must be compared to those of the established classes. The Jupiter example in the following shows an example of a true classification in which the writer shows why the object belongs to one specific category.

Division. Classification can also refer to breaking a thing down into its types, classes, categories, or kinds and then discussing each one. For example, computers for some time now have been divided into several classes: minicomputers, microcomputers, and macrocomputers. And, if you have ever taken biology, you know that terrestrial life is divided into into plant and animal "kingdoms"; the kingdoms, broken down into phyla (the plural of phylum); phyla, into classes; classes, into families; families, into genera; and genera, into species. Each of these divisions—except perhaps the last—represents a grouping of types.

Several key words indicate that classifications are being discussed: classes, kinds, types, categories, sorts, or groups. Classification can be quite useful in technical reports: it breaks the discussion of a subject into smaller chunks, and it can make the job of evaluation and selection much easier.

Jupiter can be classed as a Jovian planet because of its size and its average density. Indeed Jupiter is the largest planet in our solar system (as shown in Figure 16) and one of the brightest objects in the sky, having attained a magnitude of -2.5, more than a full magnitude brighter than Sirius, the brightest star in the sky. Jupiter's brightness results from its great size of course but also from its high reflectivity: it reflects about 44 percent of the light it receives. The size and composition of Jupiter's interior are open to much speculation. Some astronomers picture the interior as having a radius of over 30,000 miles and as possibly being composed of liquid hydrogen. The core is small and dense and may contain iron silicates. The other Jovian characteristic of the planet is its density. Even though its diameter is only 11 times that of the Earth, its total volume is 11 × 11 × 11, or over a thousand times that of Earth.


Figure 16. Jupiter

More graphically, over 1000 Earths could be packed into the space occupied by Jupiter.

"True" classification. In this example, the writer argues that Jupiter should be categorized as a "Jovian"-type planet. This is one type of classification; in the other, you divide a collection of things into categories, or types.

How to Identify Classes and the Principle of Classification?

Once you know what you are going to divide into classes, your next step is to identify the classes and the principle of classification. For example, if you were classifying dialysis machines (used to treat people with kidney disease), you might list these classes:

The principle of classification is the design of the structure through which blood is filtered.

The principle of classification then is the method you use to sort the items into classes. If you sorted marbles into red, green, and blue ones, you'd be using color as the principle of classification. You must be careful to use only one principle of classification at a time. For example, you couldn't sort your marbles by color and size—you might have some big red ones and some small red ones!

Here are some additional examples of classifications and their principles:

TopicClassesPrinciple of classification
Electrical circuits Series
Parallel
Series-parallel
Pathway of electrical current
AnemiasBlood-loss anemia
Iron-deficiency anemia
Pernicious anemia
Main cause of the anemia
Hurricane track prediction methods Total climatology and persistence methods
Particular climatology
and persistence method
Circulation and climatology method
Dynamic model method
Combination of hurricane characteristics
Wind machines Lift machines
Drag machines
Interaction between the wind and propeller blade

How to Discuss the Classes?

When you write the discussion of the individual classes, you must choose sources of discussion that enable you to explain each class fully, add comparisons so that readers can see the differences between the classes, and plan for the length of your classification.

Choosing sources of discussion. Writing the discussion of individual classes is much the same as it is with extended definitions: you combine a variety of sources to explain the classes fully—see the checklist for a listing of these sources. To discuss the three types of dialysis machines for victims of kidney disease, you might use these sources:

Classification of dialysis machines
DefinitionKidney disease
DescriptionMain components of the different dialysis machines
ProcessHow the different machines operate
ComparisonAdvantages and disadvantages of these machines

Of course, some classifications may use only one kind of writing. For example, in the discussion of different hurricane track prediction methods, the discussion would most likely be process—step by step how the methods work.

Adding comparisons. No matter which sources you use in discussing the classes, comparison is an important ingredient. It helps readers distinguish the different classes from each other. Check out the following example of how comparisons work in classifications.


Comparisons used in classification. Comparing the types to each other gives readers a clearer sense of the types as well as their distinguishing features.

Short and extended classifications. In short classifications, an overview of the types is packed into one sentence or into one paragraph. In an extended classification, you might have one or more paragraphs on each type. For an extended classification, you'll use a paragraph or more to discuss each of the classes, and a separate paragraph to introduce these classes—as illustrated in the extended classification in the following.


Single-paragraph classification. All the classes are discussed briefly in this one section.


Extended classification with classes treated each in their own paragraphs


Schematic view of classification. Remember that this is just a typical or common model for the contents and organization—many others are possible.

How to Format for Classifications?

Classifications don't call out for any special format; just use headings, lists, notices, and graphics as you would in any other technical document. For details, see: