In the previous chapter we considered how to express the complete content of a document by using more than one heading. Most of the headings used to illustrate Chapter 12 were pre-coordinated headings, combining more than one concept, such as Ecclesiastical embroidery or Wildlife conservation. In fact it's quite hard to find headings that are not pre-coordinated in this way.

There is another way for you to combine concepts in LCSH, and that is through the use of structured headings. A structured heading, like a pre-coordinated heading, has two or more concepts combined, but instead of merging them into a natural language phrase, the conceptual structure is displayed using dashes, rather as we've done with the concept analyses or subject strings.

The normal practice when typing out or entering structured headings is to use a double dash (Bumblebees– –Fiction). This is to distinguish the structured heading from one that simply contains a hyphen (Animalwater relationships or Sugar-beet web-worm).

Structured subject headings fall into three broad categories:

Topical subdivisions

Topical subdivisions, or subject subdivisions, are those subdivisions of a heading that are enumerated in the main list of headings. That is to say, LCSH gives us the subdivision, ready-made for use. Just as in the case of the main headings, valid topical subdivisions are shown in bold. Here are some examples:

This is just a selection of the topical subdivisions under Saturn (Planet). I've left out some of the intervening text, so that you can see the structure more clearly; as a result the BTs and so on are missing here, but you can still see the references from unused terms (non-bold) to preferred terms (bold).