The rule of three in indexing
When many descriptors are discussed in a document, it may not be possible to index each one without using too much depth. Then, the “rule of three” applies: if more than three concepts are selected and they can be covered by a single broader term, that broader term should be chosen for indexing.
Consulting the hierarchy of concepts is essential to achieve this.
For example, in a document that deals equally with lizards, snakes and turtles, the indexer should check the hierarchy of each of these possible descriptors.
Since LIZZARDS, SNAKES and TURTLES are positioned as “siblings” under REPTILES in the same hierarchy, instead of indexing all three terms, only the most general descriptor, REPTILES, should be used.
See the illustration below:
Category: DeCS tips
