Animal Disease Thesaurus

"The first section is an alphabetical arrangement of keyword terms. In this section the first 6 digits represent the code number, and the next 2 digits indicate the category in the hierarchical section of the Thesaurus. Digits are followed on the same line by corresponding keywords. The first word is the coded keyword term or concept, followed by a slash //, which separates the coded work from its next hierarchical level. (One, two, or three level hierarchical arrangement.)

The second section is the hierarchical arrangement of the coded terms. It is divided into 10 categories. Each category has up to 3 levels of keyword terms or concepts, each level intended from the preceding level and preceded by a code number."