The Institute of Electrical and Electronics Engineers Taxonomy

"The IEEE Taxonomy comprises the first three hierarchical 'levels' under each term-family (or branch) that is formed from the top-most terms of the IEEE Thesaurus. In this document these term-families are arranged alphabetically and denoted by boldface type. Each term family's hierarchy goes to no more than three sublevels, denoted by indents (grouping of four dots) preceding the next level terms. A term can appear in more than one hierarchical branch and can appear more than once in any particular hierarchy. The IEEE Taxonomy is defined in this way so that it is always a subset of the IEEE Thesaurus.

The IEEE Thesaurus is a tool to improve and enhance the indexing and retrieval of articles and other material from IEEE periodicals, conferences, standards, and other publications that are made available on IEEE Xplore. It provides a common and consistent language for authors, researchers and online discovery."