Frequently Asked Questions about the USGS Thesaurus

Terms represent concepts, but it is the concepts themselves and their relationships, not the terms, that constitute the thesaurus.

Terms are related to one another in three different ways:

Hierarchy

A term always has an "is a" relationship with its broader term (BT); a narrower term (NT) can always be said to be "a type of", "a part of", or "an instance of" the parent term.

Preference

For a given concept, one term is chosen as the preferred term or label, and is referred to as the descriptor. Other terms that refer to the same concept are referred to as lead-in terms or non-preferred terms. A non-preferred term is not necessarily a synonym of the preferred term.

Generic relationships

Where concepts are related in some way that cannot be expressed as an "is a" sentence, the thesaurus simply connects one term to another without specifying the nature of the relationship. This is different from more elaborate knowledge-management systems such as topic maps or ontologies in which such generic relationships are always identified and categorized.

Thesaurus interfaces such as Science Topics are not intended to replace traditional search or browse interfaces. In concert with the new "USGS by State" and "About USGS" sites, they supplement existing navigational aids to USGS web information.

1. The USGS Thesaurus is designed to conform with a recognized standard, ANSI/NISO Z39.19. This standard has been in widespread use throughout the information science community for many years.
2. The thesaurus is broad and shallow. It is not intended to enumerate or distinguish the fine details of USGS science, and it is not intended to duplicate detailed search within a scientific database on a particular topic that would ordinarily be provided by a web site developer.
3. The thesaurus is explicitly intended for use in a web browsing environment. Consequently it is strictly hierarchical. No term has more than one broader term; alternative broader terms are shown as related terms instead. Also the number of top terms is intentionally kept small to enable browse interfaces to function well.
4. The thesaurus is monolingual. Foreign-language equivalents are possible in principle but have not been incorporated into the current design.
5. The thesaurus is intended to cover only those facets of information for which other controlled vocabularies were either not available or were not optimal for categorizing USGS information. Consequently the thesaurus does not include place names, types of named geographic features, detailed biological taxonomy, chemical and mineral names, USGS publication series names, or names of organizational units and programs.

Development methods

Specialists recognize two different strategies for building controlled vocabularies: top-down, in which terms and their relationships are defined intuitively prior to their direct application in an indexing situation; and bottom-up, in which terms and relationships are added to the vocabulary in the process of indexing. But the same specialists also recognize that most vocabularies are developed using a combination of these two abstract approaches. We developed the USGS thesaurus using this combined strategy. Beginning by simply listing lots of important terms, we grouped those terms using a card-sorting procedure, and then refined the hierarchy with intuitive processes (that is, by relying on what we know). Subsequent revisions have occurred by group deliberation.

Preliminary development of the thesaurus was conducted using commercial software (MultiTES) by a contractor. Subsequent development and revision has occurred in a web-based database application developed by the group meeting the specific needs of this project.

Review of existing controlled vocabularies

We examined many similar controlled vocabularies of various types before and during this process. Examples are the GEOREF thesaurus produced by the American Geological Institute, the CERES thesaurus ( http://ceres.ca.gov/thesaurus/) the Geographic Names Information System (GNIS), the Integrated Taxonomic Information System (ITIS), the categorization scheme used in the Marine Realms Information Bank (http://mrib.usgs.gov/), and numerous smaller or more specialized vocabularies such as glossaries of scientific and technical terms presented on USGS web sites.

Alphabetical listings of the thesauri are generated periodically, and provided here compressed:

• USGS Thesaurus
• Alexandria Digital Library Feature Type Thesaurus
• U.S. National Parks
• Wildlife Refuges
• Lithologic classification of geologic map units

ITIS is maintained separately by the USDA.