STI Tools

Learn more about how to use and access NASA STI tools, including NASA Thesaurus, NASA Scope and Subject Category Guide, and NASA Thesaurus Machine Aided Indexing (MAI).

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NASA Thesaurus
The NASA Thesaurus contains the authorized NASA subject terms used to index and retrieve materials in the NASA Technical Reports Server (NTRS) and the NTRS Registered (Formerly NA&SD). The scope of this controlled vocabulary includes not only aerospace engineering, but all supporting areas of engineering and physics, the natural space sciences (astronomy, astrophysics, planetary science), Earth sciences, and the biological sciences. The NASA Thesaurus contains over 18,400 subject terms, 4,300 definitions, and more than 4,500 USE cross references.

  • NASA Thesaurus Data File
    The NASA Thesaurus Data File contains all valid terms and hierarchical relationships, USE references, and related terms in machine-readable form. The Data File is available in the following formats: RDF/SKOS, RDF/OWL, ZThes-1.0, and CSV/TXT.

    Review format samples, and download full data file.


NASA Scope and Subject Category Guide

The NASA Scope and Subject Category Guide is a scheme of 76 subject categories that permits high-level subject classification of scientific and technical information. It provides scope notes, listing of subtopics, cross references and an index of nearly 3,000 research topics of particular interest to NASA linked to the appropriate subject categories.


NASA Thesaurus Machine Aided Indexing (MAI)
Machine Aided Indexing (MAI) is an aid to indexing technical literature for the NTRS Registered (formerly known as the NA&SD). The web-based application was designed to provide authors, editors, information analysts, and others with a convenient, fully interactive tool for determining the subject content of documents, and identifying keywords and terms for various uses. The terms of the NASA Thesaurus serve as the foundation for the extensive knowledge base used by MAI. Using this established vocabulary of terms, MAI provides valuable assistance in assuring that technical reports and other STI documents are uniformly and consistently accessible.



The NASA STI Program produces two daily feeds comprised of bibliographic information loaded to the NASA Technical Reports Server during the prior day.