NASA - National Aeronautics and Space Administration   + Visit NASA.gov
+ Contact the NASA Curator

For Developers

The NASA Taxonomy has the following technical components used for implementation:

  • NASA Core Metadata Specification

    Metadata is commonly defined as "data about data". Metadata is expressed as metadata elements, or fields, which have values. In some cases the values come from a controlled vocabulary known as a taxonomy.

  • Taxonomy DTD
  • Taxonomy SKOS Files
  • Editorial Style Guide

    Taxonomies use formal vocabulary terms that are documented in an editorial style guide. If you wish to write your data according to the NASA Editorial Style Guide, find the expression rules here.

Metadata DTD File

Back to Top

rdf_metadata.dtd
This is a simple DTD for an RDF-compliant metadata format. This format is not an offical NASA standard. Instead, it is a recommendation from the NASA Taxonomy Project on what a NASA standard metadata format might look like. The members of the Taxonomy Project recognize that other projects and Centers will have their own formats, and hopes for a dialog in order to come up with an official NASA standard. The format began with the Dublin Core Specification, added some of the Dublin Core extensions, and added new elements in a NASA namespace for fields whose values come from the NASA Taxonomy.

Taxonomy SKOS Files

Back to Top

The NASA Taxonomy is expressed in an XML language called SKOS which stands for Simple Knowledge Organizing System.

The SKOS Core is a model and an RDF vocabulary proposed by the W3C for expressing the basic structure and content of concept schemes such as thesauri, classification schemes, subject heading lists, taxonomies, other types of controlled vocabulary.

The SKOS Core Vocabulary is an application of the Resource Description Framework (RDF), that can be used to express a concept scheme as an RDF graph. Using RDF allows data to be linked to and/or merged with other data, enabling data sources to be distributed across the web, but still be meaningfully composed and integrated.

SKOS files are made to be referred to as URIs. This allows abstraction of the meaning and provides extra flexibility to the vocabularies. Feel free to refer to the URIs in your code or to download any of the SKOS files below for re-use.