Web Taxonomy for referencing external vocabularies
For projects that leverage externally maintained vocabularies, the ideal situation is to be able to reference those external terms rather than attempting to import the entire vocabulary into Drupal, particularly if the vocabulary is frequently updated. Unfortunately, this is an area where there hasn't been a lot of development work. While there was a module that provided integration with the Getty vocabularies (Art and Architecture Thesaurus (AAT), Thesaurus of Geographical Names (TGN), and Union List of Artist Names (ULAN)), it no longer seems to be operational. It was based on the plugin for DBpedia (which does still work), which leaves open some hope that it might be debuggable, if a project chose to undertake that development.
Install and enable the Web Taxonomy module. As of November 2016, only the Web Taxonomy Plugin for DBpedia seems to work. Install and enable it as well, along with the Http Client module, which is a prerequisite.
When you enable the DBpedia plugin, it will create an empty vocabulary, “DBpedia - Web Taxonomy”. Add a new term reference field to the content type where you want to use that vocabulary, and for the widget, choose “Web Taxonomy autocomplete”. For the vocabulary, choose “DBpedia - Web Taxonomy”.
When you create a node with that content type, start typing in the term reference field you created. After a moment, autocomplete suggestions will start appearing from the external vocabulary. After you save the node, the term(s) you added will be saved to Drupal as well and will appear as terms in the “DBpedia - Web Taxonomy” vocabulary when you look at it.