Using External Ontologies on AWS Neptune

The short answer is that you want to use SPARQL Update LOAD to actually load the external ontology into Neptune, something like this:

LOAD <http://www.w3.org/1999/02/22-rdf-syntax-ns#
>```

There are, however, a couple of caveats/details to be considered:  
  
You must "punch a hole" so that Neptune can actually reach out of your VPC. Do this using a NAT Gateway. This document is helpful: https://aws.amazon.com/premiumsupport/knowledge-center/internet-access-lambda-function/  
  
Also note that Neptune uses HTTP content negotiation to fetch RDF content in the right format. See this (section "Media-types that SPARQL UDATE LOAD can import"): https://docs.aws.amazon.com/neptune/latest/userguide/sparql-media-type-support.html  
  
Some external ontologies may not be "content-negotiable", instead the external server uses some HTTP redirect code to inform the client where the actual RDF content is. Neptune does not handle these situations, so you may need to test (say, using curl) how the external server actually responds. I believe SKOS, for example, is set up this way.