Understanding RDF, RDFS, and OWL: References vs Dependencies

The references are not dependencies in the same sense as you would have with software libraries. If you load the RDF, RDFS, and OWL vocabularies (from their respective URLs at W3C), you can do it in any order. The references are URIs that identify nodes, and since in RDF they are mere names, you can refer to one without having its definition present.