Elena points out that the SPDX list of licences is very detailed - perhaps too detailed for our purposes. How should we handle this? Define a simpler set?
Proposal: Use the URIs and Identifiers in the SPDX list, noting that a text search for something like 'GPL' would be supported since the Licence class supports both URI and code. So, for example, both of thiese bits of Turtle define licences using the SPDX list and both would be discoverable through a free text search for 'GPL':
<http://www.spdx.org/licenses/GPL-1.0> a dcterms:LicenseDocument ; rdfs:label "GPL-1.0" . <http://www.spdx.org/licenses/GPL-2.0+> a dcterms:LicenseDocument ; rdfs:label "GPL-2.0+" .