IHE MHD Profile on DocumentReference (DocumentEntry) when used in the Provide Transaction with Minimal Metadata, see Table 3:4.3.1-3.
Profile on DocumentReference based on IHE IT Infrastructure Technical Framework Supplement - Mobile access to Health Documents (MHD) Rev. 2.3. See http://wiki.ihe.net/index.php/Mobile_access_to_Health_Documents_(MHD)
This is the location where you can find your resource using a FHIR client.
The global endpoint is where users can search for all resources in Simplifier. Resources have a globally unique guid Id here.