bool IsResourceWellFormed( ExternalResourceReference extRef )
Different servers will have different requirements.
A server which loads references from a website might require that the reference map contain a key called "URL" and a value that is a valid URL.
A server which loads references from a network drive might require a key called "Drive" with a value that represents a drive name, plus a key called "Path" with a value that corresponds to a path relative to the root of the drive.
This function should not check that the resource exists on the server. It should only check that the resource is formatted correctly.