def get_source(self):
raise Unimplemented()<EOL>
Gets the Resource of the source of this asset.

        The source is the original owner of the copyright of this asset
        and may differ from the creator of this asset. The source for a
        published book written by Margaret Mitchell would be Macmillan.
        The source for an unpublished painting by Arthur Goodwin would
        be Arthur Goodwin.

        return: (osid.resource.Resource) - the source
        compliance: mandatory - This method must be implemented.