def METHOD_NAME(self) -> Union[FilePathStr, URIStr]:
    """Get the reference URL that is targeted by this artifact entry.
    Returns:
        (str): The reference URL of this artifact entry.
    Raises:
        ValueError: If this artifact entry was not a reference.
    """
    if self.ref is None:
        raise ValueError("Only reference entries support ref_target().")
    if self._parent_artifact is None:
        return self.ref
    return self._parent_artifact.manifest.storage_policy.load_reference(
        self._parent_artifact.manifest.entries[self.path], local=False
    )