def format_graph_uri(uri, server_url):
    """Format a GRAPH IRI if its belong to the same server than the current one"""
    if not server_url.endswith('/'):
        server_url += '/'
    if uri.startswith(server_url):
        index = uri.index(server_url)
        return uri[index + len(server_url):]
    return '_:UnkownGraph'