@classmethod
def _urlize_accession(cls, accession):
    """Return an URL version of `accession`.

        Arguments:
            accession (str): an ontology accession (e.g. *MS:1000031*), from
                one of the following ontologies: **MS**, **UO**, or **IMS**.

        """
    try:
        namespace, id_ = accession.split(':', 1)
        if namespace in {'MS', 'UO'}:
            url = 'http://purl.obolibrary.org/obo/{}_{}'
        elif namespace == 'IMS':
            url = 'http://www.maldi-msi.org/download/imzml/imagingMS.obo#{}:{}'
        else:
            url = '{}:{}'
        return url.format(namespace, id_)
    except ValueError:
        return accession
