def resolve_imports(self, imports, import_depth, parser=None):
        """Import required ontologies.
        """
        if imports and import_depth:
            for i in list(self.imports):
                try:

                    if os.path.exists(i) or i.startswith(('http', 'ftp')):
                        self.merge(Ontology(i, import_depth=import_depth-1, parser=parser))

                    else: # try to look at neighbouring ontologies
                        self.merge(Ontology( os.path.join(os.path.dirname(self.path), i),
                                             import_depth=import_depth-1, parser=parser))

                except (IOError, OSError, URLError, HTTPError, _etree.ParseError) as e:
                    warnings.warn("{} occured during import of "
                                  "{}".format(type(e).__name__, i),
                                  ProntoWarning)
Import required ontologies.