def parse_ext_doc_ref(self, ext_doc_ref_term):
for _s, _p, o in self.graph.triples(<EOL>(ext_doc_ref_term,<EOL>self.spdx_namespace['<STR_LIT>'],<EOL>None)):<EOL><INDENT>try:<EOL><INDENT>self.builder.set_ext_doc_id(self.doc, six.text_type(o))<EOL><DEDENT>except SPDXValueError:<EOL><INDENT>self.value_error('<STR_LIT>', '<STR_LIT>')<EOL>break<EOL><DEDENT><DEDENT>for _s, _p, o in self.graph.triples(<EOL>(ext_doc_ref_term,<EOL>self.spdx_namespace['<STR_LIT>'],<EOL>None)):<EOL><INDENT>try:<EOL><INDENT>self.builder.set_spdx_doc_uri(self.doc, six.text_type(o))<EOL><DEDENT>except SPDXValueError:<EOL><INDENT>self.value_error('<STR_LIT>', '<STR_LIT>')<EOL>break<EOL><DEDENT><DEDENT>for _s, _p, checksum in self.graph.triples(<EOL>(ext_doc_ref_term, self.spdx_namespace['<STR_LIT>'], None)):<EOL><INDENT>for _, _, value in self.graph.triples(<EOL>(checksum, self.spdx_namespace['<STR_LIT>'], None)):<EOL><INDENT>try:<EOL><INDENT>self.builder.set_chksum(self.doc, six.text_type(value))<EOL><DEDENT>except SPDXValueError:<EOL><INDENT>self.value_error('<STR_LIT>', '<STR_LIT>')<EOL>break<EOL><DEDENT><DEDENT><DEDENT>
Parses the External Document ID, SPDX Document URI and Checksum.