def get_concept_scheme(rdf):
<EOL>for s, o in rdf.subject_objects(SKOS.inScheme):<EOL><INDENT>if not isinstance(o, Literal):<EOL><INDENT>rdf.add((o, RDF.type, SKOS.ConceptScheme))<EOL><DEDENT>else:<EOL><INDENT>logging.warning(<EOL>"<STR_LIT>", o)<EOL><DEDENT><DEDENT>css = list(rdf.subjects(RDF.type, SKOS.ConceptScheme))<EOL>if len(css) > <NUM_LIT:1>:<EOL><INDENT>css.sort()<EOL>cs = css[<NUM_LIT:0>]<EOL>logging.warning(<EOL>"<STR_LIT>"<EOL>"<STR_LIT>", cs)<EOL><DEDENT>elif len(css) == <NUM_LIT:1>:<EOL><INDENT>cs = css[<NUM_LIT:0>]<EOL><DEDENT>else:<EOL><INDENT>cs = None<EOL><DEDENT>return cs<EOL>
Return a skos:ConceptScheme contained in the model.

    Returns None if no skos:ConceptScheme is present.