def _aggregate_text(self, offering):
"""
Create a single string for creating the index by extracting text fields
from the USDL document of the offering
"""
graph = rdflib.ConjunctiveGraph()
generator = USDLGenerator()
graph.parse(data=generator.generate_offering_usdl(offering)[0],
format='application/rdf+xml')
text = offering.name
for s, p, o in graph:
if isinstance(o, rdflib.Literal):
text += ' ' + unicode(o)
return text
