if frequency is not None:
frequency_details = BNode()
value_node = BNode()
duration_desc_node = BNode()
# AccrualPeriodicity
g.add((dataset_ref, DCT.accrualPeriodicity, frequency_details))
# Frequency
g.add((frequency_details, RDF.type, DCT.Frequency))
# Value
g.add((value_node, RDF.type, RDF.value))
g.add((frequency_details, RDF.value, value_node))
# DurationDescription Label and Time:X
g.add((value_node, TIME.DurationDescription, duration_desc_node))
g.add((duration_desc_node, RDF.type, TIME.DurationDescription))
g.add((duration_desc_node, RDFS.label, Literal(frequency)))
g.add((duration_desc_node, TIME.days, Literal(1)))