PropertyValue
http://www.w3.org/1999/02/22-rdf-syntax-ns#type
http://www.w3.org/ns/prov#value
  • In these versions, a valid ???null??? signal is a signal that has not yet evaluated and whose value is not required to accomplish a given function.) In versions that do not support a ???null??? signal, an N-nary signal that does not have a high voltage asserted on any wire is considered to be an invalid signal.
http://www.w3.org/ns/prov#wasQuotedFrom
  • google.com