About: http://webisa.webdatacommons.org/188482445

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	You might want to return empty string for c, and undefined for something that is not there at all for example d.
http://www.w3.org/ns/prov#wasQuotedFrom	stackoverflow.com