Add prov_was_derived_from property and StepRetroProv

Author: svenvanderburg

fairworkflows/prov.py

@@ -7,11 +7,23 @@
 class RetroProv(RdfWrapper):
     def __init__(self, prov_was_derived_from, log_message: str):
         super().__init__(uri=None, ref_name='retroprov')
-        self.rdf.add((self.self_ref, rdflib.RDF.type, namespaces.PROV.Activity))
-        self.rdf.add((self.self_ref, namespaces.PROV.wasDerivedFrom,
-                      rdflib.URIRef(prov_was_derived_from)))
+        self.set_attribute(rdflib.RDF.type, namespaces.PROV.Activity)
+        self.set_attribute(namespaces.PROV.wasDerivedFrom, rdflib.URIRef(prov_was_derived_from))
         self.rdf.add((self.self_ref, rdflib.RDFS.label, rdflib.Literal(log_message)))
 
+    @property
+    def prov_was_derived_from(self):
+        """Refers to URI of object that this provenance was derived from.
+
+        Matches the predicate prov:wasDerivedFrom associated to this retrospective provenance
+        object
+        """
+        return self.get_attribute(namespaces.PROV.wasDerivedFrom)
+
+    @prov_was_derived_from.setter
+    def prov_was_derived_from(self, value):
+        self.set_attribute(namespaces.PROV.wasDerivedFrom, rdflib.URIRef(value), overwrite=True)
+
 
 class WorkflowRetroProv(RetroProv):
     def __init__(self, prov_was_derived_from, log_message):
@@ -22,3 +34,14 @@ def __str__(self):
         s = f'Workflow retrospective provenance.\n'
         s += self._rdf.serialize(format='trig').decode('utf-8')
         return s
+
+
+class StepRetroProv(RetroProv):
+    def __init__(self, prov_was_derived_from, log_message):
+        super().__init__(prov_was_derived_from, log_message)
+
+    def __str__(self):
+        """String representation."""
+        s = f'Step retrospective provenance.\n'
+        s += self._rdf.serialize(format='trig').decode('utf-8')
+        return s