// a provence-generating activity
message Activity
 {
  id String = 1
  optional startedAtTime Date = 2
  optional endedAtTime Date = 3
  optional wasInformedBy Activity = 4
  optional wasAssociatedWith Agent = 5
  optional used String = 6
  optional description String = 7
 }
// a provence-generating agent
message Agent
 {
  id String = 1
  optional actedOnBehalfOf Agent = 2
  optional wasInformedBy Activity = 3
 }
