Reification

Fluents are Truth Functional

• Example: waterLevel(2)

• Event calculus uses holdsAt/2 to situate fluents in time, e.g.,
  holdsAt(waterLevel(2),3)
• waterLevel(2) has been reified to a term

Sorts and Reification

• Three sorts: fluent, event, time
• DEC predicates and functions have a sort signature,
  e.g., holdsAt(fluent,time)

• Sort conformance ensured by structure of first-order system (non-explicit)

• Does not allow deduction of negation of anomalies, e.g.,
  ~holdsAt(tapOn,waterLevel(3))