On Disallowing Punctual Intervals in Reflexive Semantics of Halpern-Shoham Logic

Abstract

Halpern-Shoham logic (HS) is a very expressive and elegant formalism for interval temporal reasoning in which the satisfiability problem is undecidable. One of the methods to obtain HS-fragments of lower computational complexity is to adopt the softened (reflexive) seman- tics of the accessibility relations. In the paper we consider disallowing punctual intervals in reflexive semantics. We show that in this case we gain additional expressive power, which over discrete orders of time points results in PSpace-hardness of the Horn fragment of HS without diamond modal operators is and in undecidability of the core fragment of HS.