Action Language BC+: Preliminary Report

ABSTRACT. Recently, action language $\cal BC$, which combines the attractive features of action languages $\cal B$ and $\cal C$+, was proposed. While $\cal BC$ allows Prolog-style recursive definitions not available in $\cal C$+, it is less expressive than $\cal C$+ in other ways, such as inability to express non-Boolean and non-exogenous actions. We propose a new action language called $\cal BC$+, which encompasses $\cal BC$ and $\cal C$+. The syntax of $\cal BC$+ is essentially identical to the syntax of $\cal C$+, but its semantics is defined in terms of a translation into propositional formulas under the stable model semantics similar to $\cal BC$. By understanding the formulas in causal laws in terms of the stable model semantics, this approach allows many useful ASP constructs, such as choice rules and aggregates, to be directly usable in language $\cal BC$+, and exploits computational methods available in ASP solvers.