The Meaning of Ordered SOS

Structured Operational Semantics (SOS) is a popular method for defining semantics by means of deduction rules. An important feature of deduction rules, or simply SOS rules, are negative premises, which are crucial in the definitions of such phenomena as priority mechanisms and time-outs. Orderings on SOS rules were proposed by Phillips and Ulidowski as an alternative to negative premises. The meaning of general types of SOS rules with orderings has not been studied hitherto. This paper presents satisfactory ways of giving a meaning to general SOS rules with orderings. We also give semantics-preserving transformations between the two paradigms, namely, SOS with negative premises and SOS with orderings.