Subclause 6.2 Changes to Adopted OMG Specifications of the Precise Semantics for UML State Machines (PSSM) Beta 1 specification document (ptc/17-04-04) states:
The PSSM syntax is a subset of the UML 2.5.1 abstract syntax metamodel, and the required functionality formalized in PSSM is taken from that specified in UML 2.5.1. However, PSSM is also semantically based on fUML and PSCS. But the current versions of these standards, fUML 1.2.1 and PSCS 1.0 are based on UML 2.4. In order to avoid inconsistency, particularly given the sweeping reorganization of the UML abstract syntax metamodel adopted in UML 2.5, the fUML and PSCS syntax and semantics models have been migrated to UML 2.5.1 for use with PSSM, but with no change to their functionality. In addition, the fUML and PSCS models have been updated to use an approach for identifying and constraining their syntax subsets that is consistent with that used in PSSM.
In adopting this specification, the PSCS RTF was directed to update the PSCS specification consistent with the migration of fUML syntax and semantics models top UML 2.5.1. Since the adoption of PSSM, PSCS 1.1 has been approved as the current version of PSCS, so the PSCS 1.2 RTF now needs to carry out the migration of PSCS 1.1 to UML 2.5.1 for PSCS 1.2.