MASL is a Shlaer-Mellor model and action specification language that can textually represent all of the executable elements of Object Oriented Analysis models. A model of MASL has been created. It is an OOA of MASL, a meta-model of the modeling language.
The OOA of MASL is semantically equivalent to the xtUML meta-model, OOA of OOA. However, since the two languages were modeled independently, the meta-models are not identical. Here are statistical comparisons between the subsystems of OOA of MASL and of xtUML. It is clear from the statistics that the MASL action language has much richer support for expressions compared to the Value subsystem of xtUML.
The source OOA of MASL can be found here.