Expressing high-level visual concurrency structures in the PFG kernel language

The PFG language is a parallel programming language with graphical syntax. Its formal operational semantics are expressed by the HG model of concurrent real-time software systems. Informally, each procedure in a PFG program is a hierarchical graph expressing the data state and a place-timed Petri net expressing the possible parallel threads of control operating the data state. The author demonstrates how the PFG language, which is sufficient in itself for software construction, can be used as a kernel language for the implementation of higher-level languages. PFG can then be thought of as a graphical assembly language, with the HG model being the virtual machine