A modular formal semantics for Ptolemy

Abstract

Ptolemy is an open-source and extensible modeling and simulation framework. It offers heterogeneous modeling capabilities by allowing different models of computation, both untimed and timed, to be composed hierarchically in an arbitrary fashion. This paper proposes a formal semantics for Ptolemy which is modular, in the sense that atomic actors and their compositions are treated in a unified way. In particular, all actors conform to an executable interface that contains four functions: fire (produce outputs given current state and inputs), postfire (update state instantaneously), deadline (how much time the actor is willing to let elapse) and time-update (update state with passage of time). Composite actors are obtained from composition operators that in Ptolemy are called directors. Different directors realize different models of computation. This paper defines formally the directors for the following models of computation: Synchronous-Reactive, Discrete Event, Continuous Time, Process Networks, and Modal Models.

Hybrid co-simulation: it’s about time

“…In that same paper, small extensions to the standard were proposed with the goal of enhancing the standard's ability to handle mixed discrete and continuous behaviors. Some of these extensions are reminiscent of functions included in the actor interface in the modular formal semantics of the Ptolemy tool [48]. For instance, the "getMaxStepSize" function of [7] is similar to the D ("deadline") function of [48].…”

“…Some of these extensions are reminiscent of functions included in the actor interface in the modular formal semantics of the Ptolemy tool [48]. For instance, the "getMaxStepSize" function of [7] is similar to the D ("deadline") function of [48]. Followup work includes [8], which proposes a collection of test cases together with acceptance criteria that can be used to determine whether a hybrid co-simulation technique is acceptable.…”

Bridging the semantic gap between heterogeneous modeling formalisms and FMI

“…DE is one of the models of computation supported in a number of languages and tools such as ns-3, VHDL, SimEvents, and Ptolemy [7]. The semantics of DE have been formalized in various papers, e.g., [12,21,20]. Here we show how to encode typical DE actors such as Periodic Clock and Constant Delay as FMUs, following principles similar to those presented in [21].…”

“…We will solve this problem following the same approach as in [21], namely, by introducing a special value denoted absent, which models the absence of an event at a certain point in time. Output variables that carry events will have value absent most of the time, except at those times when an event occurs, in which case the value of the output variable is the value of the occurring event.…”

“…The components in Ptolemy II are implemented in Java and called actors and have similar structures as FMUs, but with a different interface. A formalization of Ptolemy's actor interface and encodings of various models of computations have been proposed in [21].…”