Soundness-preserving refinements of service compositions

Soundness is one of the well-studied properties of processes; it denotes that a final state can be reached from every state that is reachable from the initial state. Soundness-preserving refinements are important for enabling the compositional design of systems. In this paper we concentrate on refinements of service compositions. We model service compositions using Petri nets, and consider specific pairs of places that belong to different services. Starting from a sound service composition, we show how to check whether such a pair of places can be refined by another sound service composition, so that soundness is preserved through the refinement

Soundness-preserving composition of synchronously and asynchronously interacting workflow net components

In this paper, we propose a compositional approach to construct formal models of complex distributed systems with several synchronously and asynchronously interacting components. A system model is obtained from a composition of individual component models according to requirements on their interaction. We represent component behavior using workflow nets - a class of Petri nets. We propose a general approach to model and compose synchronously and asynchronously interacting workflow nets. Through the use of Petri net morphisms and their properties, we prove that this composition of workflow nets preserves component correctness.Comment: Preprint of the paper submitted to "Fundamenta Informaticae

Compositional Semantics of Finite Petri Nets

Structure-preserving bisimilarity is a truly concurrent behavioral equivalence for finite Petri nets, which relates markings (of the same size only) generating the same causal nets, hence also the same partial orders of events. The process algebra FNM truly represents all (and only) the finite Petri nets, up to isomorphism. We prove that structure-preserving bisimilarity is a congruence w.r.t. the FMN operators, In this way, we have defined a compositional semantics, fully respecting causality and the branching structure of systems, for the class of all the finite Petri nets. Moreover, we study some algebraic properties of structure-preserving bisimilarity, that are at the base of a sound (but incomplete) axiomatization over FNM process terms.Comment: arXiv admin note: substantial text overlap with arXiv:2301.0448

A Local-Time Semantics for Negotiations

Negotiations, introduced by Esparza et al., are a model for concurrent systems where computations involving a set of agents are described in terms of their interactions. In many situations, it is natural to impose timing constraints between interactions -- for instance, to limit the time available to enter the PIN after inserting a card into an ATM. To model this, we introduce a real-time aspect to negotiations. In our model of local-timed negotiations, agents have local reference times that evolve independently. Inspired by the model of networks of timed automata, each agent is equipped with a set of local clocks. Similar to timed automata, the outcomes of a negotiation contain guards and resets over the local clocks. As a new feature, we allow some interactions to force the reference clocks of the participating agents to synchronize. This synchronization constraint allows us to model interesting scenarios. Surprisingly, it also gives unlimited computing power. We show that reachability is undecidable for local-timed negotiations with a mixture of synchronized and unsynchronized interactions. We study restrictions on the use of synchronized interactions that make the problem decidable.Comment: A shorter version appears in FORMATS 202

Practical Distributed Control Synthesis

Classic distributed control problems have an interesting dichotomy: they are either trivial or undecidable. If we allow the controllers to fully synchronize, then synthesis is trivial. In this case, controllers can effectively act as a single controller with complete information, resulting in a trivial control problem. But when we eliminate communication and restrict the supervisors to locally available information, the problem becomes undecidable. In this paper we argue in favor of a middle way. Communication is, in most applications, expensive, and should hence be minimized. We therefore study a solution that tries to communicate only scarcely and, while allowing communication in order to make joint decision, favors local decisions over joint decisions that require communication.Comment: In Proceedings INFINITY 2011, arXiv:1111.267

Petri net controllers for Generalized Mutual Exclusion Constraints with floor operators

In this paper a special type of nonlinear marking specifications called stair generalized mutual exclusion constraints (stair-GMECs) is defined. A stair-GMEC can be represented by an inequality whose left-hand is a linear combination of floor functions. Stair-GMECs have higher modeling power than classical GMECs and can model legal marking sets that cannot be defined by OR–AND GMECs. We propose two algorithms to enforce a stair-GMEC as a closed-loop net, in which the control structure is composed by a residue counter, remainder counters, and duplicate transitions. We also show that the proposed control structure is maximally permissive since it prevents all and only the illegal trajectories of a plant net. This approach can be applied to both bounded and unbounded nets. Several examples are proposed to illustrate the approach

Formal Object Interaction Language: Modeling and Verification of Sequential and Concurrent Object-Oriented Software

As software systems become larger and more complex, developers require the ability to model abstract concepts while ensuring consistency across the entire project. The internet has changed the nature of software by increasing the desire for software deployment across multiple distributed platforms. Finally, increased dependence on technology requires assurance that designed software will perform its intended function. This thesis introduces the Formal Object Interaction Language (FOIL). FOIL is a new object-oriented modeling language specifically designed to address the cumulative shortcomings of existing modeling techniques. FOIL graphically displays software structure, sequential and concurrent behavior, process, and interaction in a simple unified notation, and has an algebraic representation based on a derivative of the π-calculus. The thesis documents the technique in which FOIL software models can be mathematically verified to anticipate deadlocks, ensure consistency, and determine object state reachability. Scalability is offered through the concept of behavioral inheritance; and, FOIL’s inherent support for modeling concurrent behavior and all known workflow patterns is demonstrated. The concepts of process achievability, process complete achievability, and process determinism are introduced with an algorithm for simulating the execution of a FOIL object model using a FOIL process model. Finally, a technique for using a FOIL process model as a constraint on FOIL object system execution is offered as a method to ensure that object-oriented systems modeled in FOIL will complete their processes based activities. FOIL’s capabilities are compared and contrasted with an extensive array of current software modeling techniques. FOIL is ideally suited for data-aware, behavior based systems such as interactive or process management software

Replicated ambient Petri nets

Recently we have introduced Ambient Petri nets, as a multilevel extension of the Elementary Object Systems, that can be used to model the concept of nested ambients from the Ambient Calculus. Both mobile computing and mobile computation are supported by that calculus, and then by means of our Ambient Petri nets we get a way to introduce in the world of Petri nets these important features of nowadays computing. Nevertheless, our basic proposal does not yet provide the suitable background for the modeling of replication, one of the basic operators from the original calculus, by means of which infinite processes are introduced and treated in a very simple way. In this paper we enrich our framework by introducing that operator. We obtain a simple and nice model in which the basic nets are still static and finite, since the dynamics of the systems can be covered by the adequate notion of marking, where all the copies generated by the application of the replication operator will live together, without interfering in an inadequate way