Resource-Constrained Workflow Nets Research Articles

Model checking Petri nets with names using data-centric dynamic systems

Abstract Petri nets with name creation and management ( ν -PNs) have been recently introduced as an expressive model for dynamic (distributed) systems, whose dynamics are determined not only by how tokens flow in the system, but also by the pure names they carry. On the one hand, this extension makes the resulting nets strictly more expressive than P/T nets: they can be exploited to capture a plethora of interesting systems, such as distributed systems enriched with channels and name passing, service interaction with correlation mechanisms, and resource-constrained workflow nets that explicitly account for process instances. On the other hand, fundamental properties like coverability, termination and boundedness are decidable for ν -PNs. In this work, we go one step beyond the verification of such general properties, and provide decidability and undecidability results of model checking ν -PNs against variants of first-order μ -calculus, recently proposed in the area of data-aware process analysis. While this model checking problem is undecidable in the general case, decidability can be obtained by considering different forms of boundedness, which still give raise to an infinite-state transition system. We then ground our framework to tackle the problem of soundness checking over workflow nets enriched with explicit process instances and resources. Notably, our decidability results are obtained via a translation to data-centric dynamic systems, a recently devised framework for the formal specification and verification of data-aware business processes working over full-fledged relational databases with constraints. In this light, our results contribute to the cross-fertilization between the area of formal methods for concurrent systems and that of foundations of data-aware processes, which has not been extensively investigated so far.

Resource Relocation in Workflow Nets With Time, Resource, and Task Priority Constraints

Complex workflows arising from practical applications usually combine time, resource, and task priority constraints. The goal of this paper is to formulate a suitable WF net model with all these three types of constraints, and to investigate the soundness property of the resulting model. Thus, the concept of a multilevel resource constrained workflow net (mlRCWF net) as being a place composition of resource constrained workflow (RCWF) nets is introduced, and its soundness property is investigated. This model is then enriched with time and task priority constraints. It is shown that the soundness property of timed priority mlRCWF nets can be reduced in linear time to the soundness property of (untimed) priority RCWF nets. A resource relocation policy is a policy by which resources already allocated to some task are then relocated to urgent tasks, the current task being thus delayed. When the current tasks support an indefinite delay, the soundness of timed priority mlRCWF nets with resource relocation can be reduced in quadratic time to the soundness property of (untimed) priority RCWF nets.

Safety and Soundness for Priced Resource-Constrained Workflow Nets

We extend workflow Petri nets wf-nets with discrete prices, by associating a price to the execution of a transition and to the storage of tokens. We first define the safety and the soundness problems for priced wf-nets. A priced wf-net is safe if no execution costs more than a given budget. The soundness problem is that of deciding whether the workflow can always terminate properly, where in the priced setting “properly” also means that the execution does not cost more than a given threshold. Then, we study safety and soundness of resource-constrained workflow nets rcwf-nets, an extension of wf-nets for the modeling of concurrent executions of a workflow, sharing some global resources. We develop a framework in which to study safety and soundness for priced rcwf-nets, that is parametric on the cost model. Then, that framework is instantiated, obtaining the cases in which the sum, the maximum, the average and the discounted sum of the prices of all instances are considered. We study the decidability and the complexity of these properties, together with their relation.

Controllable Deadlocks in Parallel Resource-Constrained Workflows

We study the verification of the soundness property for workflow nets extended with resources. A workflow is sound if it terminates properly (no deadlocks and livelocks are possible). A class of resource-constrained workflow nets (RCWF-nets) is considered, where resources can be used by a process instance, but cannot be created or spent. Two sound RCWF-nets using the same set of resources can be put in parallel. This parallel composition may in some cases produce additional deadlocks. A problem of deadlock avoidance in parallel workflows is studied, some methods of deadlock search and control are presented.

Soundness for Resource-Constrained Workflow Nets Is Decidable

We investigate the verification of the soundness property for workflow nets (WF-nets) extended with resources, thereby considering the most general instance of soundness, which requires that, for any number of instances, the WF-net has always the possibility to terminate, for a certain initial (finite) number of resource items per resource type; moreover, adding additional resources to a sound net does not violate the result. We prove that this problem is decidable by reducing it to a home-space problem, and we show how soundness can be decided by using the procedure for deciding a home-space property.

Decidability Results for Soundness Criteria of Resource-Constrained Workflow Nets

This paper focuses on the decidability status of various forms of behavioral correctness criteria for resource-constrained workflow (RCWF) nets (Petri net models of RCWF systems). These behavioral correctness criteria, usually called soundness criteria, are natural extensions of similar correctness criteria for workflow nets (Petri net models of workflow systems). While all forms of soundness are known to be decidable for workflow nets, only soundness for RCWF nets with just one resource type is known to be decidable. In this paper, we show that if we limit the number of cases, then soundness for RCWF nets with arbitrarily many resource types is decidable. Moreover, we show that some “intermediate” forms of soundness, as well as a restrictive form of structural soundness for RCWF nets, are decidable too. The proof technique is based on instantiation nets as a general tool for dealing with arbitrarily many cases and arbitrarily large resources in workflow nets and RCWF nets. It is also shown why this technique cannot be extended to the most general form of soundness.