Oi Olivia Oanea

Nested nets for adaptive systems

We consider nested nets, i.e. Petri nets in which tokens can be Petri nets themselves. We study the value semantics of nested nets rather than the reference semantics, and apply nested nets to model adaptive workflow, i.e. flexible workflow that can be modified during the execution. A typical domain with a great need for this kind of workflow is health care, from which domain we choose the running example. To achieve the desired flexibility we allow transitions that create new nets out of the existing ones. Therefore, nets with completely new structure can be created at the run time. We show that by careful selection of basic operations on the nets we can obtain a powerful modeling formalism that enforces correctness of models. Moreover, the formalism can be implemented based on existing workflow engines.

Yasper: a tool for workflow modeling and analysis

This paper presents Yasper, a tool for modeling, analyzing and simulating workflow systems, based on Petri nets. Yasper puts Petri net modeling in the hands of business analysts and software architecture designers. They can specify systems in familiar terms (XOR choice, workflow, cases, roles, processing time and cost), and can directly run manual and automatic simulations on the resulting models to analyze correctness and performance. Yasper was designed to cooperate with other tools, such as Petri net analyzers, and off-the-shelf software for data (color) handling and forms handling

Colored petri nets to verify extended event-driven process chains

Business processes are becoming more and more complex and at the same time their correctness is becoming a critical issue: The costs of errors in business information systems are growing due to the growing scale of their application and the growing degree of automation. In this paper we consider Extended Event-driven Process Chains (eEPCs), a language which is widely used for modeling business processes, documenting industrial reference models and designing workflows. We describe how to translate eEPCs into timed colored Petri nets in order to verify processes given by eEPCs with the CPN Tools.

New algorithms for deciding the siphon-trap property

The siphon-trap property, also known as Commoner-Hack property, establishes a relation between structural entities within a Petri net – the eponymous siphons and traps. The property is linked to the behavior of a Petri net, for instance to deadlock freedom and liveness of the net. It is nevertheless nontrivial to decide the property as a net can have exponentially many siphons and traps even if only minimal siphons are considered. Consequently, the value of the property depends on the availability of powerful decision procedures. We contribute to this issue by proposing two new methods for deciding the siphon-trap property. One is a plain translation of the property into a Boolean satisfiability (SAT) problem, which exploits the fact that incredibly powerful SAT solvers are available. The second procedure has a divide-and-conquer nature which builds upon a decomposition of a Petri net into open nets and projects information about siphons and traps onto the interfaces of the components.

Verifying generalized soundness of workflow nets

We improve the decision procedure from [10] for the problem of generalized soundness of workflow nets. A workflow net is generalized sound iff every marking reachable from an initial marking with k tokens on the initial place terminates properly, i.e. it can reach a marking with k tokens on the final place, for an arbitrary natural number k. Our new decision procedure not only reports whether the net is sound or not, but also returns a counterexample in case the workflow net is not generalized sound. We report on experimental results obtained with the prototype we made and explain how the procedure can be used for the compositional verification of large workflows.

LogLogics: A logic for history-dependent business processes

Choices in business processes are often based on the process history saved as a log-file listing events and their time stamps. In this paper we introduce LogLogics, a finite-path variant of the Timed Propositional Temporal Logic with Past, which can be in particular used for specifying guards in business process models. The novelty is due to the presence of boundary points corresponding to the starting and current observation points, which gives rise to a three-valued logic allowing us to distinguish between temporal formulas that hold for any log extended with some possible past and future (true), those that do not hold for any extended log (false) and those that hold for some but not all extended logs (unknown). We reduce the check of the truth value of a LogLogics formula to a check on a finite abstraction and present an evaluation algorithm. We also define LogLogics patterns for commonly occurring properties.

History-based joins: semantics, soundness and implementation

In this paper we study the use of case history for control structures in workflow processes. In particular we introduce a history-dependent join. History dependent control offers much more modeling power than classical control structures and it solves several semantical problems of industrial modeling frameworks. We study the modeling power by means of workflow patterns. Since proper completion (i.e. the ability of any configuration reachable from the initial one to reach the final one) is always an important ”sanity check” of process modeling, we introduce a modeling method that guarantees this property for the new control structures. Finally we consider an implementation of the proposed control structures on top of an existing workflow engine.