Search

A general theory introducing asymptotic complexity to testing is presented. Our goal is measuring how fast the effort of testing must increase to reach higher levels of partial certainty on the correctness of the implementation under test (IUT). By recent works it is known that, for many practical testing scenarios, any partial level of correctness certainty less than 1 (where 1 means full certainty) can be reached by some finite test suite. In this paper we address the problem of finding out how fast must these test suites grow as long as the target level gets closer to 1. More precisely, we want to study how test suites grow with α, where α is the inverse of the distance to 1 (e.g., if α = 4 then our target level is 0.75 = 1 − 1 4 ). A general theory to measure this testing complexity is developed. We use this theory to analyze the testing complexity of some general testing problems, as well as the complexity of some specific testing strategies for these problems, and discover that they are within e.g., O ( l o g α ) , O ( l o g 2 α ) , O ( α ) , O ( α l o g α ) , or O ( α ) . Similarly as the computational complexity theory conceptually distinguishes between the complexity of problems and algorithms, tightly identifying the complexity of a testing problem will require reasoning about any testing strategy for the problem. The capability to identify testing complexities will provide testers with a measure of the productivity of testing, that is, a measure of the utility of applying the ( n + 1 ) -th planned test case (after having passed the n previous ones) in terms of how closer would that additional test case get us to the (ideal) complete certainty on the IUT (in-)correctness.

We combine two of the existing approaches to the study of concurrency by means of multiset rewriting: multiset rewriting with existential quantification (MSR) and constrained multiset rewriting. We obtain ν-MSR, where we rewrite multisets of atomic formulae, in which terms can only be pure names, where some names can be restricted. We consider the subclass of depth-bounded ν-MSR, for which the interdependence of names is bounded. We prove that they are strictly Well Structured Transition Systems, so that coverability, termination and boundedness are all decidable for depth-bounded ν-MSR. This allows us to obtain new verification results for several formalisms with name binding that can be encoded within ν-MSR, namely polyadic ν-PN (Petri nets with tuples of names as tokens), the π-calculus, MSR or Mobile Ambients.

Pure names are identifiers with no relation between them, except equality and inequality. In previous works we have extended P/T nets with the capability of creating and managing pure names, obtaining ν-PNs and proved that they are strictly well structured (WSTS), so that coverability and boundedness are decidable. Here we use the framework recently developed by Finkel and Goubault-Larrecq for forward analysis for WSTS, in the case of ν-PNs, to compute the cover, that gives a good over approximation of the set of reachable markings. We prove that the least complete domain containing the set of markings is effectively representable. Moreover, we prove that in the completion we can compute least upper bounds of simple loops. Therefore, a forward Karp-Miller procedure that computes the cover is applicable. However, we prove that in general the cover is not computable, so that the procedure is non-terminating in general. As a corollary, we obtain the analogous result for Transfer Data nets and Data Nets. Finally, we show that a slight modification of the forward analysis yields decidability of a weak form of boundedness called width-boundedness, and identify a subclass of ν-PN that we call dw-bounded ν-PN, for which the cover is computable.

In this paper we study decidability of several extensions of P/T nets with name creation and/or replication. In particular, we study how to restrict the models of RN systems (P/T nets extended with replication, for which reachability is undecidable) and ν-RN systems (RN extended with name creation, which are Turing-complete, so that coverability is undecidable), in order to obtain decidability of reachability and coverability, respectively. We prove that if we forbid synchronizations between the different components in a RN system, then reachability is still decidable. Similarly, if we forbid name communication between the different components in a ν-RN system, or restrict communication so that it is allowed only for a given finite set of names, we obtain decidability of coverability. Finally, we consider a polyadic version of ν-PN (P/T nets extended with name creation), that we call pν-PN, in which tokens are tuples of names. We prove that pν-PN are Turing complete, and discuss how the results obtained for ν-RN systems can be translated to them.

Mobile Synchronizing Petri Nets (MSPN's) are a model for mobility and coordination based on coloured Petri Nets, in which systems are composed of a collection of (possibly mobile) hardware devices and mobile agents, both modelled homogenously. In this paper we approach their verification, for which we have chosen to code MSPN's into rewriting logic. In order to obtain a representation of MSPN systems by means of a rewrite theory, we develop a class of them, that we call ν-Abstract Petri nets (ν-APN's), which are easily representable in that framework. Moreover, the obtained representation provides a local mechanism for fresh name generation. Then we prove that, even if ν-APN's are a particular class of MSPN systems, they are strong enough to capture the behaviour of any MSPN system. We have chosen Maude to implement ν-APN's, as well as the translation from MSPN's to ν-APN's, for which we make intensive use of its reflective features.

Asynchronous event-driven programming has become a central model for building responsive and efficient software systems, from low-level kernel modules, device drivers, and embedded systems, to consumer application on platforms such as .Net, Android, iOS, as well as in the web browser. Being fundamentally concurrent, such systems are vulnerable to subtle and elusive programming errors which, in principle, could be systematically discovered with automated techniques such as model checking. However, current development of such automated techniques are based on formal models which make great simplifications in the name of analysis decidability: they ignore event-based synchronization, and they assume concurrent tasks execute serially. These simplifications can ultimately lead to false positives, in reporting errors which are infeasible considering event-based synchronization, as well as false negatives, overlooking errors which arise due to interaction between concurrent tasks.

We study dynamic networks of infinite-state timed processes, modelled as unbounded Petri nets. These processes can evolve autono-mously, synchronize with each other (e.g., in order to gain access to some shared resources) and be created or become garbage dynamically. We introduce dense time in two different ways. First, we consider that each token in each process carries a real valued clock. We prove that this model can faithfully simulate Turing-complete formalisms and, in particular, safety properties are undecidable for them. Second, we consider locally-timed processes, where each process carries a single real valued clock. For them, we prove decidability of safety properties by a non-trivial instantiation of the framework of Well-Structured Transition Systems.

We study dynamic networks of infinite-state timed processes, where each process is a Petri net carrying a single real valued clock. We compare their expressiveness with other models within the class of Well-Structured Transition Systems, using coverability languages. We prove that unbounded places are a strict resource, meaning that extra unbounded places provides strictly with extra expressiveness. Also, we prove that if no unbounded places are allowed, then the obtained model is equivalent to Timed Petri nets. We conclude that dynamic networks of Timed Petri Nets are strictly more expressive than Timed Petri Nets.

International audience; We characterize the importance of resources (like counters, channels, or alphabets) when measuring the expressiveness of Well-Structured Transition Systems (WSTS). We establish, for usual classes of well partial orders, the equivalence between the existence of order reflections (non-monotonic order embeddings) and the simulations with respect to coverability languages. We show that the non-existence of order reflections can be proved by the computation of order types. This allows us to extend the current classification of WSTS, in particular solving some open problems, and to unify the existing proofs.

To the best of our knowledge, we characterize for the first time the importance of resources (counters, channels, alphabets) when measuring expressiveness of WSTS. We establish, for usual classes of wpos, the equivalence between the existence of order reflections (nonmonotonic order embeddings) and the simulations with respect to coverability languages. We show that the non-existence of order reflections can be proved by the computation of order types. This allows us to solve some open problems and to unify the existing proofs of the WSTS classification.

Pure names are identifiers with no relation between them, except equality and inequality. In previous works we have extended P/T nets with the capability of creating and managing pure names, obtaining ν-APNs and proved that they are strictly well structured (WSTS), so that coverability and boundedness are decidable. Here we use the framework recently developed by Finkel and Goubault-Larrecq for forward analysis for WSTS, in the case of ν-APNs, to compute the cover, that gives a good over approximation of the set of reachable markings. We prove that the least complete domain containing the set of markings is effectively representable. Moreover, we prove that in the completion we can compute least upper bounds of simple loops. Therefore, a forward Karp-Miller procedure that computes the cover is applicable. However, we prove that in general the cover is not computable, so that the procedure is non-terminating in general. As a corollary, we obtain the analogous result for Transfer Data nets and Data Nets. Finally, we show that a slight modification of the forward analysis yields decidability of a weak form of boundedness called width-boundedness.

We apply language theory to compare the expressive power of models that extend Petri nets with features like colored tokens and/or whole place operations. Specifically, we consider extensions of Petri nets with transfer and reset operations defined for black indistinguishable tokens (Affine Well-Structured Nets), extensions in which tokens carry pure names dynamically generated with special ν-transitions (ν-APN), and extensions in which tokens carry data taken from a linearly ordered domain (Data nets and CMRS). These models are well-structured transitions systems. In order to compare these models we consider the families of languages they recognize, using coverability as accepting condition. With this criterion, we prove that ν-APNs are in between AWNs and Data Nets/CMRS. Moreover, we prove that the family of languages recognized by ν-APNs satisfies a good number of closure properties, being a semi-full AFL. These results extend the currently known classification of the expressive power of well-structured transition systems with new closure properties and new relations between extensions of Petri nets.

In previous works we defined *** -APNs, an extension of P/T nets with the capability of creating and managing pure names. We proved that, though reachability is undecidable, coverability remains decidable for them. We also extended P/T nets with the capability of nets to replicate themselves, creating a new component, initially marked in some fixed way, obtaining g-RN systems. We proved that these two extensions of P/T nets are equivalent, so that g-RN systems have undecidable reachability and decidable coverability. Finally, for the class of the so called *** -RN systems, P/T nets with both name creation and replication, we proved that they are Turing complete, so that also coverability turns out to be undecidable. In this paper we study how can we restrict the models of *** -APNs (and, therefore, g-RN systems) and *** -RN systems in order to keep decidability of reachability and coverability, respectively. We prove that if we forbid synchronizations between the different components in a g-RN system, then reachability is still decidable. The proof is done by reducing it to reachability in a class of multiset rewriting systems, similar to Recursive Petri Nets. Analogously, if we forbid name communication between the different components in a *** -RN system, or restrict communication to happen only for a given finite set of names, we obtain decidability of coverability.

Bisimulation semantics are a very pleasant way to define the semantics of systems, mainly because the simplicity of their definitions and their nice coalgebraic properties. However, they also have some disadvantages: they are based on a sequential operational semantics defined by means of an ordinary transition system, and in order to be bisimilar two systems have to be "too similar". In this work we will present several natural proposals to define weaker bisimulation semantics that we think properly capture the desired behaviour of distributed systems. The main virtue of all these semantics is that they are real bisimulation semantics, thus inheriting most of the good properties of bisimulation semantics. This is so because they can be defined as particular instances of Jacobs and Hughes' categorical definition of simulation, which they have already proved to satisfy all those properties.

In this paper we extend our basic model of Ubiquitous Nets, by adding a replication operator that creates new copies of the net firing the replicating transition. We prove that the location attribute and thus the mobility feature are not essential characteristics of the obtained model, since it is equivalent to the particular case of Centralized Systems, where all components are stationary and co-located in a single location. This allows us to restrict ourselves to Centralized Systems when studying the decidability of reachability and coverability properties. In this way, we prove that both reachability and coverability remain decidable. Finally, we introduce an alternative version that includes a garbage collection mechanism that allows us to remove empty nets from the state of the system. We show that in this case coverability remains decidable.

Several years before the popularization of the Internet, Mark Weiser proposed the concept of ubiquitous computing with the purpose of enhancing the use of computers by making many computers available throughout the physical environment, but making them effectively invisible to the user. Nowadays, such idea affects all areas of computing science, including both hardware and software. In this paper, a formal model for ubiquitous systems based on Petri nets is introduced and motivated with examples and applications. This simple model allows the definition of two-level ubiquitous systems, composed of a collection of processor nets providing services, and a collection of process nets requesting those services. The modeled systems abstract from middleware details, such as service discovery protocols, and security infrastructures, such as PKI’s or trust policies, but not from mobility or component compatibility.