Lending Petri nets and contracts

Choreography-based approaches to service composition typically assume that, after a set of services has been found which correctly play the roles prescribed by the choreography, each service respects his role. Honest services are not protected against adversaries. We propose a model for contracts based on a extension of Petri nets, which allows services to protect themselves while still realizing the choreography. We relate this model with Propositional Contract Logic, by showing a translation of formulae into our Petri nets which preserves the logical notion of agreement, and allows for compositional verification

Maude: specification and programming in rewriting logic

Maude is a high-level language and a high-performance system supporting executable specification and declarative programming in rewriting logic. Since rewriting logic contains equational logic, Maude also supports equational specification and programming in its sublanguage of functional modules and theories. The underlying equational logic chosen for Maude is membership equational logic, that has sorts, subsorts, operator overloading, and partiality definable by membership and equality conditions. Rewriting logic is reflective, in the sense of being able to express its own metalevel at the object level. Reflection is systematically exploited in Maude endowing the language with powerful metaprogramming capabilities, including both user-definable module operations and declarative strategies to guide the deduction process. This paper explains and illustrates with examples the main concepts of Maude's language design, including its underlying logic, functional, system and object-oriented modules, as well as parameterized modules, theories, and views. We also explain how Maude supports reflection, metaprogramming and internal strategies. The paper outlines the principles underlying the Maude system implementation, including its semicompilation techniques. We conclude with some remarks about applications, work on a formal environment for Maude, and a mobile language extension of Maude

Combining theorem proving and narrowing for rewriting-logic specifications

International audienceWe present an approach for verifying dynamic systems specified in rewriting logic, a formal specification language implemented in the Maude system. Our approach is tailored for invariants, i.e., properties that hold on all states reachable from a given class of initial states. The approach consists in encoding invariance properties into inductive properties written in membership equational logic, a sublogic of rewriting logic also implemented in Maude. The invariants can then be verified using an inductive theorem prover available for membership equational logic, possibly in interaction with narrowing-based symbolic analysis tools for rewriting-logic specifications also available in the Maude environment. We show that it is possible, and useful, to automatically test invariants by symbolic analysis before interactively proving them

Proving Positive Almost-Sure Termination

Rapport interne.In order to extend the modeling capabilities of rewriting systems, it is rather natural to consider that the firing of rules can be subject to some probabilistic laws. Considering rewrite rules subject to probabilities leads to numerous questions about the underlying notions and results. We focus here on the problem of termination of a set of probabilistic rewrite rules. A probabilistic rewrite system is said almost surely terminating if the probability that a derivation leads to a normal form is one. Such a system is said positively almost surely terminating if furthermore the mean length of a derivation is finite. We provide several results and techniques in order to prove positive almost sure termination of a given set of probabilistic rewrite rules. All these techniques subsume classical ones for non-probabilistic systems

Generalized Rewrite Theories

Since its introduction, more than a decade ago, rewriting logic has attracted the interest of both theorists and practitioners, who have contributed in showing its generality as a semantic and logical framework and also as a programming paradigm. The experimentation conducted in these years has suggested that some significant extensions to the original definition of the logic would be very useful in practice. In particular, the Maude system now supports subsorting and conditions in the equational logic for data, and also frozen arguments to block undesired nested rewritings; moreover, it allows equality and membership assertions in rule conditions. In this paper, we give a detailed presentation of the inference rules, model theory, and completeness of such generalized rewrite theories

Streamlining Policy Creation in Policy Frameworks

{\it Policy frameworks} provide a technique for improving reuse in program analysis: the same language frontend, and a core analysis semantics, can be shared among multiple analysis policies for the same language, while analysis domains (such as units of measurement) can be shared among frameworks for different languages. One limitation of policy frameworks is that, in practice, adding a new policy can still require a significant level of knowledge about the internals of the semantics definition. This abstract describes work on extending policy frameworks to solve this limitation, making policies reflective over their requirements and generating the policy semantics from a higher-level policy description language

A generalized formal semantic framework for smart contracts

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A declarative debugger for Maude functional modules

AbstractA declarative debugger for Maude functional modules, which correspond to executable specifications in membership equational logic, is presented. Starting from an incorrect computation, declarative debugging builds a debugging tree as a logical representation of the computation, that then is traversed by asking questions to an external oracle until the error is found. We summarize the construction of appropriate debugging trees for oriented equational and membership inferences, where all the nodes whose correctness does not need any justification have been collapsed. The reflective features of Maude allow us to generate and navigate the debugging tree of a Maude computation using operations in Maude itself; even the user interface of the declarative debugger can be specified in this way. We present the debugger's main features, such as two different strategies to traverse the debugging tree, use of a correct module to reduce the number of questions asked to the user, selection of trusted vs. suspicious statements by means of labels, and trusting of statements “on the fly.