Our main goal is automating termination proofs for programs in rewriting-based languages with features such as: (i) expressive type structures, (ii) conditional rules, (iii) matching modulo axioms, and (iv) contextsensitive rewriting. Specifically, we present a new operational termination method for membership equational programs with features (i)-(iv) that can be applied to programs in membership equational logic (MEL). The method first transforms a MEL program into a simpler, yet semantically equivalent, conditional order-sorted (OS) program. Subsequent trasformations make the OS-program unconditonal, and, finally, unsorted. In particular, we extend and generalize to this richer setting an order-sorted termination technique for unconditional OS programs proposed by Ölveczky and Lysne. An important advantage of our method is that it minimizes the use of conditional rules and produces simpler transformed programs whose termination is often easier to prove automatically.

Despite the remarkable development of the theory of termination of rewriting, its application to high-level programming languages is far from being optimal. This is due to the need for features such as conditional equations and rules, types and subtypes, (possibly programmable) strategies for controlling the execution,

Termination of context-sensitive rewriting (CSR) is an interesting problem with several applications in the fields of term rewriting and in the analysis of programming languages like CafeOBJ, Maude, OBJ, etc. The dependency pair approach, one of the most powerful techniques for proving termination of rewriting, has been adapted to be used for proving termination of CSR. The corresponding notion of contextsensitive dependency pair (CSDP) is different from the standard one in that collapsing pairs (i.e., rules whose right-hand side is a variable) are considered. Although the implementation and practical use of CSDPs lead to a powerful framework for proving termination of CSR, handling collapsing pairs is not easy and often leads to impose heavy requirements over the base orderings which are used to achieve the proofs. A recent proposal removes collapsing pairs by transforming them into sets of new (standard) pairs. In this way, though, the role of collapsing pairs for modeling context-sensitive computations gets lost. This leads to a less intuitive and accurate description of the termination behavior of the system. In this paper, we show how to get the best of the two approaches, thus obtaining a powerful context-sensitive dependency pair framework which satisfies all practical and theoretical expectations.

Abstract. Rewriting logic is a flexible and general logic to specify concurrent systems. To prove properties about concurrent systems in temporal logic, it is very useful to use simulations that relate the transitions and atomic predicates of a system to those of a potentially much simpler one; then, if the simpler system satisfies a property ϕ in a suitable temporal logic we are guaranteed that the more complex system does too. In this paper, the suitability of rewriting logic as a formal framework not only to specify concurrent systems but also to specify simulations is explored in depth. For this, increasingly more general notions of simulation (allowing stuttering) are first defined for Kripke structures, and suitable temporal logics allowing properties to be reflected back by such simulations are characterized. The paper then proves various representability results à la Bergstra and Tucker, showing that recursive Kripke structures and recursive simulation maps (resp. r.e. simulation relations) can always be specified in a finitary way in rewriting logic. Using simulations typically requires both model checking and theorem proving, since their correctness requires discharging proof obligations. In this regard, rewriting logic, by containing equational logic as a sublogic and having equationally-based inductive theorem proving at its disposal, is shown to be particularly well-suited for verifying the correctness of simulations.

Orc is a language for orchestration of web services developed by J. Misra that offers simple, yet powerful and elegant, constructs to succinctly program sophisticated web orchestration applications. However, because of its real-time nature and the different priorities given to internal and external events in an Orc program, giving a formal operational semantics that captures the real-time behavior of Orc programs is nontrivial and poses some interesting challenges. In this report, we first propose a realtime operational Orc semantics, that captures the informal operational semantics given in [26]. This operational semantics is given as a rewrite theory R sos Orc in which the elapse of time is explicitly modeled. This is followed by presenting a much more efficient reduction semantics of Orc, which is provably equivalent to the SOS semantics. A detailed proof of strong bisimilarity of the two semantic specifications is then given. In both

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AADL (Architectural Analysis and Design Language) is a textual and graphical language used to design and analyze software architecture of embedded real time systems. Many tools and models provide semantics and precise meaning for AADL architecture behavior. However, they are not supported by a well defined formal semantics. This paper suggets Rewriting Logic via its practical language Maude as an adequate formalism for modeling behavior concepts in an AADL architectural description. Besides, RT-Maude system offers a natural support to execute and prototype real-time object-oriented modules formalizing AADL architecture behavior composed of several communicating threads.

Abstract. We present a novel approach based on inductive theorem proving for verifying invariants of dynamic systems specified in rewriting logic, a formal specification language implemented in the Maude system. An invariant is a property that holds on all the states that are reachable from a given class of initial states. Our approach consists in encoding the semantic aspects that are relevant for our task (namely, verifying invariance properties of the specified systems) in membership equational logic, a sublogic of rewriting logic. The invariance properties are then formalized over the encoded rewrite theories and are proved using an inductive theorem prover for membership equational logic also implemented in the Maude system using its reflective capabilities. We illustrate our approach by verifying mutual exclusion properties of a readers-writers system and of an n-process version of the Bakery algorithm. 1

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Abstract. Rule-based programming has been shown to be very successful in many application areas. Two prominent examples are the specification of model transformations in model driven development approaches and the definition of structured operational semantics of formal languages. General rewriting frameworks such as Maude are flexible enough to allow the programmer to adopt and mix various rule styles. The choice between styles can be biased by the programmer’s background. For instance, experts in visual formalisms might prefer graph-rewriting styles, while experts in semantics might prefer structurally inductive rules. This paper evaluates the performance of different rule styles on a significant benchmark taken from the literature on model transformation. Depending on the actual transformation being carried out, our results show that different rule styles can offer drastically different performances. We point out the situations from which each rule style benefits to offer a valuable set of hints for choosing one style over the other. 1