A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)

Meeting abstrac

caller

FIFO channel systems, in which messages between processes are cached in queues, are fundamental to the modeling of concurrency. A great deal of effort has gone into identifying scenarios where reasoning about such systems is decidable, often through establishing that the language of all channel contents is regular. Most prior results in this area focus on the effect of repetitions of individual operations sequences or they constrain the channels either to be lossy or to be polynomially bounded (that is, the number of words of a given length describing channel contents is bounded by a polynomial). We focus on piecewise languages for both describing operations and channel contents. Piecewise languages restrict the Kleene star operation to be applied to sets of letters only. For example, a(b+c) ∗ is piecewise (but not polynomially bounded). These languages correspond to the Σ2 class of the first-order quantifier hierarchy. It is already known that piecewiseness plays a key role in establishing regularity results about parameterized systems subjected to rewritings according to semicommutation rules. In this paper, we show that piecewiseness is central to the understanding of FIFO channel systems. Our contribution is to study the effect of iterating sets of operations, while extending and unifying previous work on both lossy and perfect FIFO systems. In particular, we show that well-quasi-orderings are important to Σ2, not only to the lossy systems of Π1. Moreover, we show that Σ2 also describes limits in a class of FIFO systems that include iterations of arbitrary sets of simultaneous read and write operations

Loop Freedom in AODVv2

Part 2: Formal Models of Concurrent and Distributed SystemsInternational audienceThe AODV protocol is used to establish routes in a mobile, ad-hoc network (MANET). The protocol must operate in an adversarial environment where network connections and nodes can be added or removed at any point. While the ability to establish routes is best-effort under these conditions, the protocol is required to ensure that no routing loops are ever formed. AODVv2 is currently under development at the IETF, we focus attention on version 04. We detail two scenarios that show how routing loops may form in AODVv2 routing tables. The second scenario demonstrates a problem with the route table update performed on a Broken route entry. Our solution to this problem has been incorporated by the protocol designers into AODVv2, version 05. With the fix in place, we present an inductive and compositional proof showing that the corrected core protocol is loop-free for all valid configurations

Piecewise FIFO Channels Are Analyzable

Abstract. FIFO systems consisting of several components that communicate via unbounded perfect FIFO channels arise naturally in modeling distributed systems. Despite well-known difficulties in analyzing such systems, they are of significant interest as they can describe a wide range of Internet-based communication protocols. Previous work has shown that the piecewise languages play important roles in the study of FIFO systems. In this paper, we show that FIFO systems composed of piecewise components can in fact be analyzed algorithmically. We demonstrate that any FIFO system composed of piecewise components can be described by a finite state, abridged structure, representing an expressive abstraction of the system. We present a procedure for building the abridged model and prove that this procedure terminates. We show that we can analyze the infinite computations of the more concrete model by analyzing the computations of the finite, abridged model. This enables us to check properties of the FIFO systems including safety properties of the components as well as a general class of end-to-end system properties. Finally, we apply our analysis method to an IP-telecommunication architecture to demonstrate the utility of our approach.

Model Checking Real-Time Properties of Symmetric Systems

We develop efficient algorithms for model checking quantitative properties of symmetric reactive systems in the general framework of a Real-Time Mu-calculus. Previous work has been limited to qualitative correctness properties. Our work not only permits handling of quantitative correctness, but it provides a strictly more expressive framework for qualitative correctness since the Mu-calculus strictly subsumes, e.g, CTL*. Unlike the previous "group-theoretic" approaches of [CE96] and [ES96] and the technical "automata-theoretic" approach of [ES97], our new approach may be viewed as "model-theoretic"