A distributed spanning tree algorithm for topology-aware networks

Abstract. A topology-aware network is a dynamic network in which the nodes can detect whether locally topology changes occur. Many modern networks, like IEEE 1394.1, are topology-aware networks. We present a distributed algorithm for computing and maintaining an arbitrary spanning tree in such a topology-aware network. Although usually minimal spanning trees are studied, in practice arbitrary spanning trees are often sufficient. Since our algorithm is not involved in the detection of topology changes, it performs better than the spanning tree algorithms in standards like IEEE 802.1. Because reasoning about distributed algorithms is rather tricky, we use a systematic approach to prove our algorithm

Abstraction in parameterised Boolean equation systems

We present a general theory of abstraction for a variety of verification problems. Our theory is set in the framework of parameterized Boolean equation systems. The power of our abstraction theory is compared to that of generalised Kripke modal transition systems (GTSs). We show that for model checking the modal µ-calculus, our abstractions can be exponentially more succinct than GTSs and our theory is as complete as the GTS framework for abstraction. Furthermore, we investigate the completeness of our theory for verification problems other than the modal µ-calculus. We illustrate the potential of our theory through case studies using the first-order modal µ-calculus and a real-time extension thereof, conducted using a prototype implementation of a new syntactic transformation for equation systems

Generic programming in the mCRL2 toolset

The mCRL2 tool set [GKM+08] is a tool set for verification and validation of concurrent processes, based on process algebra speci??cations. The mCRL2 language is based on the Algebra of Communicating Processes (ACP), which is extended to include data and time. This paper reports on experiences with generic programming in C++ as applied in the implementation of the tool set. C++ concepts, a type system for templates [RS06], form a key ingredient of this style of programming. Using concept definitions, requirements on template types can be defined that are type checked during compile time. The main benefits for the mCRL2 tool set are uniform and exible interfaces that operate on well-defined types, and a signi??cant increase in code reuse. The use of concepts also promotes the writing of code that corresponds closely to pseudo code, since the chosen concepts correspond naturally with domain specific concepts. This will be illustrated by a simple use case, namely substitution functions. Generic programming is about generalizing software components, to enable reuse in a wide variety of situations. In C++, generic programming is enabled using templates. C++ concepts are proposed as a means to type check template types. A concept is a set of requirements (valid expressions, associated types, semantic invariants, complexity guarantees, and so on) that a type must fulfill to be correctly used as an argument in a call to a generic algorithm, see [RS06]. Language support for concepts has been proposed [GJS+06] for the next version of the C++ standard, C++0x. Concepts will be used to make the specification of the C++ standard library more complete and precise. A derivative of the GNU C++ compiler [Gre08] already implements language support for concepts. In the mCRL2 tool set we have used a portable library for concept checking. Most uses of generic programming in general, and more specifically the use of concepts, that are described in the literature treat the construction of data structures and algorithms that operate on these, see e.g. [GL05]

Experience in developing the mCRL2 toolset

mCRL2 is a language with a toolset for formal analysis of behaviour of concurrent systems. It is developed in an academic research group to support process algebra based verification in an academic as well as an industrial setting. This paper provides an insight into the experiences and practises in developing and maintaining the mCRL2 toolset

Physicians' and nurses' opinions on selective decontamination of the digestive tract and selective oropharyngeal decontamination: a survey

Contains fulltext : 89741.pdf (publisher's version ) (Open Access)INTRODUCTION: Use of selective decontamination of the digestive tract (SDD) and selective oropharyngeal decontamination (SOD) in intensive care patients has been controversial for years. Through regular questionnaires we determined expectations concerning SDD (effectiveness) and experience with SDD and SOD (workload and patient friendliness), as perceived by nurses and physicians. METHODS: A survey was embedded in a group-randomized, controlled, cross-over multicenter study in the Netherlands in which, during three 6-month periods, SDD, SOD or standard care was used in random order. At the end of each study period, all nurses and physicians from participating intensive care units received study questionnaires. RESULTS: In all, 1024 (71%) of 1450 questionnaires were returned by nurses and 253 (82%) of 307 by physicians. Expectations that SDD improved patient outcome increased from 71% and 77% of respondents after the first two study periods to 82% at the end of the study (P = 0.004), with comparable trends among nurses and physicians. Nurses considered SDD to impose a higher workload (median 5.0, on a scale from 1 (low) to 10 (high)) than SOD (median 4.0) and standard care (median 2.0). Both SDD and SOD were considered less patient friendly than standard care (medians 4.0, 4.0 and 6.0, respectively). According to physicians, SDD had a higher workload (median 5.5) than SOD (median 5.0), which in turn was higher than standard care (median 2.5). Furthermore, physicians graded patient friendliness of standard care (median 8.0) higher than that of SDD and SOD (both median 6.0). CONCLUSIONS: Although perceived effectiveness of SDD increased as the trial proceeded, both among physicians and nurses, SOD and SDD were, as compared to standard care, considered to increase workload and to reduce patient friendliness. Therefore, education about the importance of oral care and on the effects of SDD and SOD on patient outcomes will be important when implementing these strategies. TRIAL REGISTRATION: ISRCTN35176830