2012 Ninth International Conference on Quantitative Evaluation of Systems

Synthesis is the automated construction of a system from its specification. In standard temporal-synthesis algorithms, it is assumed the system is constructed from scratch. This, of course, rarely happens in real life. In real life, almost every non-trivial system, either in hardware or in software, relies heavily on using libraries of reusable components. Furthermore, other contexts, such as web-... View full abstract»

In this paper, we introduce the notion of decoupled speed scaling, wherein the speed scaling function is completely decoupled from the scheduling policy used in a simple single-server computer system. As an initial result, we first demonstrate that the Fair Sojourn Protocol (FSP) scheduling policy does not work properly with coupled (native) speed scaling, but that it can and does work well with d... View full abstract»

In this paper we show how program code and performance models can be made to cooperate seamlessly to support continuous software performance testing throughout the development lifecycle. We achieve this by extending our existing VEX tool for executing programs in virtual time so that events that occur during normal execution and those that occur during the simulation of a performance model can be ... View full abstract»

Consider a Markov modulated fluid queue with multiple layers separated by a finite number of boundaries, where each layer is characterized by its own set of matrices. In the past, matrix analytic methods have been devised to determine the stationary behavior of such a fluid queue for no-resistance, sticky and repellent boundaries. In this paper we extend this approach by allowing general phase tra... View full abstract»

A wide range of real life systems are modeled by queueing systems with finite capacity buffers. There are well established numerical procedures for the analysis of these queueing models when the load islower or higher than the system capacity, but these numerical methods become unstable as the loadgets close to the system capacity. We present simple modifications of the standard computational meth... View full abstract»

To deal with the problem of state space explosion in Markovian models often compositional modeling and the aggregation of components are used. Several approximate aggregation methods exist which are usually based on heuristics. This paper presents a new aggregation approach for Markovian components which computes aggregates that minimize the difference according to some algebraically defined funct... View full abstract»

We compare population models in terms of Continuous Time Markov Chains with embedded deterministic delays (delayed CTMC), in which an exponential timed transition can only update the state of the system after a deterministicdelay, and delay differential equations (DDE). We prove a fluid approximation theorem, showing that, when the size of the population goes to infinity, the delayed CTMC converge... View full abstract»

We extend the mean-field (a.k.a. fluid-analysis) approach for massively-parallel continuous-time Markov chains (CTMCs) to models with both Markovian and deterministically-timed transitions. We introduce a new low-level formalism for specifying massively-parallel models with generally-timed transitions, the population generalised semi-Markov process (PGSMP). We then show how systems of coupled dela... View full abstract»

We present a new symbolic approach for the steady-state solution of ergodic continuous-time Markov chains(CTMCs) using iterative methods, based on Edge-Valued Multi-way Decision Diagrams (EVMDDs) to store an indexing function for the structured states and the transition rate matrix. The approach is applicable to any structured CTMC, is memory efficient, and supports both Jacobi and Gauss-Seidel it... View full abstract»

Statistical Model Checking (SMC) is a computationally very efficient verification technique based on selective system sampling. One well identified shortcoming of SMC is that, unlike probabilistic model checking, it cannot be applied to systems featuring nondeterminism, such as Markov Decision Processes (MDP). We address this limitation by developing an algorithm that resolves nondeterminism proba... View full abstract»

We study the problem of determining approximate equivalences in Markov Decision Processes with rewards using bisimulation metrics. We provide an extension of the framework previously introduced in Ferns et al. (2004), which computes iteratively improving approximations to bisimulation metrics using exhaustive pairwise state comparisons. The similarity between states is determined using the Earth M... View full abstract»

Sound criteria for partial order reduction for probabilistic concurrent systems have been presented in the literature. Their realization relies on a depth-first search-based approach for generating the reduced model. The drawback of this dynamic approach is that it can hardly be combined with other techniques to tackle the state explosion problem, e.g., symbolic probabilistic model checking with m... View full abstract»

Two-variable logic is a fragment of first-order logic that allows for decidable verification problems. In previous work, we developed an approach to FO2 verification that is particularly useful for probabilistic systems, based on analysis of the translation of FO2 to automata. In this work we show that the techniques introduced there can be applied to give information on othe... View full abstract»

These notes develop an approach for characterizing uncertainty in sequences of observable variables. Unlike traditional analyses, observations are not treated as samples from associated random variables. Instead, they are simply assumed to be quantities that satisfy sets of loose constraints. Their exact values remain uncertain and are immaterial to the derived results. When required, additional s... View full abstract»

We investigate a number of problems related to infinite runs of weighted timed automata, subject to lower-bound constraints on the accumulated weight. Closing an open problem from an earlier paper, we show that the existence of an infinite lower-bound-constrained run is -- for us somewhat unexpectedly -- undecidable for weighted timed automata with four or more clocks. This undecidability result a... View full abstract»