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98

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Introduction

Additional affiliations

September 2012 - June 2015

January 2011 - August 2013

January 2011 - August 2013

## Publications

Publications (98)

Source code summarization aims to generate concise descriptions for code snippets in natural language, thereby facilitates program comprehension and software maintenance. In this paper, we propose a novel approach GSCS to automatically generate summaries for Java methods, which leverages both semantic and structural information of the code snippets...

The process of completing, correcting and prioritising specifications is an essential but very complex task for the maintenance and improvement of software systems. The preservation of functionalities and the ability to accommodate changes are main objectives of the software development cycle to guarantee system reliability. Logical theories able t...

Deep Reinforcement Learning (DRL) has recently obtained considerable attentions. It empowers Reinforcement Learning (RL) with Deep Learning (DL) techniques to address various difficult tasks. In this paper, a novel approach called the Genetic Algorithm of Neuron Coverage (GANC) is proposed. It is motivated for improving the robustness and performan...

Developers often need to use appropriate APIs to program efciently, but it is usually a difcult task to identify the exact one they need from a vast list of candidates. To ease the burden, a multitude of API recommendation approaches have been proposed. However, most of the currently available API recommenders do not support the effective integrati...

\begin{abstract} In recent years, the Finger Texture (FT) has attracted considerable attention as a biometric characteristic. It can provide efficient human recognition performance, because it has different human-specific features of apparent lines, wrinkles and ridges distributed along the inner surface of all fingers. Also, such pattern structure...

Developers often need to use appropriate APIs to program efficiently, but it is usually a difficult task to identify the exact one they need from a vast of candidates. To ease the burden, a multitude of API recommendation approaches have been proposed. However, most of the currently available API recommenders do not support the effective integratio...

In the current mobile app development, novel and emerging DevOps practices (e.g., Continuous Delivery, Integration, and user feedback analysis) and tools are becoming more widespread. For instance, the integration of user feedback (provided in the form of user reviews) in the software release cycle represents a valuable asset for the maintenance an...

Observabililty is an important topic of Boolean control networks (BCNs). In this paper, we propose a new type of observability named online observability to present the sufficient and necessary condition of determining the initial states of BCNs, when their initial states cannot be reset. And we design an algorithm to decide whether a BCN has the o...

In the current mobile app development, novel and emerging DevOps practices (e.g., Continuous Delivery, Integration, and user feedback analysis) and tools are becoming more widespread. For instance, the integration of user feedback (provided in form of user reviews) in the software release cycle represents a valuable asset for the maintenance and ev...

Application programming interfaces (APIs) documentation is the official reference of the APIs. Defects in API documentation pose serious hurdles to the comprehension and usage of APIs. In this paper, we present DRONE, a tool that automatically detects the directive defects in APIs documents and recommends repair solutions to fix them. Particularly,...

Application Programming Interfaces (APIs) represent key tools for software developers to build complex software systems. However, several studies have revealed that even major API providers tend to have incomplete or inconsistent API documentation. This can severely hamper the API comprehension and, as a consequence, the quality of the software bui...

Finger Texture (FT) is currently attracting significant attentions in the area of human recognition. Finger texture covers the area between the lower knuckle of the finger and the upper phalanx before the fingerprint. It involves rich features which can be efficiently used as a biometric characteristic. In this paper, we contribute to this growing...

Application Programming Interface (API) documents represent one of the most important references for API users. However, it is frequently reported that the documentation is inconsistent with the source code and deviates from the API itself. Such inconsistencies in the documents inevitably confuse the API users hampering considerably their API compr...

Using a SAT-solver on top of a partial previously-known solution we improve the upper bound of the packing chromatic number of the infinite square lattice from 17 to 15. We discuss the merits of SAT-solving for this kind of problem as well as compare the performance of different encodings. Further, we improve the lower bound from 12 to 13 again usi...

Behaviour distances to measure the resemblance of two states in a (nondeterministic) fuzzy transition system have been proposed recently in the literature. Such a distance, defined as a pseudo-ultrametric over the state space of the model, provides a quantitative analogue of bisimilarity. In this paper, we focus on the problem of computing these di...

In order to detect malicious insider attacks it is
important to model and analyse infrastructures and policies
of organisations and the insiders acting within them. We extend formal approaches that allow modelling such scenarios
by quantitative aspects to enable a precise analysis of security designs. Our framework enables evaluating the risks of a...

Software is often governed by and thus adapts to phenomena that occur at runtime. Unlike traditional decision problems, where a decision-making model is determined for reasoning, the adaptation logic of such software is concerned with empirical data and is subject to practical constraints. We present an Iterative Decision-Making Scheme (IDMS) that...

Using a SAT-solver on top of a partial previously-known solution we improve
the upper bound of the packing chromatic number of the infinite square lattice
from 17 to 16.

Malicious insider threats are difficult to detect and to mitigate. Many approaches for explaining behaviour exist, but there is little work to relate them to formal approaches to insider threat detection. In this work we present a general formal framework to perform analysis for malicious insider threats, based on probabilistic modelling, verificat...

Modelling, reasoning and verifying complex situations involving a system of agents is crucial in all phases of the development of a number of safety-critical systems. In particular, it is of fundamental importance to have tools and techniques to reason about the doxastic and epistemic states of agents, to make sure that the agents behave as intende...

A general method is established to derive a ground-complete axiomatization
for a weak semantics from such an axiomatization for its concrete counterpart,
in the con- text of the process algebra BCCS. This transformation moreover
preserves {\omega}-completeness. It is applicable to semantics at least as
coarse as impossible futures semantics. As an...

We place the continuous-time orbit problem in P, sharpening the decidability result shown
by Hainry [7].

Probabilistic model checking is a verification technique that has been the focus of intensive research for over a decade. One important issue with probabilistic model checking, which is crucial for its practical significance but is overlooked by the state-of-the-art largely, is the potential discrepancy between a stochastic model and the real-world...

We investigate the complexity of computing entropy of various Markovian models including Markov Chains (MCs), Interval Markov Chains (IMCs) and Markov Decision Processes (MDPs). We consider both entropy and entropy rate for general MCs, and study two algorithmic questions, i.e., entropy approximation problem and entropy threshold problem. The forme...

Perturbation analysis in probabilistic verification addresses the robustness and sensitivity problem for verification of stochastic models against qualitative and quantitative properties. We identify two types of perturbation bounds, namely non-asymptotic bounds and asymptotic bounds. Non-asymptotic bounds are exact, pointwise bounds that quantify...

We develop a model-based framework which supports approximate quantitative verification of implantable cardiac pacemaker models over hybrid heart models. The framework is based on hybrid input-output automata and can be instantiated with user-specified pacemaker and heart models. For the specifications, we identify two property patterns which are t...

Labelled Markov chains (LMCs) are widely used in probabilistic verification, speech recognition, computational biology, and many other fields. Checking two LMCs for equivalence is a classical problem subject to extensive studies, while the total variation distance provides a natural measure for the "inequivalence" of two LMCs: it is the maximum dif...

Solvency games, introduced by Berger et al., provide an abstract framework
for modelling decisions of a risk-averse investor, whose goal is to avoid ever
going broke. We study a new variant of this model, where, in addition to
stochastic environment and fixed increments and decrements to the investor's
wealth, we introduce interest, which is earned...

We study strategy synthesis for stochastic two-player games with multiple objectives expressed as a conjunction of LTL and expected total reward goals. For stopping games, the strategies are constructed from the Pareto frontiers that we compute via value iteration. Since, in general, infinite memory is required for deterministic winning strategies...

We study two-player stochastic games, where the goal of one player is to satisfy a formula given as a positive boolean combination of expected total reward objectives and the behaviour of the second player is adversarial. Such games are important for modelling, synthesis and verification of open systems with stochastic behaviour. We show that findi...

Markov decision processes (MDPs) are often used for modelling distributed systems with probabilistic failure or randomisation. We consider the problem of model repair for MDPs defined as follows: if the MDP fails to satisfy a property, we aim to find new values for the transition probabilities so that the property is guaranteed to hold, while at th...

We investigate the complexity of model checking (finite) interval-valued discrete time Markov chains, that is, discrete time Markov chains where each transition is associated with an interval in which the actual transition probability must lie. Two semantics are considered, the uncertain Markov chain (UMC) semantics and the interval Markov decision...

We develop a novel hybrid heart model in Simulink that is suitable for quantitative verification of implantable cardiac pacemakers. The heart model is formulated at the level of cardiac cells, can be adapted to patient data, and incorporates stochasticity. It is inspired by the timed and hybrid automata network models of Jiang et al and Ye et al, w...

We present PRISM-games, a model checker for stochastic multi-player games, which supports modelling, automated verification and strategy synthesis for probabilistic systems with competitive or cooperative behaviour. Models are described in a probabilistic extension of the Reactive Modules language and properties are expressed using rPATL, which ext...

In this letter, we revisit the {\em orbit problem}, which was studied in
\cite{HAR69,SHA79,KL86}. In \cite{KL86}, Kannan and Lipton proved that this
problem is decidable in polynomial time. In this paper, we study the {\em
approximate orbit problem}, and show that this problem is decidable except for
one case.

Implantable medical devices, such as cardiac pacemakers, must be designed and programmed to the highest levels of safety and reliability. Recently, errors in embedded software have led to a substantial increase in safety alerts, costly device recalls or even patient death. To address such issues, we propose a model-based framework for quantitative,...

We study stochastic two-player games where the goal of one player is to achieve precisely a given expected value of the objective function, while the goal of the opponent is the opposite. Potential applications for such games include controller synthesis problems where the optimisation objective is to maximise or minimise a given payoff function wh...

Stochastic branching processes are a classical model for describing random
trees, which have applications in numerous fields including biology, physics,
and natural language processing. In particular, they have recently been
proposed to describe parallel programs with stochastic process creation. In
this paper, we consider the problem of model chec...

Stochastic modeling and algorithmic verification techniques have been proved useful in analyzing and detecting unusual trends in performance and energy usage of systems such as power management controllers and wireless sensor devices. Many important properties are dependent on the cumulated time that the device spends in certain states, possibly in...

We present automatic verification techniques for the modelling and analysis of probabilistic systems that incorporate competitive behaviour. These systems are modelled as turn-based stochastic multi-player games, in which the players can either collaborate or compete in order to achieve a particular goal. We define a temporal logic called rPATL for...

We propose a compositional specification theory for reasoning about components that interact by synchronisation of input and output (I/O) actions, in which the specification of a component constrains the temporal ordering of interactions with the environment. Such a theory is motivated by the need to support composability of components, in addition...

We supply details of a compositional specification theory we have been working on for modelling connectors and components. This supports the operations of parallel composition, for examining the structural behaviour of networked systems, logical conjunction, for supporting independent development of components, and quotient for incremental developm...

We propose a novel stochastic extension of timed automata, i.e. Markovian Timed Automata (MTA). We study the problem of optimizing the reachability probabilities in this model. Two variants are considered, namely, the timebounded and unbounded reachability. In each case, we propose Bellman equations to characterize the probability. For the former,...

This paper considers the verification of continuous-time Markov decision process (CTMDPs) against single-clock deterministic timed automata (DTA) specifications. The central issue is to compute the maximum probability of the set of timed paths of a CTMDP C that are accepted by a DTA A. We show that this problem can be reduced to a linear programmin...

In this paper we study time-bounded verification of a finite continuous-time Markov chain (CTMC) C against a real-time specification, provided either as a metric temporal logic (MTL) property φ, or as a timed automaton (TA) A. The key question is: what is the probability of the set of timed paths of C that satisfy φ (or are accepted by A) over a ti...

Multi-agent systems are an increasingly important software paradigm and in many of its applications agents cooperate to achieve a particular goal. This requires the design of efficient collaboration protocols, a typical example of which is team formation. In this paper, we illustrate how probabilistic model checking, a technique for formal verifica...

This paper contributes to the study of the equational theory of the priority operator of Baeten, Bergstra and Klop in the setting of the process algebra BCCSP. It is shown that, in the presence of at least two actions, the collection of process equations over BCCSP with the priority operator that are valid modulo bisimilarity, irrespective of the c...

This paper makes verifying continuous-time Markov chains (CTMCs) against deterministic timed automata (DTA) objectives practical.
We show that verifying 1-clock DTA can be done by analyzing subgraphs of the product of CTMC C{\mathcal C} and the region graph of DTA A{\mathcal A}. This improves upon earlier results and allows to only use standard ana...

We study the verification of a finite continuous-time Markov chain (CTMC) C
against a linear real-time specification given as a deterministic timed
automaton (DTA) A with finite or Muller acceptance conditions. The central
question that we address is: what is the probability of the set of paths of C
that are accepted by A, i.e., the likelihood that...

We investigate Semi-Markov Decision Processes (SMDPs). Two problems are studied, namely, the time-bounded reachability problem
and the long-run average fraction of time problem. The former aims to compute the maximal (or minimum) probability to reach
a certain set of states within a given time bound. We obtain a Bellman equation to characterize the...

We investigate the problem of verifying linear-time properties against inhomogeneous continuous-time Markov chains (ICTMCs).
A fundamental question we address is how to compute reachability probabilities. We consider two variants: time-bounded and
unbounded reachability. It turns out that both can be characterized as the least solution of a system...

We study the following problem: given a continuous-time Markov chain (CTMC) C, and a linear real-time property provided as a deterministic timed automaton (DTA) A, what is the probability of the set of paths of C that are accepted by A (C satisfies A)? It is shown that this set of paths is measurable and computing its probability can be reduced to...

Priced Probabilistic Timed Automata (PPTA) extend timed automata with cost-rates in locations and discrete probabilistic branching.
The model is a natural combination of Priced Timed Automata and Probabilistic Timed Automata. In this paper we focus on cost-bounded
probabilistic reachability for PPTA, which determines if the maximal probability to r...

In this paper, we consider the behavioral pseudometrics for probabilistic systems, which are a quantitative analogue of probabilistic bisimilarity in the sense that the distance zero captures the probabilistic bisimilarity. The model we are interested in is probabilistic automata, which are based on state transition systems and make a clear distinc...

Recently, Aceto, Fokkink & Ing´ olfsd´ ottir proposed an algo- rithm to turn any sound and ground-complete axiomatisa- tion of any preorder listed in the linear time - branching time spectrum at least as coarse as the ready simulation preorder, into a sound and ground-complete axiomatisa- tion of the corresponding equivalence—its kernel. More- over...

We provide a finite basis for the (in)equational theory of the process algebra BCCS modulo the weak failures preorder and equivalence. We also give positive and negative results regarding the axiomatizability of BCCS modulo weak impossible futures semantics.

Control of timed systems has become a very active research area. In this paper, we revisit the complexity of safety and reachability control problems for timed automata. Generally, these problems turn out to be exptime-complete and we aim at finding tractable subclasses which admit efficient control. To this purpose, we consider the control for tim...

We investigate the (in)equational theory of impossible futures semantics over the process algebra BCCSP. We prove that no finite, sound axiomatization for BCCSP modulo impossible futures equivalence is ground-complete. By contrast, we present a finite, sound, ground-complete axiomatization for BCCSP modulo impossible futures preorder. If the alphab...

We present a thorough study of propositional dynamic logic over a variation of labeled transition systems, called accelerated labelled transition systems, which are transition systems labeled with regular expressions over action labels. We study the model checking and satisfiability decision problems. Through a notion of regular expression rewritin...

This paper focuses on probabilistic timed automata (PTA), an extension of timed automata with discrete probabilistic branchings. As the regions of these automata often lead to an exponential blowup, reduction techniques are of utmost importance. In this paper, we investigate probabilistic time-abstracting bisimulation (PTaB), an equivalence notion...

Van Glabbeek presented the linear time–branching time spectrum of behavioral semantics. He studied these semantics in the setting of the basic process algebra BCCSP, and gave finite, sound and ground-complete, axiomatizations for most of these semantics. Groote proved for some of van Glabbeek's axiomatizations that they are ω-complete, meaning that...

We study the divergent-sensitive spectrum of weak bisimulation equivalences in the setting of process algebra. To represent the infinite behavior, we consider the prefix iteration extension of a fragment of Milner's CCS. The prefix iteration operator is a variant on the binary version of the Kleene star operator obtained by restricting the first ar...

This paper studies the equational theory of bisimulation equivalence over the process algebra BCCSP extended with the prior- ity operator of Baeten, Bergstra and Klop. It is proven that, in the presence of an inflnite set of actions, bisimulation equivalence has no flnite, sound, ground-complete equational axiomatization over that lan- guage. This...

Last decade witnesses an impressive development of embedded reactive systems, which motivates the research of open systems, where multiple components interact with each other and their environment and these interactions decide the behavior of the system. A natural "common-denominator" model for open systems is the concurrent game structure, in whic...

In this paper, we consider the behavioral pseudometrics for probabilistic systems. The model we are interested in is probabilistic automata, which are based on state transition systems and make a clear distinction between probabilistic and nondeterministic choices. The pseudometrics are defined as the greatest fixpoint of a monotonic functional on...

In this paper, we provide a transformation from the branching bisimulation problem for infinite, concurrent, data-intensive systems in linear process format, into solving Parameterized Boolean Equation Systems. We prove correctness, and illustrate the approach with an unbounded queue example. We also provide some adaptations to obtain similar trans...

This paper focuses on the so called controller synthesis problem, which addresses the question of how to limit the internal behavior of a given system implementation to meet its
specification, regardless of the behavior enforced by the environment. We consider this problem in the probabilistic setting,
where the underlying model has both probabilis...

This paper studies the equational theory of bisimulation equivalence over the process algebra BCCSP extended with the priority operator of Baeten, Bergstra and Klop. It is proven that, in the presence of an infinite set of actions, bisimulation equivalence has no finite, sound, ground-complete equational axiomatization over that language. This nega...

We prove that the equational theory of the process algebra BCCSP modulo completed simulation equivalence does not have a finite basis. Furhermore, we prove that with a finite alphabet of actions, the equational theory of BCCSP modulo ready simulation equivalence does not have a finite basis. In contrast, with an infinite alphabet, the latter equati...