The Entity Registry System: Implementing 5-Star Linked Data Without the Web

Linked Data applications often assume that connectivity to data repositories and entity resolution services are always available. This may not be a valid assumption in many cases. Indeed, there are about 4.5 billion people in the world who have no or limited Web access. Many data-driven applications may have a critical impact on the life of those people, but are inaccessible to those populations due to the architecture of today's data registries. In this paper, we propose and evaluate a new open-source system that can be used as a general-purpose entity registry suitable for deployment in poorly-connected or ad-hoc environments.Comment: 16 pages, authors are listed in alphabetical orde

Unifying Requirements and Code: an Example

Requirements and code, in conventional software engineering wisdom, belong to entirely different worlds. Is it possible to unify these two worlds? A unified framework could help make software easier to change and reuse. To explore the feasibility of such an approach, the case study reported here takes a classic example from the requirements engineering literature and describes it using a programming language framework to express both domain and machine properties. The paper describes the solution, discusses its benefits and limitations, and assesses its scalability.Comment: 13 pages; 7 figures; to appear in Ershov Informatics Conference, PSI, Kazan, Russia (LNCS), 201

Concurrence control for transactions with priorities

Priority inversion occurs when a process is delayed by the actions of another process with less priority. With atomic transactions, the concurrency control mechanism can cause delays, and without taking priorities into account can be a source of priority inversion. Three traditional concurrency control algorithms are extended so that they are free from unbounded priority inversion

Predicate Detection for Parallel Computations with Locking Constraints

The happened-before model (or the poset model) has been widely used for modeling the computations (execution traces) of parallel programs and detecting predicates (user-specified conditions). This model captures potential causality as well as locking constraints among the executed events of computations using Lamport\u27s happened-before relation. The detection of a predicate in a computation is performed by checking if the predicate could become true in any reachable global state of the computation. In this paper, we argue that locking constraints are fundamentally different from potential causality. Hence, a poset is not an appropriate model for debugging purposes when the computations contain locking constraints. We present a model called Locking Poset, or a Loset, that generalizes the poset model for locking constraints. Just as a poset captures possibly an exponential number of total orders, a loset captures possibly an exponential number of posets. Therefore, detecting a predicate in a loset is equivalent to detecting the predicate in all corresponding posets. Since determining if a global state is reachable in a computation is a fundamental problem for detecting predicates, this paper first studies the reachability problem in the loset model. We show that the problem is NP-complete. Afterwards, we introduce a subset of reachable global states called lock-free feasible global states such that we can check whether a global state is lock-free feasible in polynomial time. Moreover, we show that lock-free feasible global states can act as "reset" points for reachability and be used to drastically reduce the time for determining the reachability of other global states. We also introduce strongly feasible global states that contain all reachable global states and show that the strong feasibility of a global state can be checked in polynomial time. We show that strong feasibility provides an effective approximation of reachability for many practical applications

Incremental bounded model checking for embedded software

Program analysis is on the brink of mainstream usage in embedded systems development. Formal verification of behavioural requirements, finding runtime errors and test case generation are some of the most common applications of automated verification tools based on bounded model checking (BMC). Existing industrial tools for embedded software use an off-the-shelf bounded model checker and apply it iteratively to verify the program with an increasing number of unwindings. This approach unnecessarily wastes time repeating work that has already been done and fails to exploit the power of incremental SAT solving. This article reports on the extension of the software model checker CBMC to support incremental BMC and its successful integration with the industrial embedded software verification tool BTC EMBEDDED TESTER. We present an extensive evaluation over large industrial embedded programs, mainly from the automotive industry. We show that incremental BMC cuts runtimes by one order of magnitude in comparison to the standard non-incremental approach, enabling the application of formal verification to large and complex embedded software. We furthermore report promising results on analysing programs with arbitrary loop structure using incremental BMC, demonstrating its applicability and potential to verify general software beyond the embedded domain

Predicate detection for parallel computations

One of the fundamental problems in runtime verification of parallel program is to check if a predicate could become true in any global state of the system. The problem is challenging because of the nondeterministic process or thread scheduling of the system. Predicate detection alleviates this problem by analyzing the computation of the program and predicting whether the predicate could become true by exercising an alternative process schedule. The technique was first introduced by Cooper et al. and Garg et al. for distributed debugging. Later, jPredictor applies this technique for concurrent debugging. We improve the technique of predicate detection in three ways. The first part of this dissertation presents the first online-and-parallel predicate detector for general-purpose predicate detection, named ParaMount. ParaMount partitions the set of consistent global states and each subset can be enumerated in parallel using existing sequential enumeration algorithms. Our experimental results show that ParaMount speeds up the existing sequential algorithms by a factor of 6 with 8 threads. Moreover, Paramount can run along with the execution of users’ program and hence it is applicable even to non-terminating programs. The second part develops a fast enumeration algorithm, named QuickLex, for consistent global states. In comparison with the original lexical algorithm (Lex), QuickLex uses an additional O(n2) space to reduce the time complexity from O(n2) to O(n·∆(P)), where n is the number of processes or threads in the computation and ∆(P) is the maximal number of incoming edges of any event. The third part introduces Loset — a new model for parallel computations with locking constraints. We show that the reachability problem in a loset is NP-complete. To tackle the NP-completeness, we present several useful properties. Specifically, if the final global state is reachable, then all lock-free feasible global states are reachable. In addition, we show that the reachability of a global state G can be determined using a sub-computation instead of the entire computation. Moreover, we introduce the strong feasibility of a global state, which is an upper approximation of reachability that can be calculated efficiently. Our experiments show that the property accurately models the reachability for all 11 benchmarks.Electrical and Computer Engineerin

Deadlock detection of Java Bytecode

This paper presents a technique for deadlock detection of Java programs. The technique uses typing rules for extracting infinite-state abstract models of the dependencies among the components of the Java intermediate language -- the Java bytecode. Models are subsequently analysed by means of an extension of a solver that we have defined for detecting deadlocks in process calculi. Our technique is complemented by a prototype verifier that also covers most of the Java features.Comment: Pre-proceedings paper presented at the 27th International Symposium on Logic-Based Program Synthesis and Transformation (LOPSTR 2017), Namur, Belgium, 10-12 October 2017 (arXiv:1708.07854