14603294
UMM: an operational memory model specification framework with integrated model checking capability
Given the complicated nature of modern shared memory systems, it is vital to have a systematic approach to specifying and analyzing memory consistency requirements. In this paper, we present the UMM specification framework, which integrates two key features to support memory model verification: (i) it employs a simple and generic memory abstraction that can capture a large collection of memory models as guarded commands with a uniform notation, and (ii) it provides built-in model checking capability to enable formal reasoning about thread behaviors. Using this framework, memory models can be specified in a parameterized style—designers can simply redefine a few bypassing rules and visibility ordering rules to obtain an executable specification of another memory model. We formalize several classical memory models, including Sequential Consistency, Coherence, and PRAM, to illustrate the general techniques of applying this framework. We then provide an alternative specification of the Java memory model, based on a proposal from Manson and Pugh, and demonstrate how to analyze Java thread semantics using model checking. We also compare our operational specification style with axiomatic specification styles and explore a mechanism that converts a memory model definition from one style to the other. Copyright © 2005 John Wiley & Sons, Ltd.
1536411
Specifying Java thread semantics using a uniform memory model
Standardized language level support for threads is one of the most important features of Java. However, defining the Java Memory Model (JMM) has turned out to be a major challenge. Several models produced to date are not as easily comprehensible and comparable as first thought. Given the growing interest in multithreaded Java programming, it is essential to have a sound framework that would allow formal specification and reasoning about the JMM.This paper presents the Uniform Memory Model (UMM), a generic memory model specification framework. Based on guarded commands, UMM can be easily integrated with a model checking utility, providing strong built-in support for formal verification and program analysis. With a flexible and simple architecture, UMM is configurable to capture different memory consistency requirements for both architectural and language level memory models. An alternative formal specification of the JMM, primarily based on the semantics proposed by Manson and Pugh, is implemented in UMM. Systematic analysis has revealed interesting properties of the proposed semantics. Inconsistencies from the original specification have also been uncovered.
6730244
Nemos: a framework for axiomatic and executable specifications of memory consistency models
Summary form only given. Conforming to the underlying memory consistency rules is a fundamental requirement for implementing shared memory systems and developing multiprocessor programs. In order to promote understanding and enable automated verification, it is highly desirable that a memory model specification be both declarative and executable. We present a specification framework called Nemos (Nonoperational yet Executable Memory Ordering Specifications), which supports precise specification and automatic execution in the same framework. We employ a uniform notation based on predicate logic to define shared memory semantics in an axiomatic as well as compositional style. We also apply constraint logic programming and SAT solving to make the axiomatic specifications executable for memory model analysis. To illustrate our approach, we formalize a collection of classical memory models, including sequential consistency, coherence, PRAM, causal consistency, and processor consistency.
1466008
Analyzing the Intel Itanium Memory Ordering Rules Using Logic Programming and SAT
We present a non-operational approach to specifying and analyzing shared memory consistency models. The method uses higher order logic to capture a complete set of ordering constraints on execution traces, in an axiomatic style. A direct encoding of the semantics with a constraint logic programming language provides an interactive and incremental framework for exercising and verifying finite test programs. The framework has also been adapted to generate equivalent boolean satisfiability (SAT) problems. These techniques make a memory model specification executable, a powerful feature lacked in most non-operational methods. As an example, we provide a concise formalization of the Intel Itanium memory model and show how constraint solving and SAT solving can be effectively applied for computer aided analysis. Encouraging initial results demonstrate the scalability for complex industrial designs.
61052099
Memory-Model-Sensitive Data Race Analysis
We present a “memory-model-sensitive” approach to validating correctness properties for multithreaded programs. Our key insight is that by specifying both the inter-thread memory consistency model and the intra-thread program semantics as constraints, a program verification task can be reduced to an equivalent constraint solving problem, thus allowing an exhaustive examination of all thread interleavings precisely allowed by a given memory model. To demonstrate, this paper formalizes race conditions according to the new Java memory model, for a simplified but non-trivial source language. We then describe the implementation of a memory-model-sensitive race detector using constraint logic programming (CLP). In comparison with conventional program analysis, our approach does not offer the same kind of performance and scalability due to the complexity involved in exact formal reasoning. However, we show that a formal semantics can serve more than documentation purposes — it can be applied as a sound basis for rigorous property checking, upon which more scalable methods can be derived.
156436
Learning Multiple Related Tasks using Latent Independent Component Analysis
We propose a probabilistic model based on Independent Component Analysis for learning multiple related tasks. In our model the task parameters are assumed to be generated from independent sources which account for the relatedness of the tasks. We use Laplace distributions to model hidden sources which makes it possible to identify the hidden, independent components instead of just modeling correlations. Furthermore, our model enjoys a sparsity property which makes it both parsimonious and robust. We also propose efficient algorithms for both empirical Bayes method and point estimation. Our experimental results on two multi-label text classification data sets show that the proposed approach is promising.
30442545
On Kotzig's conjecture concerning graphs with a unique regular path-connectivity
Abstract Kotzig (see Bondy and Murty, Graph Theory with Applications, North-Holland, Amsterdam, 1976) conjectured that there exists no graph with the property that every pair of vertices is connected by a unique path of length k, k>2 . Kotzig (Graph Theory and Related Topics, Academic Press, New York, 1979, pp. 358–367) has proved this conjecture for 2 . Xing and Hu (Discrete Math. 135 (1994) 387–393) have proved it for k>11 . Here we prove this conjecture for the remaining cases k=9,10,11 .
150914
An enhanced model for searching in semantic portals
Semantic Portal is the next generation of web portals that are powered by Semantic Web technologies for improved information sharing and exchange for a community of users. Current methods of searching in Semantic Portals are limited to keyword-based search using information retrieval (IR) techniques, ontology-based formal query and reasoning, or a simple combination of the two. In this paper, we propose an enhanced model that tightly integrates IR with formal query and reasoning to fully utilize both textual and semantic information for searching in Semantic Portals. The model extends the search capabilities of existing methods and can answer more complex search requests. The ideas in a fuzzy description logic (DL) IR model and a formal DL query method are employed and combined in our model. Based on the model, a semantic search service is implemented and evaluated. The evaluation shows very large improvements over existing methods.
14477293
To Select or To Weigh: A Comparative Study of Model Selection and Model Weighing for SPODE Ensembles
An ensemble of Super-Parent-One-Dependence Estimators (SPODEs) offers a powerful yet simple alternative to naive Bayes classifiers, achieving significantly higher classification accuracy at a moderate cost in classification efficiency. Currently there exist two families of methodologies that ensemble candidate SPODEs for classification. One is to select only helpful SPODEs and uniformly average their probability estimates, a type of model selection. Another is to assign a weight to each SPODE and linearly combine their probability estimates, a methodology named model weighing. This paper presents a theoretical and empirical study comparing model selection and model weighing for ensembling SPODEs. The focus is on maximizing the ensemble's classification accuracy while minimizing its computational time. A number of representative selection and weighing schemes are studied, providing a comprehensive research on this topic and identifying effective schemes that provide alternative trades-off between speed and expected error.
7655844
Music emotion classification: a fuzzy approach
Due to the subjective nature of human perception, classification of the emotion of music is a challenging problem. Simply assigning an emotion class to a song segment in a deterministic way does not work well because not all people share the same feeling for a song. In this paper, we consider a different approach to music emotion classification. For each music segment, the approach determines how likely the song segment belongs to an emotion class. Two fuzzy classifiers are adopted to provide the measurement of the emotion strength. The measurement is also found useful for tracking the variation of music emotions in a song. Results are shown to illustrate the effectiveness of the approach.