10877615
A Decision Procedure for XPath Satisfiability in the Presence of DTD Containing Choice
XPath satisfiability is one of the most basic problems of XML query optimization. A satisfiability decision framework, named SAT-DTD, is proposed to determine, given a set of XPath queries P and a DTD τ, which subset of P are satisfiable by an XML tree conforming to DTD τ. In the framework, an indexed NFA is constructed from the set of XPath queries P, and then the NFA is driven by simple API for DTD (SAD, something like SAX) events, derived from DTD τ, to evaluate the predicates in P and to decide the satisfiability of P. Especially, DTD choice (i.e. '|' operator) is taken into consideration, and an algorithm, named SAT-DTD_C, which bases on SAT-DTD, is put forward to determine the unsatisfiability caused by DTD choice. At last, the complexity of the algorithms is analyzed, and the correctness of the algorithms is tested by experiments.
15870104
Homomorphism Resolving of XPath Trees Based on Automata
As a query language for navigating XML trees and selecting a set of element nodes, XPath is ubiquitous in XML applications. One important issue of XPath queries is containment checking, which is known as a co-NP complete. The homomorphism relationship between two XPath trees, which is a PTIME problem, is a sufficient but not necessary condition for the containment relationship. We propose a new tree structure to depict XPath based on the level of the tree node and adopt a method of sharing the prefixes of multi-trees to construct incrementally the most effective automata, named XTHC (XPath Trees Homomorphism Checker). XTHC takes an XPath tree and produces the result of checking homomorphism relationship between an arbitrary tree in multi-trees and the input tree, thereinto the input tree is transformed into events which force the automata to run. Moreover, we consider and narrow the discrepancy between homomorphism relationship and containment relationship as possible as we can.
14517815
Implementing Atomic Section by Using Hybrid Concurrent Control
Atomic section is an important language feather in multi- thread synchronizing. So far, it can only be implemented by using pessimistic or optimistic concurrent control singly. This paper introduces a flexible hybrid concurrent control system which could harmonize the two modes of concurrent control. Accordingly, a new atomic section is proposed as language level support to open an interface for both manual and compiler-assisted optimization.
8620934
Certifying Concurrent Programs Using Transactional Memory
Transactional memory (TM) is a new promising concurrency-control mechanism that can avoid many of the pitfalls of the traditional lock-based techniques. TM systems handle data races between threads automatically so that programmers do not have to reason about the interaction of threads manually. TM provides a programming model that may make the development of multi-threaded programs easier. Much work has been done to explore the various implementation strategies of TM systems and to achieve better performance, but little has been done on how to formally reason about programs using TM and how to make sure that such reasoning is sound. In this paper, we focus on the semantics of transactional memory and present a proof-carrying code (PCC) system for reasoning about programs using TM. We formalize our reasoning with respect to the TM semantics, prove its soundness, and use examples to demonstrate its effectiveness.
11971991
Formal Reasoning about Concurrent Assembly Code with Reentrant Locks
This paper focuses on the problem of reasoning about concurrent assembly code with reentrant locks. Our verification technique is based on concurrent separation logic (CSL). In CSL, locks are treated as non-reentrant locks and each lock is associated with a resource invariant, the lock-protected resources are obtained and released through acquiring and releasing the lock respectively. In order to accommodate for reentrancy, we introduce some additional notions into our specification language to describe reentrant level for each acquiring and releasing lock operation. Keeping track of the reentrant level for each lock in the pre- and post- conditions enables the program logic to ensure that resources are not reacquired upon reentrancy, thus resources owned by a thread are prevented from reintroducing in the postcondition. Our framework is fully mechanized. Its soundness has been verified using the Coq proof assistant. We demonstrate the usage of our framework through giving a safety proof of a simple program.
15507709
Data-Layout Optimization Using Reuse Distance Distribution
As the ever-increasing gap between the speed of processor and the speed of memory has become the cause of one of primary bottlenecks of computer systems, modern architecture systems use cache to solve this problem, whose utility heavily depends on program data locality. This paper introduces a platform independent data-layout optimization framework to improve program data locality. This framework uses a variable relation model based on variables’ reuse distance distribution to quantitate the relation of variables and accordingly assigns variables which are often accessed together in one group. At the same time this framework introduces a dynamic array regrouping method to group dynamic arrays assigned in a group. Experiments show that this data-layout optimization framework can effectively improve program data locality and program performance.
8166991
On Destination Set in IP-Level Topology Measurement
We present a thorough investigation of four issues with the destination set in IP-level topology measurement. (1) To evaluate the completeness of the destination set, we measured by brute force and found that a half of edges will be missed by the uniform random selection (URS) method which was adopted by well-known CAIDA' skitter. (2) Two potential reasons for edge missing, the short-term routing dynamics and the subnetting technique, were investigated with the last-hop selection method and the bisection selection method respectively. And the results showed that the subnetting technique is the main reason. (3) To select destinations efficiently, we presented the minimum cover selection (MCS) method which performed better than the URS method on 75% of networks over three months. (4) Finally, to investigate the bias of topology characterization, we measured a destination set larger than before and discovered a Chinese topology whose size is 5 times as large as that discovered by skitter. The comparison between characteristics of skitter's topology and ours indicated that the small destination set trends to miss the information on marginal networks.
8300404
Modeling Internet Link Delay Based on Measurement
Understanding Internet link delay is an important key of taking full advantage of Internet resources. In this paper, we find that the link delay follows Gammadistribution using Maximum Likelihood Estimation based on data measured in a large-scale network. The correlations between the link delay and the edge load, the node degree, and the betweenness are analyzed respectively. The link delay distribution parameters for different ranges of edge load are calculated. We findthat the edge load is correlated positively with the shape parameter of link delay Gamma distribution and negatively with the scale parameter.
2560128
Towards Human Decision-Making in Multi-Agent Systems
2 Decision theory finds its roots as a formal topic of research in the fields of economics and psychology. It traditionally relied upon the formal description of decision making embodied principle of maximum expected utility (EUT). But EUT can not capture the common human decision-making attitudes because it does not model the domain of human intuitions – thoughts or preferences that come to mind quickly and without much reflection. This paper models one human’s intuitive attitudes toward risk: risk-aversive and risk-seeking. Rather than immediately making a choice directly from the set of alternatives, agents first form an attitude concerning each possible alternative and likewise solve the corresponding decision problem with a preference order. Correspondingly, this preference order should not be constructed solely on the basis of the individual agent’s own attitudes but with the attitudes of all agents which are relevant. This paper presents our work on above two issues: capturing human intuitive decision-making under risk and extending it to social settings. Finally, we present two experiments that explore risk management behaviors of agents in social settings.
31976355
The Tradeoff of Delta Table Merging and Re-writing Algorithms in What-If Analysis Application
What-if analysis can provide more meaningful information than classical OLAP. Multi-scenario hypothesis based on historical data needs efficient what-if data view support. In general, delta table for what-if analysis is more general than other solutions such as query re-writing prototype of Sesame. Delta table is independent of base table and is more suitable to represent complex hypothetical updates and multi-version hypothetical updates. Due to low efficiency of traditional delta table merging algorithm which is based on set operation, there are few researches focus on delta table merging algorithm but on query re-writing algorithm. By analyzing the difference between what-if query and what-if analysis and improving the delta table merging algorithm, we propose novel algorithms without set operation of difference. Considering the feature of aggregate operations in OLAP analysis, pre-merge algorithm is presented without the generation of what-if data view before group-bys in the scenario of SUM, AVERAGE and COUNT function OLAP queries. In our experiments, the pre-merge algorithm greatly improved the efficiency of delta table merging procedure which is close to base group-by statement and superior to the re-writing algorithm. A complete comparison between all candidate delta table merging algorithms and re-writing algorithm with different what-if update conditions of update, deletion, insertion and mixed what-if updates is exhibited in our experiments, the policy of what-if analysis among different types is also discussed.
14581660
An Improved Physically-Based Method for Geometric Restoration of Distorted Document Images
In document digitization through camera-based systems, simple imaging setups often produce geometric distortions in the resultant 2D images because of the nonplanar geometric shapes of certain documents such as thick bound books, rolled, folded, or crumpled materials, etc. Previous work [1], [2], [3], [4] has demonstrated that arbitrary warped documents can be successfully restored by flattening a 3D scan of the document. These approaches use physically-based or relaxation-based techniques in their flattening process. While this has been demonstrated to be effective in rectifying the image content and improving OCR, these previous approaches have several limitations in terms of speed and stability. In this paper, we propose a distance-based penalty metric to replace the mass- spring model and introduce additional bending resistance and drag forces to improve the efficiency of the existing approaches. The use of Verlet integration and special plane collision handling schemes also help to achieve better stability without sacrificing efficiency. Experiments on various document images captured from books, brochures, and historical documents with arbitrary warpings have demonstrated large improvements over the existing approaches in terms of stability and efficiency.