3386880
Statistical Learning Techniques for Costing XML Queries
Developing cost models for query optimization is significantly harder for XML queries than for traditional relational queries. The reason is that XML query operators are much more complex than relational operators such as table scans and joins. In this paper, we propose a new approach, called COMET, to modeling the cost of XML operators; to our knowledge, COMET is the first method ever proposed for addressing the XML query costing problem. As in relational cost estimation, COMET exploits a set of system catalog statistics that summarizes the XML data; the set of "simple path" statistics that we propose is new, and is well suited to the XML setting. Unlike the traditional approach, COMET uses a new statistical learning technique called "transform regression" instead of detailed analytical models to predict the overall cost. Besides rendering the cost estimation problem tractable for XML queries, COMET has the further advantage of enabling the query optimizer to be self-tuning, automatically adapting to changes over time in the query workload and in the system environment. We demonstrate COMET's feasibility by developing a cost model for the recently proposed XNAV navigational operator. Empirical studies with synthetic, benchmark, and real-world data sets show that COMET can quickly obtain accurate cost estimates for a variety of XML queries and data sets.
598542
XSEED: Accurate and Fast Cardinality Estimation for XPath Queries
We propose XSEED, a synopsis of path queries for cardinality estimation that is accurate, robust, efficient, and adaptive to memory budgets. XSEED starts from a very small kernel, and then incrementally updates information of the synopsis. With such an incremental construction, a synopsis structure can be dynamically configured to accommodate different memory budgets. Cardinality estimation based on XSEED can be performed very efficiently and accurately. Extensive experiments on both synthetic and real data sets show that even with less memory, XSEED could achieve accuracy that is an order of magnitude better than that of other synopsis structures. The cardinality estimation time is under 2% of the actual querying time for a wide range of queries in all test cases.
11505780
InterJoin: Exploiting Indexes and Materialized Views in XPath Evaluation
XML has become the standard for data exchange for a wide variety of applications, particularly in the scientific community. In order to efficiently process queries on XML representations of scientific data, we require specialized techniques for evaluating XPath expressions. Exploiting materialized views in query processing significantly enhances query processing performance. We propose a novel view definition that allows for intermediate (structural) join results to be stored and reused in XML query evaluation. Unlike current XML view proposals, our views do not require navigation in the original document or path-based pattern matching. Hence, they are evaluated significantly faster and are easily costed as part of a query plan. In general, current structural joins cannot exploit views efficiently when the view definition is not a prefix (or a suffix) of the XPath query. To increase the applicability of our proposed view definition, we propose a novel physical structural join operator called InterJoin. The InterJoin operator allows for joining interleaving XPath expressions, e.g., joining //A//C with //B to evaluate //A//B//C. InterJoin allows for more join alternatives in XML query plans. We propose several physical implementations for InterJoin, including a technique to exploit spatial indexes on the inputs. We give analytic cost models for the implementations so they can be costed in an existing XML query optimizer. Experiments on real and synthetic XML data show significant speed-ups of up to 200% using InterJoin, and speed-ups of up to 400% using our materialized views
5631107
Compact Access Control Labeling for Efficient Secure XML Query Evaluation
Fine-grained access controls for XML define access privileges at the granularity of individual XML nodes. In this paper, we present a fine-grained access control mechanism for XML data. This mechanism exploits the structural locality of access rights as well as correlations among the access rights of different users to produce a compact physical encoding of the access control data. This encoding can be constructed using a single pass over a labeled XML database. It is block-oriented and suitable for use in secondary storage. We show how this access control mechanism can be integrated with a next-of-kin (NoK) XML query processor to provide efficient, secure query evaluation. The key idea is that the structural information of the nodes and their encoded access controls are stored together so the access privileges can be checked efficiently. Our evaluation shows that the access control mechanism introduces little overhead into the query evaluation process.
5525123
FIX: feature-based indexing technique for XML documents
Indexing large XML databases is crucial for efficient evaluation of XML twig queries. In this paper, we propose a feature-based indexing technique, called FIX, based on spectral graph theory. The basic idea is that for each twig pattern in a collection of XML documents, we calculate a vector of features based on its structural properties. These features are used as keys for the patterns and stored in a B+tree. Given an XPath query, its feature vector is first calculated and looked up in the index. Then a further refinement phase is performed to fetch the final results. We experimentally study the indexing technique over both synthetic and real data sets. Our experiments show that FIX provides great pruning power and could gain an order of magnitude performance improvement for many XPath queries over existing evaluation techniques.
35884730
Compact access control labeling for efficient secure XML query evaluation
Fine-grained access controls for XML define access privileges at the granularity of individual XML nodes. In this paper, we present a fine-grained access control mechanism for XML data. This mechanism exploits the structural locality of access rights as well as correlations among the access rights of different users to produce a compact physical encoding of the access control data. This encoding can be constructed using a single pass over a labeled XML database. It is block-oriented and suitable for use in secondary storage. We show how this access control mechanism can be integrated with a next-of-kin (NoK) XML query processor to provide efficient, secure query evaluation. The key idea is that the structural information of the nodes and their encoded access controls are stored together, allowing the access privileges to be checked efficiently. Our evaluation shows that the access control mechanism introduces little overhead into the query evaluation process.
1064501
Trade-off scheme for fault tolerant connected dominating sets on size and diameter
Connected Dominating Set (CDS) has been a well known approach for constructing a virtual backbone to alleviate the broadcasting storm in wireless networks. Current research has focused on minimizing the size and diameter or improving the fault tolerance of CDS. However, to our best knowledge, no existing research has considered these three important factors together in a single model. In this paper, we introduce the fault tolerant model studying a joint optimization problem in which the objective is to minimize the CDS size as well as the network latency. This model also addresses the tradeoffs between the objective functions. We next propose one approximation algorithm and two distributed algorithms with constant ratios for the model. Simulation results show that our algorithms can gain good tradeoffs between the three factors, which coincide with theoretical analysis. Moreover, our algorithms could obtain a better performance than previous work.
1811105
Fair certified e-mail delivery
Communication by e-mail has become a vital part of everyday business and has replaced most of the conventional ways of communicating. Important business correspondence may require certified e-mail delivery, analogous to that provided by conventional mail service. This paper presents a novel certified e-mail delivery protocol that provides non-repudiation of origin and non-repudiation of receipt security services to protect communicating parties from each other's false denials that the e-mail has been sent and received. The protocol provides strong fairness to ensure that the recipient receives the e-mail if and only if the sender receives the receipt. The protocol makes use of an off-line and transparent trusted third party only in exceptional circumstances, i.e. when the communicating parties fail to complete the e-mail for receipt exchange due to a network failure or a party's misbehaviour. Considerations have been taken in the protocol design to reduce the use of expensive cryptographic operations for better efficiency and cost-effectiveness.
15131459
An Ant Colony Optimization Algorithm for Learning Classification Rules
Ant colony optimization (ACO) algorithm has been applied to data mining recently. Aiming at Ant Miner, a classification rule learning algorithm based on ACO, this paper presents an enhanced Ant Miner, which includes two main contributions. Firstly, a rule punishing operator is employed to reduce the number of rules and the number of conditions. Secondly, an adaptive state transition rule and a mutation operator are applied to the algorithm to speed up the convergence rate. The results of experiments on some data sets demonstrate that the enhanced Ant-Miner can quickly discover better classification rules which have roughly competitive predicative accuracy and short rules
32437026
Fuzzy Comprehensive Evaluation for Power Network Operating Schemes
Based on the analytic hierarchy process, a fuzzy comprehensive evaluation method is proposed for power network operating schemes. Performance indices and corresponding membership functions are presented to denote their contributions on overall objective. The analytic hierarchy process is used to analyze influencing factors, to establish a hierarchical model and to rank the influencing factors in order of importance. After detailed analyses and calculations for each operating scheme, quantitative evaluation results that considering various factors comprehensively are obtained by a two-level fuzzy comprehensive evaluation. A decision support system using the proposed method is developed. Simulation results of a practical power system show its validity and effectiveness.
13934101
E-learning and Its Information Technology
E-learning will be introduced as an integral part of an environment where teaching is transformed and where learning is an ongoing, creative process. In this paper, we discuss the e-learning and its technology. Our world is changing, and information and communication technology (ICT) is central to this change. Digital media has revolutionized the information society. These advances in ICT have dramatically changed the learning and teaching process, and have expanded new learning opportunities and access to educational resources beyond those traditionally available. ICT, when successfully integrated into teaching and learning, can ensure the meaningful interaction of learners with information.