International Journal of Web Information Systems

Enforcing data consistency in data integration systems by XQuery trigger service : Table of Contents

Jing Lu, Bernhard Mitschang — Sun Jun 07 14:15:03 BST 2009

Abstract:
Purpose – Extensible Markup Language (XML)-based data integration systems (DIS) aim to support global updates. Data consistency among data sources is not yet enforced at the integration level or enforced in an ad hoc manner which leads to redundant checking of consistency or unrepairable mistakes. This paper aims to provide XQuery trigger service to enforce data integrity and data consistency in the DIS at the integration level. Design/methodology/approach – Data consistency is enforced among data sources through providing XQuery trigger service for the XML-DIS. An XQuery trigger model is defined and shown how to use this model to define different integrity constraints and triggers at the integration level. The paper proposes the architecture of the XQuery trigger service and shows how to enforce data consistency in the DIS. Important components including event detection, condition evaluation and action firing are discussed. Necessary algorithms including how to produce ChangeRecord, how to find activated triggers, how to process LET and FOR clauses and how to create data objects from XML fragment are proposed. Trigger termination and failure handling are also discussed. Findings – XQuery trigger can express miscellaneous data integrity constraints and triggers in the DIS and is highly abstract, refined and easy to understand. XQuery trigger service provides an easy-to-maintain method of the data consistency rules and a uniform, nonredundant and centralized enforcement of data consistency. Originality/value – An XQuery trigger model with namespace annotations, which can define constraints and triggers among different data sources. An XQuery trigger service architecture for the XML-DIS, which can enforce data consistency at the integration level. For DIS administrators, who want to enforce data consistency when permitting updates at the integration level.

Web ontology data matching for integration: method and framework : Table of Contents

Chao Wang, Jie Lu, Guangquan Zhang — Sun Jun 07 14:15:03 BST 2009

Abstract:
Purpose – Matching relevant ontology data for integration is vitally important as the amount of ontology data increases along with the evolving Semantic web, in which data are published from different individuals or organizations in a decentralized environment. For any domain that has developed a suitable ontology, its ontology annotated data (or simply ontology data) from different sources often overlaps and needs to be integrated. The purpose of this paper is to develop intelligent web ontology data matching method and framework for data integration. Design/methodology/approach – This paper develops an intelligent matching method to solve the issue of ontology data matching. Based on the matching method, it also proposes a flexible peer-to-peer framework to address the issue of ontology data integration in a distributed Semantic web environment. Findings – The proposed matching method is different from existing data matching or merging methods applied to data warehouse in that it employs a machine learning approach and more similarity measurements by exploring ontology features. Research limitations/implications – The proposed method and framework will be further tested for some more complicated real cases in the future. Originality/value – The experiments show that this proposed intelligent matching method increases ontology data matching accuracy.

Providing internet connectivity and mobility management for MANETs : Table of Contents

Sun Jun 07 14:15:03 BST 2009

Abstract:
Purpose – The purpose of this paper is to describe the required functionalities on providing internet connectivity and mobility management for mobile ad hoc networks (MANETs), present discovered problems such as inconsistent contexts, and provide the corresponding solutions. It also provides a hybrid metric for the load-balance of intra/inter-MANET traffic over multiple internet gateways (IGWs). Design/methodology/approach – The paper uses both mathematical analyses and simulations to discover the required functionalities and problems on providing internet connectivity and mobility management for MANETs. The proposed hybrid metric for IGW selection is a replacement of the shortest hop-count (HC) metric, and consider three factors: HC distance, intra-MANET traffic, and inter-MANET traffic. Findings – Simulation results show that ad hoc routing protocols, using the proposed metric, get better performance in terms of packet delivery ratio and transmission delay, at the cost of slightly increased signalling overhead. Research limitations/implications – In the assessment, simulation results are taken from two mobility scenarios, and the hybrid metric is integrated into only reactive ad hoc routing. Thus, more case studies need to be carried out to demonstrate the outcomes of the proposed metric compared with others. Practical implications – This paper provides the needed functionalities for broadening the richness of MANET applications to internet users, and vice verse. Originality/value – This paper contributes to the research on internetworking and mobility management between MANETs and the internet.

Algorithms for structure-based grouping in XML-OLAP : Table of Contents

Chantola Kit, Toshiyuki Amagasa, Hiroyuki Kitagawa — Sun Jun 07 14:15:03 BST 2009

Abstract:
Purpose – The purpose of this paper is to propose efficient algorithms for structural grouping over Extensible Markup Language (XML) data, called TOPOLOGICAL ROLLUP (T-ROLLUP), which are to compute aggregation functions based on XML data with multiple hierarchical levels. They play important roles in the online analytical processing of XML data, called XML-OLAP, with which complex analysis over XML can be performed to discover valuable information from XML. Design/methodology/approach – Several variations of algorithms are proposed for efficient T-ROLLUP computation. First, two basic algorithms, top-down algorithm (TDA) and bottom-up algorithm (BUA), are presented in which the well-known structural-join algorithms are used. The paper then proposes more efficient algorithms, called single-scan by preorder number and single-scan by postorder number (SSC-Pre/Post), which are also based on structural joins, but have been modified from the basic algorithms so that multiple levels of grouping are computed with a single scan over node lists. In addition, the paper attempts to adopt the algorithm for parallel execution in multi-core environments. Findings – Several experiments are conducted with XMark and synthetic XML data to show the effectiveness of the proposed algorithms. The experiments show that proposed algorithms perform much better than the naïve implementation. In particular, the proposed SSC-Pre and SSC-Post perform better than TDA and BUA for all cases. Beyond that, the experiment using the parallel single scan algorithm also shows better performance than the ordinary basic algorithm. Research limitations/implications – This paper focuses on the T-ROLLUP operation for XML data analysis. For this reason, other operations related to XML-OLAP, such as CUBE, WINDOWING, and RANKING should also be investigated. Originality/value – The paper presents an extended version of one of the award winning papers at iiWAS2008.

XML data partitioning schemes for parallel holistic twig joins : Table of Contents

Imam Machdi, Toshiyuki Amagasa, Hiroyuki Kitagawa — Sun Jun 07 14:15:03 BST 2009

Abstract:
Purpose – The purpose of this paper is to propose Extensible Markup Language (XML) data partitioning schemes that can cope with static and dynamic allocation for parallel holistic twig joins: grid metadata model for XML (GMX) and streams-based partitioning method for XML (SPX). Design/methodology/approach – GMX exploits the relationships between XML documents and query patterns to perform workload-aware partitioning of XML data. Specifically, the paper constructs a two-dimensional model with a document dimension and a query dimension in which each object in a dimension is composed from XML metadata related to the dimension. GMX provides a set of XML data partitioning methods that include document clustering, query clustering, document-based refinement, query-based refinement, and query-path refinement, thereby enabling XML data partitioning based on the static information of XML metadata. In contrast, SPX explores the structural relationships of query elements and a range-containment property of XML streams to generate partitions and allocate them to cluster nodes on-the-fly. Findings – GMX provides several salient features: a set of partition granularities that balance workloads of query processing costs among cluster nodes statically; inter-query parallelism as well as intra-query parallelism at multiple extents; and better parallel query performance when all estimated queries are executed simultaneously to meet their probability of query occurrences in the system. SPX also offers the following features: minimal computation time to generate partitions; balancing skewed workloads dynamically on the system; producing higher intra-query parallelism; and gaining better parallel query performance. Research limitations/implications – The current status of the proposed XML data partitioning schemes does not take into account XML data updates, e.g. new XML documents and query pattern changes submitted by users on the system. Practical implications – Note that effectiveness of the XML data partitioning schemes mainly relies on the accuracy of the cost model to estimate query processing costs. The cost model must be adjusted to reflect characteristics of a system platform used in the implementation. Originality/value – This paper proposes novel schemes of conducting XML data partitioning to achieve both static and dynamic workload balance.