Unprecedented amounts of multidimensional array data are currently being generated in many fields. These multidimensional array data naturally and efficiently fit into the array data model, and many array management systems based on the array data model have appeared. Accordingly, the requirement for data exploration methods for large multidimensional array data has also increased. In this paper, we propose a method for efficient top- k subarray query processing in array databases, which is one of the most important query types for exploring multidimensional data. First, we define novel top- k query models for array databases: overlap-allowing and disjoint top- k subarray queries. Second, we propose a suite of top- k subarray query processing methods, called PPTS and extend them to distributed processing. Finally, we present the results of extensive experiments using real datasets from an array database, which show that our proposed methods outperform existing naïve methods.

In this paper, we propose a new method for keyword search over large graph-structured data to find a set of answers which are not only relevant to the query but also reduced and duplication-free.We define an effective answer structure and a relevance measure for the candidate answers to a keyword query on graph data.We suggest an efficient indexing scheme on relevant and useful paths from nodes to keywords in the graph.We present a top-k query processing algorithm to find relevant and non-redundant answers in an efficient way by exploiting preconstructed indexes.We show by experiments using real datasets that the proposed approach can produce effective and nonredundant answers efficiently compared to the previous methods.

In this paper, we propose an energy and latency efficient XML dissemination scheme for the mobile computing. We define a novel unit structure called G-node for streaming XML data in the wireless environment. It exploits the benefits of the structure indexing and attribute summarization that can integrate relevant XML elements into a group. It provides a way for selective access of their attribute values and text content. We also propose a lightweight and effective encoding scheme, called Lineage Encoding, to support evaluation of predicates and twig pattern queries over the stream. The Lineage Encoding scheme represents the parent-child relationships among XML elements as a sequence of bit-strings, called Lineage Code(V, H), and provides basic operators and functions for effective twig pattern query processing at mobile clients. Extensive experiments using real and synthetic data sets demonstrate our scheme outperforms conventional wireless XML broadcasting methods for simple path queries as well as complex twig pattern queries with predicate conditions.

In this article, we address the problem of delayed query processing raised by tree-based index structures in wireless broadcast environments, which increases the access time of mobile clients. We propose a novel distributed index structure and a clustering strategy for streaming XML data that enables energy and latencyefficient broadcasting of XML data. We first define the DIX node structure to implement a fully distributed index structure which contains the tag name, attributes, and text content of an element, as well as its corresponding indices. By exploiting the index information in the DIX node stream, a mobile client can access the stream with shorter latency. We also suggest a method of clustering DIX nodes in the stream, which can further enhance the performance of query processing in the mobile clients. Through extensive experiments, we demonstrate that our approach is effective for wireless broadcasting of XML data and outperforms the previous methods.

This paper presents a system architecture and information retrieval strategy for multimedia content which exploits descriptive metadata as well as domain ontology. We propose a query processing model including a semantic ranking scheme which can retrieve multimedia objects semantically relevant to the user query and provide users with a search result categorized by concepts and ordered by their semantic relevance to the query. By experiments on a prototype system using a repository of broadcast TV programs, we show effectiveness of the ontology-based multimedia search approach proposed in the paper.

OLAP queries involve a lot of aggregations on a large amount of data in data warehouses. To process expensive OLAP queries efficiently, we propose a new method for rewriting a given OLAP query using the various kinds of materialized aggregate views which already exist in data warehouses. We first define the normal forms of OLAP queries and materialized views based on the lattice of dimension hierarchies and the semantic information in data warehouses. Conditions for the usability of a materialized view in rewriting a given query are specified by relationships between the components of their normal forms. We present a rewriting algorithm for OLAP queries that effectively utilizes existing materialized views. The proposed algorithm can make use of materialized views having different selection granularities, selection regions and aggregation granularities together, to generate an efficient rewritten query.

Data replication is often considered in distributed database systems to enhance availability and performance. The benefit of data replication, however can only be realized at the cost of maintaining the consistency of data. In particular, network partition failures make it more difficult to achieve high data availability while ensuring strong correctness criteria such as l-copy serializability. We propose a replica control method to improve the availability of data in the presence of network partition failures. Our method extends the traditional primary copy method by using the relaxed correctness criterion called insular consistency for large-scale distributed systems, where partition failures frequently occur. We focus on increasing the availability of data for read-only transactions. We introduce a version vector as a tool for guaranteeing insular consistency and present a mechanism that allows read-only transactions to be executed at any partition as long as the insular consistency is satisfied. An asynchronous update propagation mechanism is also employed to improve the performance of update operations. We also show that the proposed method is correct and give some performance considerations.