Document SQL (DSQL)

This chapter presents DSQL, a conservative extension of SQL, as an ad-hoc query language for XML. The development of DSQL follows the theoretical foundations of first order logic, and uses common query semantics already accepted for SQL. DSQL represents a core subset of XQuery that lends well to query optimization techniques; while at the same time allows easy integration into current databases and applications that use SQL. The intent of DSQL is not to replace XQuery, the current W3C recommended XML query language, but to serve as an ad-hoc querying frontend to XQuery. Further, the authors present proofs for important query language properties such as complexity and closure. An empirical study comparing DSQL and XQuery for the purpose of ad-hoc querying demonstrates that users perform better with DSQL for both flat and tree structures, in terms of both accuracy and efficiency.

Cost Modeling and Range Estimation for Top-k Retrieval in Relational Databases

Relational databases have increasingly become the basis for a wide range of applications that require efficient methods for exploratory search and retrieval. Top-k retrieval addresses this need and involves finding a limited number of records whose attribute values are the closest to those specified in a query. One of the approaches in the recent literature is query-mapping which deals with converting top-k queries into equivalent range queries that relational database management systems (RDBMSs) normally support. This approach combines the advantages of simplicity as well as practicality by avoiding the need for modifications to the query engine, or specialized data structures and indexing techniques to handle top-k queries separately. This paper reviews existing query-mapping techniques in the literature and presents a range query estimation method based on cost modeling. Experiments on real world and synthetic data sets show that the cost-based range estimation method performs at least as well as prior methods and avoids the need to calibrate workloads on specific database contents.

XTEngine

There has been extensive research in XML Keyword-based and Loosely Structured querying. Some frameworks work well for certain types of XML data models while fail in others. The reason is that the proposed techniques overlook the context of elements when building relationships between the elements. The context of a data element is determined by its parent, because a data element is generally a characteristic of its parent. Overlooking the contexts of elements may result in relationships between the elements that are semantically disconnected, which lead to erroneous results. We present in this chapter a context-driven search engine called XTEngine for answering XML Keyword-based and Loosely Structured queries. XTEngine treats each set of elements consisting of a parent and its children data elements as one unified entity, and then uses context-driven search techniques for determining the relationships between the different unified entities. We evaluated XTEngine experimentally and compared it with three other search engines. The results showed marked improvement.

Towards Autonomic Workload Management in DBMSs

Workload management is the discipline of effectively managing, controlling and monitoring work flow across computing systems. It is an increasingly important requirement of database management systems (DBMSs) in view of the trends towards server consolidation and more diverse workloads. Workload management is necessary so the DBMS can be business-objective oriented, can provide efficient differentiated service at fine granularity and can maintain high utilization of resources with low management costs. We see that workload management is shifting from offline planning to online adaptation. In this paper we discuss the objectives of workload management in autonomic DBMSs and provide a framework for examining how current workload management mechanisms match up with these objectives. We then use the framework to study several mechanisms from both DBMS products and research efforts. We also propose directions for future work in the area of workload management for autonomic DBMSs.

General Strategy for Querying Web Sources in a Data Federation Environment

Modern database management systems are supporting the inclusion and querying of non-relational sources within a data federation environment via wrappers. Wrapper development for Web sources, however, is a convolution of code with extraction and query planning knowledge and becomes a daunting task. We use IBM DB2 federation engine to demonstrate the challenges of incorporating web sources into a data federation. We, then, present a practical and general strategy for the inclusion and querying of web sources without requiring any changes in the underlying data federation technology. This strategy separates the code and knowledge in wrapper development by introducing a general-purpose capabilities-aware mini query-planner and a data extraction engine. As a result, Web sources can be included in a data federation system faster, and maintained easier.

On Efficient Evaluation of XML Queries

Recently, the use of XML continues to grow in popularity, large repositories of XML documents are going to emerge, and users are likely to pose increasingly more complex queries on these data sets. In 2001 XQuery is decided by the World Wide Web Consortium (W3C) as the standard XML query language. In this article, we describe the design and implementation of an efficient and scalable purely relational XQuery processor which translates expressions of the XQuery language into their equivalent SQL evaluation scripts. The experiments of this article demonstrated the efficiency and scalability of our purely relational approach in comparison to the native XML/XQuery functionality supported by conventional RDBMSs and has shown that our purely relational approach for implementing XQuery processor deserves to be pursued further.

Scalable XML Filtering for Content Subscriptions

Over the past few years, there have been an increasing number of Web applications that exchange various types of data on the Internet. In this article, we propose a technique for building efficient and scalable XML publish/subscribe applications. In particular, we look at the problem of processing streaming XML data efficiently against a large number of branch XPath queries. To improve the performance of XML data processing, the branch queries that have similar query characteristics are grouped, and common paths between the queries in the same group are identified. Then, these groups of queries are processed against an XML schema to validate query structures. After performing structural matching of queries, the queries are organized in a way that multiple queries can be evaluated simultaneously in the post-processing phase. In the post-processing phase, join operations are executed in a pipeline fashion, and intermediate join results are shared amongst the queries in the same group. The benefit of this approach is that, the total number of join operations performed in the post-processing phase is significantly reduced. In addition, we also present how to efficiently return all matching elements for each matching branch query. Experiments show that our proposal is efficient and scalable compared to previous works.

Ontology Based Object-Oriented Domain Modeling

An important step in developing the requirements for an information system is analyzing the application domain. In this step, conceptual models are used for representing an application domain. However, while languages for software design are available and widely used, no generally accepted language exists for conceptual modeling. This work suggests the use of object-oriented software modeling languages also for conceptual modeling. Such use can support a more accurate transition from domain modes to software models. As software-modeling languages were not intended for modeling application domains, their constructs lack the required semantics. While previous papers addressed the representation of structural elements of domains using object concepts, this paper addresses behavioral aspects, related to change and interaction. The proposed semantics are based on a mapping between ontological concepts that describe behavior and object-oriented constructs related to dynamics. Based on these mappings, modeling rules are proposed to guide the modeler in creating ontologically well-formed models. The mappings and rules are exemplified using UML and are demonstrated using a case study.

Visual Support for Use Case Modeling

The Unified Modeling Language (UML) has been evolving as a standard approach to Systems Analysis and Design. Use cases are a de facto standard tool, and corresponding use case diagrams offer visual support for this tool. The Cognitive Theory of Multimedia Learning suggests that the visual nature of use case diagrams would enhance understanding, particularly for novice users, by providing visual cues to focus relevant information. This paper describes an experiment to test this theory, offering use cases with and without supporting use case diagrams. Retention, comprehension, and problem solving tasks were tested and measured. As hypothesized, the results find that users had a significantly higher level of understanding, measured by problem solving tasks, if they were provided with use case diagrams accompanying the use cases. These results are promising support that use cases and use case diagrams could be considered important boundary objects in systems analysis.

Towards Structured Flexibility in Information Systems Development

Method configuration is a specific type of Method Engineering (ME) that takes an existing organization-wide Information Systems Development Method (ISDM) as its point of departure. Existing assembly-based ME approaches are not well suited to this task. As an alternative, this paper suggests a metamethod approach to tailoring organization-wide ISDMs. We refer to this approach as the Method for Method Configuration (MMC). MMC takes into account the need to combine structure, which is one reason for choosing an organization-wide ISDM in the first place, with flexibility, which is essential for making the chosen ISDM fit actual projects. The metamethod is built using a three-layered reuse model comprising method components, configuration packages, and configuration templates. These concepts are combined efficiently to produce a situational method and thereby to facilitate the work of method engineers.