In this paper we introduce the concept of continual queries, describe the design of a distributed event-driven continual query system -- OpenCQ, and outline the initial implementation of OpenCQ on top of the distributed interoperable information mediation system DIOM [21, 19]. Continual queries are standing queries that monitor update of interest and return results whenever the update reaches specified thresholds. In OpenCQ, users may specify to the system the information they would like to monitor (such as the events or the update thresholds they are interested in). Whenever the information of interest becomes available, the system immediately delivers it to the relevant users; otherwise, the system continually monitors the arrival of the desired information and pushes it to the relevant users as it meets the specified update thresholds. In contrast to conventional pull-based data management systems such as DBMSs and Web search engines, OpenCQ exhibits two important featu...

Abstract | Accessing many data sources aggravates problems for users of heterogeneous distributed databases. Database administrators must deal with fragile mediators, that is, mediators with schemas and views that must be signi cantly changed to incorporate a new data source. When implementing translators of queries from mediators to data sources, database implementors must deal with data sources that do not support all the functionality required by mediators. Application programmers must deal with graceless failures for unavailable data sources. Queries simply return failure and no further information when data sources are unavailable for query processing. The Distributed Information Search COmponent (Disco) addresses these problems. Data modeling techniques manage the connections to data sources, and sources can be added transparently to the users and applications. The interface between mediators and data sources exibly handles di erent query languages and different data source functionality. Query rewriting and optimization techniques rewrite queries so they are e ciently evaluated by sources. Query processing and evaluation semantics are developed to process queries over unavailable data sources. In this article we describe (a) the distributed mediator architecture of Disco � (b) the data model and its modeling of data source connections � (c) the interface to underlying data sources and the query rewriting process � and (d) query processing semantics. We describe several advantages of our system.

Recently, there has been a great deal of research into XML query languages to enable the execution of database-style queries over XML files. However, merely being an XML query-processing engine does not render a system suitable for querying the Internet. A useful system must provide mechanisms to (a) find the XML files that are relevant to a given query, and (b) deal with remote data sources that either provide unpredictable data access and transfer rates, or are infinite streams, or both. The Niagara Internet Query System was designed from the bottom-up to provide these mechanisms. In this article we describe the overall Niagara architecture, and how Niagara finds relevant XML documents by using a collaboration between the Niagara XML-QL query processor and the Niagara “text-in-context ” XML search engine. The Niagara Internet Query System is public domain software that can be found at

The dQUOB system satisfies client need for specific information from high-volume data streams. The data streams we speak of are the flow of data existing during large-scale visualizations, video streaming to large numbers of distributed users, and high volume business transactions. We introduces the notion of conceptualizing a data stream as a set of relational database tables so that a scientist can request information with an SQL-like query. Transformation or computation that often needs to be performed on the data en-route can be conceptualized ascomputation performed on consecutive views of the data, with computation associated with each view. The dQUOB system moves the query code into the data stream as a quoblet; as compiled code. The relational database data model has the significant advantage of presenting opportunities for efficient reoptimizations of queries and sets of queries. Using examples from global atmospheric modeling, we illustrate the usefulness of the dQUOB system. We carry the examples through the experiments to establish the viability of the approach for high performance computing with a baseline benchmark. We define a cost-metric of end-to-end latency that can be used to determine realistic cases where optimization should be applied. Finally, we show that end-to-end latency can be controlled through a probability assigned to a query that a query will evaluate to true.

The World Wide Web (the Web) has made an enormous amount of data freely accessible over the Internet. However, finding the right information in the midst of this mountain of data has been likened to finding the proverbial needle in a haystack. Commonly used search engines (e.g., AltaVista) and directory services (e.g., Yahoo) have practical but limited success. The exponential growth of the Web is increasing the haystack rapidly. Instead of pull-based browsing, update monitoring is a promising area of research where the system brings the right information to the right user at the right time. In this paper we present the design and implementation of the Conquer continual query system, designed for update monitoring over the Web information sources. A Continual Query (CQ) is a standing query that monitors update of interest using distributed triggers and notifies the user of changes whenever an update of interest reaches specified thresholds or some time limit is reached. In co...

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We propose a query mediation framework to support customizable information gathering across heterogeneous and autonomous information sources. Instead of an integrated (and static) global schema, we propose an adaptive approach to interoperability which allows information consumers to represent their queries based on the customized personal view rather than a system-defined integrated view. The query mediation framework consists of five steps: query routing, query decomposition, parallel access plan generation, subquery translation and execution, and query result assembly. Concrete examples illustrate the challenges arising from heterogeneity in these five steps and how the framework scales up as the number of information sources grow and evolve. 1 Introduction Large-scale cooperative information systems often require information consumers and information producers to cooperate across departmental, organizational, and national boundaries. The goal of cooperation is to increase producti...

Introduction The World Wide Web (WWW) made an unprecedented amount and variety of data accessible to all Internet users. However, users suffer from information starvation under this data overload, due to the daunting challenge of navigating, collecting, evaluating, and processing data in this dynamic and open information universe. The problem is aggravated when information changes constantly, but unpredictably. For example, as more aspects of business and commerce migrate online, system-supported update monitoring and event-driven information delivery becomes increasingly important because it reduces the time users spend hunting for the updated information as well as unnecessary traffic on the net. The CQ project at OGI, funded by DARPA, aims at developing a scalable toolkit and techniques for update monitoring and event-driven information delivery on the net. The main feature of the CQ project is a "personalized update monitoring" toolkit based on continual queries<F2

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A major problem today is that important data is scattered throughout dozens of separately evolved data sources, in a form that makes the "big picture" difficult to obtain. Data integration presents a unified virtual view of all data within a domain, allowing the user to pose queries across the complete integrated schema. This dissertation addresses the performance needs...