A differential refresh scheme for remote end-user\u27s views

The growth of end-user computing and recent developments in information technology, such as client/server architecture and data warehouse, promote the use of remote materialized views (RMVs) to support end-users. This article presents a differential scheme to refresh remote end-user\u27s views. The scheme stores the effects of updates relevant to the RMV in a difference table which is transmitted to the remote site upon receiving the refresh request to update the RMV. The scheme provides a fast response to a user\u27s refresh request. We discuss the data structures and algorithms of the scheme. Performance measures are developed and compared with the regeneration scheme

Active Ontology: An Information Integration Approach for Dynamic Information Sources

In this paper we describe an ontology-based information integration approach that is suitable for highly dynamic distributed information sources, such as those available in Grid systems. The main challenges addressed are: 1) information changes frequently and information requests have to be answered quickly in order to provide up-to-date information; and 2) the most suitable information sources have to be selected from a set of different distributed ones that can provide the information needed. To deal with the first challenge we use an information cache that works with an update-on-demand policy. To deal with the second we add an information source selection step to the usual architecture used for ontology-based information integration. To illustrate our approach, we have developed an information service that aggregates metadata available in hundreds of information services of the EGEE Grid infrastructure

ENHANCING DATABASE PERFORMANCE IN A DSS ENVIRONMENT VIA QUERY CACHING

A key element in all decision support systems is availability of sufficiently good and timely data to support the decision making process. Much research was, and is, devoted to data and information quality: attributes, assurance that quality data is used in the decision process, etc. In this paper we concentrate on a particular dimension of data availability and usage -the retrieval of data in a timely and decision enhancing manner. We propose to augment the decision support databases by an adaptive and efficient query cache. The cache contains snapshots of the decision support database, each being the answer to a recently invoked query. A snapshot can be reused by the originating user, or a different user, at a later time --provided the use of cached data leads to savings over the use of a new query, and these savings exceed the cost of using stale date. The proposed scheme is conceptually different from conventional data replication schemes. In data replication schemes the data items to be replicated and the protocols for concurrency control are defined at the system level. In our scheme the cache is populated dynamically and the snapshots it contains are refreshed only if the cost of using stale information is higher than cost of refreshing the snapshots. At the same time, users can still decide to refresh the stored snapshot, based on their own decision environment. Our scheme thus enhances the data retrievalprocess, while supporting a more efficient data retrieval at both the user level and the data warehouse leve