Building Dynamic Market Places Using HyperQueries
Lecture Notes in Computer Science
Motivation and Introduction Electronic market places and virtual enterprises have become important applications for query processing  . Building a scalable virtual B2B market place with hundreds or thousands participants requires highly flexible, distributed query processing capabilities. Architecting an electronic market place as a data warehouse by integrating all the data from all participating enterprises in one centralized data repository incurs severe problems: -Security and privacy
... lations: The participants of the market place have to relinquish the control over their data and entrust sensitive information to the market place host. -Coherence problems: The coherence of highly dynamic data, such as availability and shipping information, may be violated due to outdated materialized data in the market place's data warehouse. -Schema integration problems: Using the warehouse approach all relevant data from all participants have to be convertedà priori into the same format. Often, it would be easier to leave the data inside the participant's information systems, e.g., legacy systems, within the local sites, and apply particular local wrapper operations. This way, data is only converted on demand and the most recent coherent state of the data is returned. -Fixed query operators: In a data warehouse-like electronic market place, all information is converted into materialized data. This is often not desirable in such complex applications like electronic procurement/bidding. We propose a reference architecture for building scalable and dynamic market places and a framework for evaluating so-called HyperQueries in such an environment. HyperQueries are essentially query evaluation sub-plans "sitting behind" hyperlinks. This way the electronic market place can be built as an intermediary between the client and the providers executing their sub-queries referenced via hyperlinks. The hyperlinks are embedded as attribute values within data objects of the intermediary's database (Figure 1(a) ). Retrieving such a virtual object automatically initiates the execution of the referenced HyperQuery in order to materialize the entire object.