Query Brokers for Distributed and Flexible Query Evaluation

This paper presents our work on supporting flexible query evaluation over large distributed, heterogeneous, and autonomous sources. Flexibility means that the query evaluation process can be configured according to application contextspecific, resources constraints and also can interact with its execution environment. Our query evaluation is based on Query Brokers as basic units which allow the query processing to interact with its environment. Queries are evaluated under query brokers contexts defining constraints of the evaluation task. Query Brokers have dynamic behaviors towards their execution environment. This paper focuses on the definition and the role of query brokers in the query evaluation task in large-scale mediation systems. We show also how query brokers ensure the flexibility of this task.