Chaining, Referral, Subscription, Leasing:
	New Mechanisms in Distributed Query Optimization
	
	Arnaud Sahuguet, Benjamin Pierce, Val Tannen

This work outlines a flexible framework for optimizing and deploying
distributed queries in wide area networks.
The database field has developed very powerful techniques for finding
efficient execution plans for declaratively specified queries.
However, applying these optimization techniques in the setting of
distributed information management requires centralized knowledge of
the entire network and assumes passive behavior from the data sources.
The reality of the Web is different. Future distributed query
optimizers must handle (in fact, exploit!) a rich variety of
information flow mechanisms like chaining, referral, proxying,
brokering, publish-subscribe, leasing, etc. We look to mobile agent
technologies for the combination of flexibility and precision needed
for handling these mechanisms.
Our language-based approach uses a mobile process calculus based on
the pi-calculus in combination with a powerful query-plan language.
The salient characteristic of the language is that messaging,
migration, and database operations all live in the same semantic space
and interact, creating new opportunities for optimization.