Querying contract databases based on temporal behavior.

Considering a broad definition for service contracts (beyond web services and software, e.g. airline tickets and insurance policies), we tackle the challenges of building a high performance broker in which contracts are both specified and queried through their temporal behavior. The temporal dimension, in conjunction with traditional relational attributes, enables our system to better address difficulties arising from the great deal of information regarding the temporal interaction of the various events cited in contracts (e.g. "No refunds are allowed after a reschedule of the flight, which can be requested only before any flight leg has been used"). On the other hand, querying large repositories of temporal specifications poses an interesting indexing challenge. In this paper, we introduce two distinct and complementary indexing techniques that enable our system to scale the evaluation of a novel and theoretically sound notion of permission of a temporal query by a service contract. Our notion of permission is inspired by previous work on model checking but, given the specific characteristic of our problem, does not reduce to it. We evaluate experimentally our implementation, showing that it scales well with both the number and the complexity of the contracts.