Entangled queries: enabling declarative data-driven coordination
Proceedings of the 2011 ACM SIGMOD International Conference on Management of data
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There are many applications that require users to coordinate and communicate. Friends want to coordinate travel plans, students want to jointly enroll in the same set of courses, and busy professionals want to coordinate their schedules. These tasks are difficult to program using existing abstractions provided by database systems because in addition to the traditional ACID properties provided by the system they all require some type of coordination between users. This is fundamentally incompatible with isolation in the classical ACID properties of transactions. In this talk, I argue that it is time for the database and event processing communities to look beyond isolation towards principled and elegant abstractions that allow for communication and coordination between some notion of (suitably generalized) transactions. This new area of declarative data-driven coordination (D3C) is motivated by many novel applications and is full of challenging research problems. I will start by surveying existing abstractions in database systems and explain why they are insufficient for D3C. I will then describe entangled queries, a coordination language that extends SQL by constraints that allow for the co-ordinated choice of result tuples across queries originating from different users or applications, and I will discuss algorithms for evaluating entangled queries. I will conclude with a set of research challenges for event processing in this new area.