Knowlog: Knowledge + Datalog for Distributed Systems

One of the new emerging trends that is gaining a lot of attentions in the database community is about distributed programming in large datacenters. A lot of discussions are arising around the CAP theorem [8] and how to achieve correct and efficient programs while performing less coordi-nated actions as possible. In order to address these issues, monotonic logic programming [4] has been employed to for-mally specify eventually consistent distributed programs. We conjecture that a missing piece in the current state-of-the-art is the capability to express statements about the knowledge state of distributed nodes, i.e., statements about what a node ”knows ” given the current system configura-tion. In fact, reasoning about the state of remote nodes is fundamental in distributed contexts in order to design and analyze protocols behavior or perform coordinated actions [10]. To reach this goal, we leverage Datalog ¬ with an epis-temic modal operator, allowing the programmer to directly express nodes ’ state of knowledge instead of low level com-munication details. As a result, reasoning about high level properties of distributed programs can be performed. To support the effectiveness of our proposal, we introduce, as example, the declarative implementation of the well-known protocol employed to execute distributed transactions: the two phase commit protocol. 1