BarQL: Collaborating Through Change

Applications such as Google Docs, Office 365, and Dropbox show a growing trend towards incorporating multi-user collaboration functionality into web applications. These collaborative applications share a need to efficiently express shared state, typically through a shared log abstraction. Extensive research efforts on log abstractions by the database, programming languages, and distributed systems communities have identified a variety of analysis techniques based on the algebraic properties of updates (i.e., pairwise commutativity, subsumption, and idempotence). Although these techniques have been applied to specific application domains, to the best of our knowledge, no attempt has been made to create a general framework for such analyses in the context of a non-trivial update language. In this paper, we introduce monadic logs, a semantically rich state abstraction that provides a powerful, expressive framework for reasoning about a variety of application state properties. We also define BarQL, a general purpose state-update language, and show how the monadic log abstraction allows us to reason about the properties of updates expressed in BarQL. Finally, we show how such analyses can be expressed declaratively using the SPARQL graph query language.