Relational transducers for declarative networking

TL;DR

This paper introduces a formal model for distributed querying in declarative networking using relational transducers, establishing a connection between coordination-freeness and monotonicity of queries, and characterizing their computational power.

Contribution

It defines coordination-freeness for transducer networks and proves it precisely captures monotone queries, linking semantic and syntactic properties in distributed computation.

Findings

Coordination-free transducer networks exactly capture monotone queries.

Oblivious transducers syntactically characterize coordination-free computations.

Non-coordination-free transducers are significantly more powerful.

Abstract

Motivated by a recent conjecture concerning the expressiveness of declarative networking, we propose a formal computation model for "eventually consistent" distributed querying, based on relational transducers. A tight link has been conjectured between coordination-freeness of computations, and monotonicity of the queries expressed by such computations. Indeed, we propose a formal definition of coordination-freeness and confirm that the class of monotone queries is captured by coordination-free transducer networks. Coordination-freeness is a semantic property, but the syntactic class that we define of "oblivious" transducers also captures the same class of monotone queries. Transducer networks that are not coordination-free are much more powerful.