FC-Datalog as a Framework for Efficient String Querying

TL;DR

This paper introduces FC-Datalog, a recursive logic framework for efficient string querying that captures core spanners, offering a range of fragments optimized for different complexity and application needs.

Contribution

It extends FC with recursion to define core spanners, introduces fragments with desirable complexity properties, and demonstrates simulation of regex within this framework.

Findings

Fragments capturing LOGSPACE complexity

Linear combined complexity fragments

Simulation of deterministic regex in FC-Datalog

Abstract

Core spanners are a class of document spanners that capture the core functionality of IBM's AQL. FC is a logic on strings built around word equations that when extended with constraints for regular languages can be seen as a logic for core spanners. The recently introduced FC-Datalog extends FC with recursion, which allows us to define recursive relations for core spanners. Additionally, as FC-Datalog captures P, it is also a tractable version of Datalog on strings. This presents an opportunity for optimization. We propose a series of FC-Datalog fragments with desirable properties in terms of complexity of model checking, expressive power, and efficiency of checking membership in the fragment. This leads to a range of fragments that all capture LOGSPACE, which we further restrict to obtain linear combined complexity. This gives us a framework to tailor fragments for particular applications. To showcase this, we simulate deterministic regex in a tailored fragment of FC-Datalog.