Generalized Core Spanner Inexpressibility via Ehrenfeucht-Fra\"iss\'e Games for FC

TL;DR

This paper uses Ehrenfeucht-Fra"issé games to establish inexpressibility results for the logic FC, revealing limitations of generalized core spanners in capturing certain relations, and providing new insights into their expressive power.

Contribution

It introduces inexpressibility lemmas for FC using Ehrenfeucht-Fra"issé games and applies them to demonstrate the limitations of generalized core spanners.

Findings

Several relations cannot be selected by generalized core spanners

Inexpressibility lemmas effectively demonstrate expressive limitations

Provides new insights into the expressive power of core spanners

Abstract

Despite considerable research on document spanners, little is known about the expressive power of generalized core spanners. In this paper, we use Ehrenfeucht-Fra\"iss\'e games to obtain general inexpressibility lemmas for the logic FC (a finite-model variant of the theory of concatenation). Applying these lemmas give inexpressibility results for FC that we lift to generalized core spanners. In particular, we give several relations that cannot be selected by generalized core spanners, thus demonstrating the effectiveness of the inexpressibility lemmas. As an immediate consequence, we also gain new insights into the expressive power of core spanners.