Expressiveness within Sequence Datalog

TL;DR

This paper explores the expressive power of Sequence Datalog by analyzing various features like negation, recursion, and path equations, establishing a comprehensive hierarchy of their relative capabilities.

Contribution

It provides a complete characterization of the expressiveness relationships among Sequence Datalog features, including new features like equations and packing.

Findings

Certain features are redundant and can be expressed with others.

A hierarchy of expressiveness among Sequence Datalog fragments is established.

The results clarify the minimal feature sets needed for specific sequence query capabilities.

Abstract

Motivated by old and new applications, we investigate Datalog as a language for sequence databases. We reconsider classical features of Datalog programs, such as negation, recursion, intermediate predicates, and relations of higher arities. We also consider new features that are useful for sequences, notably, equations between path expressions, and "packing". Our goal is to clarify the relative expressiveness of all these different features, in the context of sequences. Towards our goal, we establish a number of redundancy and primitivity results, showing that certain features can, or cannot, be expressed in terms of other features. These results paint a complete picture of the expressiveness relationships among all possible Sequence Datalog fragments that can be formed using the six features that we consider.