When Can We Answer Queries Using Result-Bounded Data Interfaces?

TL;DR

This paper investigates the conditions under which queries can be answered using result-bounded data interfaces, focusing on answerability, plan computation, and the impact of data constraints.

Contribution

It introduces a framework for determining query answerability with result-bounded methods, including reduction to query containment and schema simplification theorems.

Findings

Answerability reduces to query containment with constraints.

Schema simplification theorems clarify when result-bounded services are usable.

Decidability and complexity results are provided for common constraints.

Abstract

We consider answering queries on data available through access methods, that provide lookup access to the tuples matching a given binding. Such interfaces are common on the Web; further, they often have bounds on how many results they can return, e.g., because of pagination or rate limits. We thus study result-bounded methods, which may return only a limited number of tuples. We study how to decide if a query is answerable using result-bounded methods, i.e., how to compute a plan that returns all answers to the query using the methods, assuming that the underlying data satisfies some integrity constraints. We first show how to reduce answerability to a query containment problem with constraints. Second, we show "schema simplification" theorems describing when and how result-bounded services can be used. Finally, we use these theorems to give decidability and complexity results about answerability for common constraint classes.