Compressed Representations of Conjunctive Query Results

TL;DR

This paper introduces a space-efficient, tunable data structure for compressing conjunctive query results, enabling faster access and reduced storage, tailored to query structure and access patterns.

Contribution

It presents a novel parameterized data structure that balances space and answer time, supporting efficient representation of conjunctive query outputs.

Findings

Supports efficient access to compressed query results

Allows precise control of space versus answer time tradeoff

Applicable to various classes of conjunctive queries

Abstract

Relational queries, and in particular join queries, often generate large output results when executed over a huge dataset. In such cases, it is often infeasible to store the whole materialized output if we plan to reuse it further down a data processing pipeline. Motivated by this problem, we study the construction of space-efficient compressed representations of the output of conjunctive queries, with the goal of supporting the efficient access of the intermediate compressed result for a given access pattern. In particular, we initiate the study of an important tradeoff: minimizing the space necessary to store the compressed result, versus minimizing the answer time and delay for an access request over the result. Our main contribution is a novel parameterized data structure, which can be tuned to trade off space for answer time. The tradeoff allows us to control the space requirement of the data structure precisely, and depends both on the structure of the query and the access pattern. We show how we can use the data structure in conjunction with query decomposition techniques, in order to efficiently represent the outputs for several classes of conjunctive queries.