A Compact Index for Order-Preserving Pattern Matching

TL;DR

This paper introduces a space-efficient index for order-preserving pattern matching that enables fast searches by decomposing sequences into order and delta components, outperforming existing methods.

Contribution

It presents a novel, practical index for offline order-preserving pattern matching that balances small space usage with high retrieval speed.

Findings

Faster than existing alternatives in experiments

Uses less space while maintaining efficiency

First approach to combine small space and fast retrieval

Abstract

Order-preserving pattern matching was introduced recently but it has already attracted much attention. Given a reference sequence and a pattern, we want to locate all substrings of the reference sequence whose elements have the same relative order as the pattern elements. For this problem we consider the offline version in which we build an index for the reference sequence so that subsequent searches can be completed very efficiently. We propose a space-efficient index that works well in practice despite its lack of good worst-case time bounds. Our solution is based on the new approach of decomposing the indexed sequence into an order component, containing ordering information, and a delta component, containing information on the absolute values. Experiments show that this approach is viable, faster than the available alternatives, and it is the first one offering simultaneously small space usage and fast retrieval.