Novel inverted index-based learned sparse ranking models provide more effective, but less efficient, retrieval performance compared to traditional ranking models like BM25. In this paper, we introduce a technique we call postings clipping to improve the query efficiency of learned representations. Our technique amplifies the benefit of dynamic pruning query processing techniques by accounting for changes in term importance distributions of learned ranking models. The new clipping mechanism accelerates top-k retrieval by up to 9.6X without any loss in effectiveness.

Efficient methods for storing and querying are critical for scaling high-order m-gram language models to large corpora. We propose a language model based on compressed suffix trees, a representation that is highly compact and can be easily held in memory, while supporting queries needed in computing language model probabilities on-the-fly. We present several optimisations which improve query runtimes up to 2500×, despite only incurring a modest increase in construction time and memory usage. For large corpora and high Markov orders, our method is highly competitive with the state-of-the-art KenLM package. It imposes much lower memory requirements, often by orders of magnitude, and has runtimes that are either similar (for training) or comparable (for querying).

Succinct data structures involve the use of novel data structures, compression technologies, and other mechanisms to allow data to be stored in extremely small memory or disk footprints, while still allowing for efficient access to the underlying data. They have successfully been applied in areas such as Information Retrieval and Bioinformatics to create highly compressible in-memory search indexes which provide efficient search functionality over datasets which traditionally could only be processed using external memory data structures. Modern technologies in this space are not well known within the NLP community, but have the potential to revolutionise NLP, particularly the application to ‘big data’ in the form of terabyte and larger corpora. This tutorial will present a practical introduction to the most important succinct data structures, tools, and applications with the intent of providing the researchers with a jump-start into this domain. The focus of this tutorial will be efficient text processing utilising space efficient representations of suffix arrays, suffix trees and searchable integer compression schemes with specific applications of succinct data structures to common NLP tasks such as n-gram language modelling.