Emmanouil Georgios Lionis

dblp:402/5737 · DBLP profile ↗
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5ranked-venue papers in the field
3as first author
5since 2021 · last 2026
0009-0004-3931-9657ORCID · corroborated

Domains — venue-derived; a paper can count in several

Information Retrieval & Web Search · 5 (3 first)
YearPublicationVenuePosition
2026 To Case or Not to Case: An Empirical Study in Learned Sparse Retrieval
Emmanouil Georgios Lionis, Jia-Huei Ju, Angelos Nalmpantis, Casper Thuis, Sean MacAvaney, Andrew Yates
ECIR (1)1
2026 Pipeline Inspection, Visualization, and Interoperability in PyTerrier
Emmanouil Georgios Lionis, Craig Macdonald, Sean MacAvaney
ECIR (4)1
2026 Towards a Relevance Posterior in Neural Information Access
abstract
Modern information retrieval systems typically operationalise relevance as a query-conditional score computed at inference time. This design choice has become dominant such that alternative decompositions of relevance are rarely discussed, despite the long history of document and query priors in probabilistic retrieval and large-scale search. As neural ranking models grow more computationally expensive and retrieval pipelines expand to include multi-stage ranking, recommendation, and retrieval-augmented generation, this monolithic view of query-time scoring becomes increasingly limiting. We argue that modern information access systems are more naturally understood as performing approximate posterior inference, in which relevance is refined through a staged combination of query-dependent likelihoods and query-independent priors. We extend classical probabilistic retrieval formalisms to contemporary learned systems and show how explicit likelihood-prior decomposition exposes new opportunities to shift computation offline while disentangling document-level and interaction-level beliefs. We present empirical evidence that incorporating query-independent document utility can complement existing rankers and improve effectiveness with minimal query-time computation (solely score fusion). Concretely, a learned prior improves first-stage retrieval through rank fusion (up to Δ nDCG@10 ≈ 0.046 on TREC DL-2019 and ≈ 0.029 on TREC DL-2020) and also improves downstream re-ranking, with the largest gains observed for the LLM re-ranker RankZephyr (up to Δ nDCG@10 ≈ 0.054 on TREC DL-2020). Finally, we discuss how this decomposition connects to broader information access and outline research directions for designing retrieval systems that explicitly allocate modelling capacity between offline priors and online interaction.
Andrew Parry, Emmanouil Georgios Lionis, Debasis Ganguly, Sean MacAvaney
SIGIR2
2025 On the Reproducibility of Learned Sparse Retrieval Adaptations for Long Documents
Emmanouil Georgios Lionis, Jia-Huei Ju
ECIR (4)1
2025 Information Leakage of Sentence Embeddings via Generative Embedding Inversion Attacks
abstract
Text data are often encoded as dense vectors, known as embeddings, which capture semantic, syntactic, contextual, and domain-specific information. These embeddings, widely adopted in various applications, inherently contain rich information that may be susceptible to leakage under certain attacks. The GEIA framework highlights vulnerabilities in sentence embeddings, demonstrating that they can reveal the original sentences they represent. In this study, we reproduce GEIA's findings across various neural sentence embedding models. Additionally, we contribute new analysis to examine whether these models leak sensitive information from their training datasets. We propose a simple yet effective method without any modification to the attacker's architecture proposed in GEIA. The key idea is to examine differences between log-likelihood for masked and original variants of data that sentence embedding models have been pre-trained on, calculated on the embedding space of the attacker. Our findings indicate that following our approach, an adversary party can recover meaningful sensitive information related to the pre-training knowledge of the popular models used for creating sentence embeddings, seriously undermining their security. Our code is available on: https://github.com/taslanidis/GEIA
Antonios Tragoudaras, Theofanis Aslanidis, Emmanouil Georgios Lionis, Marina Orozco González, Panagiotis Eustratiadis
SIGIR3