Listwise Generative Retrieval Models via a Sequential Learning Process

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Abstract
Recently, a novel generative retrieval (GR) paradigm has been proposed, where a single sequence-to-sequence model is learned to directly generate a list of relevant document identifiers (docids) given a query. Existing GR models commonly employ maximum likelihood estimation (MLE) for optimization: This involves maximizing the likelihood of a single relevant docid given an input query, with the assumption that the likelihood for each docid is independent of the other docids in the list. We refer to these models as the pointwise approach in this article. While the pointwise approach has been shown to be effective in the context of GR, it is considered sub-optimal due to its disregard for the fundamental principle that ranking involves making predictions about lists. In this article, we address this limitation by introducing an alternative listwise approach, which empowers the GR model to optimize the relevance at the docid list level. Specifically, we view the generation of a ranked docid list as a sequence learning process: At each step, we learn a subset of parameters that maximizes the corresponding generation likelihood of theith docid given the (preceding) topi-1 docids. To formalize the sequence learning process, we design a positional conditional probability for GR. To alleviate the potential impact of beam search on the generation quality during inference, we perform relevance calibration on the generation likelihood of model-generated docids according to relevance grades. We conduct extensive experiments on representative binary and multi-graded relevance datasets. Our empirical results demonstrate that our method outperforms state-of-the-art GR baselines in terms of retrieval performance.
Funding Information
  • Strategic Priority Research Program of the CAS (XDB0680102)
  • National Key Research and Development Program of China (2023YFA1011602, JCKY2022130C039)
  • Lenovo-CAS Joint Lab Youth Scientist Project
  • CAS Project for Young Scientists in Basic Research (YSBR-034)
  • Innovation Project of ICT CAS (E261090)
  • Hybrid Intelligence Center
  • Dutch Ministry of Education, Culture and Science
  • Netherlands Organisation for Scientific Research
  • LESSEN (NWA.1389.20.183)
  • Dutch Research Council
  • FINDHR
  • European Union’s Horizon Europe (101070212)