Fast Passage Re-ranking with Contextualized Exact Term Matching and Efficient Passage Expansion
Fast Passage Re-ranking with Contextualized Exact Term Matching and Efficient Passage Expansion
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通过上下文精确术语匹配和高效的段落扩展进行快速的段落重新排序
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发表时间：
2021
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通讯作者：
G. Zuccon
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作者：
Shengyao Zhuang;G. Zuccon
基于bert的信息检索模型在时间（查询延迟）和计算资源（能源、硬件成本）上都是昂贵的，这使得许多模型在资源限制下尤其不切实际。依赖于只执行标记化的查询编码器和索引时通道表示的预处理，使得最近提出的TILDE方法克服了基于bert的模型典型的高查询延迟问题。然而，与其他基于bert的重新排序器和密集寻回器相比，这是以较低的效率为代价的。此外，原始的TILDE方法的特点是索引占用非常高的内存，因为它将每个段落扩展到BERT词汇表的大小。在本文中，我们提出了TILDEv2，这是一种源于原始TILDE的新模型，但解决了其局限性。TILDEv2依赖于上下文化的精确术语匹配与扩展的段落。这需要在索引中只存储扩展段落中出现的标记的分数（而不是所有词汇表），因此生成的索引比TILDE的索引小99%。这种匹配机制还可以在不增加查询延迟的情况下将排名效率提高24%。这使得TILDEv2成为仅cpu环境的最先进的通道重新排序方法，能够在普通硬件上保持低于100ms的查询延迟。
BERT-based information retrieval models are expensive, in both time (query latency) and computational resources (energy, hardware cost), making many of these models impractical especially under resource constraints. The reliance on a query encoder that only performs tokenization and on the pre-processing of passage representations at indexing, has allowed the recently proposed TILDE method to overcome the high query latency issue typical of BERT-based models. This however is at the expense of a lower effectiveness compared to other BERT-based re-rankers and dense retrievers. In addition, the original TILDE method is characterised by indexes with a very high memory footprint, as it expands each passage into the size of the BERT vocabulary. In this paper, we propose TILDEv2, a new model that stems from the original TILDE but that addresses its limitations. TILDEv2 relies on contextualized exact term matching with expanded passages. This requires to only store in the index the score of tokens that appear in the expanded passages (rather than all the vocabulary), thus producing indexes that are 99% smaller than those of TILDE. This matching mechanism also improves ranking effectiveness by 24%, without adding to the query latency. This makes TILDEv2 the state-of-the-art passage re-ranking method for CPU-only environments, capable of maintaining query latency below 100ms on commodity hardware.