KGPR: Knowledge Graph Enhanced Passage Ranking

Passage ranking aims to rank a set of passages based on their relevance to a query. Current state-of-the-art models for this task typically employ a cross-encoder structure. However, these models lack access to background knowledge, i.e., information related to the query that can be helpful in retrieving relevant passages. Knowledge Graphs (KGs) provide a structured way of storing information about entities and their relationships, offering valuable background knowledge about entities. While KGs have been used to augment pretrained language models (LMs) to perform several reasoning tasks such as question answering, it remains an open question of how to utilise the information from KGs to enhance the performance of cross-encoders on the passage ranking task. Therefore, we propose KGPR, a KG-enhanced cross-encoder for the Passage Retrieval task. KGPR is built upon LUKE, an entity-aware pretrained LM, with an additional module that fuses information from KGs into LUKE. By leveraging the background knowledge from KGs, KGPR enhances the model's comprehension of queries and passages, resulting in improved ranking performance. Experimental results demonstrate that using KGs can enhance the performance of LUKE in the passage retrieval task, and KGPR can outperform state-of-the-art monoT5 cross-encoder by 3.32% and 10.77% on the MS MARCO development set and TREC DL-HARD query set respectively, using a model with a similar number of parameters.