A Unified Energy-based Framework for Learning to Rank

Learning to Rank (L2R) has emerged as one of the core machine learning techniques for IR. On the other hand, Energy-Based Models (EBMs) capture dependencies between variables by associating a scalar energy to each configuration of the variables. They have produced impressive results in many computer vision and speech recognition tasks. In this paper, we introduce a unified view of Learning to Rank that integrates various L2R approaches in an energy-based ranking framework. In this framework, an energy function associates low energies to desired documents and high energies to undesired results. Learning is essentially the process of shaping the energy surface so that desired documents have lower energies. The proposed framework yields new insights into learning to rank. First, we show how various existing L2R models (pointwise, pairwise, and listwise) can be cast in the energy-based framework. Second, new L2R models can be constructed based on existing EBMs. Furthermore, inspired by the intuitive learning process of EBMs, we can devise novel energy-based models for ranking tasks. We introduce several new energy-based ranking models based on the proposed framework. The experiments are conducted on the public LETOR 4.0 benchmarks and demonstrate the effectiveness of the proposed models.