Semantic Triple Encoder for Fast Open-Set Link Prediction

We improve both the open-set generalization and efficiency of link prediction on knowledge graphs by leveraging the contexts of entities and relations in a novel semantic triple encoder. Most previous methods, e.g., translation-based and GCN-based embedding approaches, were built upon graph embedding models. They simply treat the entities/relations as a closed set of graph nodes regardless of their context semantics, which however cannot provide critical information for the generalization to unseen entities/relations. In this paper, we partition each graph triple and develop a novel context-based encoder that separately maps each part and its context into a latent semantic space. We train this semantic triple encoder by optimizing two objectives specifically designed for link prediction. In particular, (1) We split each triple into two parts, i.e., i) head entity plus relation and ii) tail entity, process both contexts separately by a Transformer encoder, and combine the encoding outputs to derive the prediction. This Siamese-like architecture avoids the combinatorial explosion of candidate triples and significantly improves the efficiency, especially during inference; (2) We cover the contextualized semantics of the triples in the encoder so it can handle unseen entities during inference, which promisingly improves the generalization ability; (3) We train the model by optimizing two complementary objectives defined on the triple, i.e., classification and contrastive losses, for natural and reliable ranking scores during inference. In experiments, we achieve the state-of-the-art or competitive performance on three popular link prediction benchmarks. In addition, we empirically reduce the inference costs by one or two orders of magnitude compared to a recent context-based encoding approach and meanwhile keep a superior quality of prediction.