Systematically discovering semantic relationships in text is an important and extensively studied area in Natural Language Processing, with various tasks such as entailment, semantic similarity, etc. Decomposability of sentence-level scores via subsequence alignments has been proposed as a way to make models more interpretable. We study the problem of aligning components of sentences leading to an interpretable model for semantic textual similarity. In this paper, we introduce a novel pointer network based model with a sentinel gating function to align constituent chunks, which are represented using BERT. We improve this base model with a loss function to equally penalize misalignments in both sentences, ensuring the alignments are bidirectional. Finally, to guide the network with structured external knowledge, we introduce first-order logic constraints based on ConceptNet and syntactic knowledge. The model achieves an F1 score of 97.73 and 96.32 on the benchmark SemEval datasets for the chunk alignment task, showing large improvements over the existing solutions. Source code is available at https://github.com/manishb89/interpretable_sentence_similarity

E-commerce customers express their purchase intents in several ways, some of which may use a different vocabulary than that of the product catalog. For example, the intent for "women maternity gown" is often expressed with the query, "ladies pregnancy dress". Search engines typically suffer from poor performance on such queries because of low overlap between query terms and specifications of the desired products. Past work has referred to these queries as vocabulary gap queries. In our experiments, we show that our technique significantly outperforms strong baselines and also show its real-world effectiveness with an online A/B experiment.