Probabilistic Word Embeddings in Neural IR: A Promising Model That Does Not Work as Expected (For Now)

In this paper, we discuss how a promising word vector representation based on Probabilistic Word Embeddings (PWE) can be applied to Neural Information Retrieval (NeuIR). We illustrate PWE pros for text retrieval, and identify the core issues which prevent a full exploitation of their potential. In particular, we focus on the application of elliptical probabilistic embeddings, a type of PWE, to a NeuIR system (i.e., MatchPyramid). The main contributions of this paper are: (i) an analysis of the pros and cons of PWE in NeuIR; (ii) an in-depth comparison of PWE against pre-trained Word2Vec, FastText and WordNet word embeddings; (iii) an extension of the MatchPyramid model to take advantage of broader word relations information from WordNet; (iv) a topic-level evaluation of the MatchPyramid ranking models employing the considered word embeddings. Finally, we discuss some lessons learned and outline some open research problems to employ PWE in NeuIR systems more effectively.