Abstract: We study the problem of semantic matching in product search, that is, given a customer query, retrieve all semantically related products from the catalog. Pure lexical matching via an inverted index falls short in this respect due to several factors: a) lack of understanding of hypernyms, synonyms, and antonyms, b) fragility to morphological variants (e.g."woman"vs."women"), and c) sensitivity to spelling errors. To address these issues, we train a deep learning model for semantic matching using customer behavior data. Much of the recent work on large-scale semantic search using deep learning focuses on ranking for web search. In contrast, semantic matching for product search presents several novel challenges, which we elucidate in this paper. We address these challenges by a) developing a new loss function that has an inbuilt threshold to differentiate between random negative examples, impressed but not purchased examples, and positive examples (purchased items), b) using average pooling in conjunction with n-grams to capture short-range linguistic patterns, c) using hashing to handle out of vocabulary tokens, and d) using a model parallel training architecture to scale across 8 GPUs. We present compelling offline results that demonstrate at least 4.7% improvement in Recall@100 and 14.5% improvement in mean average precision (MAP) over baseline state-of-the-art semantic search methods using the same tokenization method. Moreover, we present results and discuss learnings from online A/B tests which demonstrate the efficacy of our method.

Introduction: At a high level, as shown in Figure FIGREF4 , a product search engine works as follows: a customer issues a query, which is passed to a lexical matching engine (typically an inverted index BIBREF0 , BIBREF1 ) to retrieve all products that contain words in the query, producing a match set. The match set passes through stages of ranking, wherein top results from the previous stage are re-ranked before the most relevant items are finally displayed. It is imperative that the match set contain a relevant and diverse set of products that match the customer intent in order for the subsequent rankers to succeed. However, inverted index-based lexical matching falls short in several key aspects: In this paper, we address the question: Given rich customer behavior data, can we train a deep learning model to retrieve matching products in response to a query? Intuitively, there is reason to believe that customer behavior logs contain semantic information; customers who are intent on purchasing a product circumvent the limitations of lexical matching by query reformulation or by deeper exploration of the search results. The challenge is the sheer magnitude of the data as well as the presence of noise, a challenge that modern deep learning techniques address very effectively. Product search is different from web search as the queries tend to be shorter and the positive signals (purchases) are sparser than clicks. Models based on conversion rates or click-through-rates may incorrectly favor accessories (like a phone cover) over the main product (like a cell phone). This is further complicated by shoppers maintaining multiple intents during a single search session: a customer may be looking for a specific television model while also looking for accessories for this item at the lowest price and browsing additional products to qualify for free shipping. A product search engine should reduce the effort needed from a customer with a specific mission (narrow queries) while allowing shoppers to explore when they are looking for inspiration (broad queries). As mentioned, product search typically operates in two stages: matching and ranking. Products that contain words in the query ( INLINEFORM0 ) are the primary candidates. Products that have prior behavioral associations (products bought or clicked after issuing a query INLINEFORM1 ) are also included in the candidate set. The ranking step takes these candidates and orders them using a machine-learned rank function to optimize for customer satisfaction and business metrics. We present a neural network trained with large amounts of purchase and click signals to complement a lexical search engine in ad hoc product retrieval. Our first contribution is a loss function with a built-in threshold to differentiate between random negative, impressed but not purchased, and purchased items. Our second contribution is the empirical result that recommends average pooling in combination with INLINEFORM0 -grams that capture short-range linguistic patterns instead of more complex architectures. Third, we show the effectiveness of consistent token hashing in Siamese networks for zero-shot learning and handling out of vocabulary tokens. In Section SECREF2 , we highlight related work. In Section SECREF3 , we describe our model architecture, loss functions, and tokenization techniques including our approach for unseen words. We then introduce the readers to the data and our input representations for queries and products in Section SECREF4 . Section SECREF5 presents the evaluation metrics and our results. We provide implementation details and optimizations to efficiently train the model with large amounts of data in Section SECREF6 . Finally, we conclude in Section SECREF7 with a discussion of future work.

Question: What dataset is used for training?
Answer: a self-collected dataset of 11 months of search logs as query-product pairs