Query suggestion (QS) in web search must provide efficient and up-to-date suggestions that are relevant to the session context. Recent studies treat QS as generation, which captures session context well but suffers from high latency and costly retraining to maintain information freshness. In this study, we recast QS as dense retrieval: given a search session, the next query is retrieved from a large index of historical queries using efficient approximate nearest neighbor search. We propose Context-aware Asymmetric Dual Encoder for QS (CADE-QS), which uses an asymmetric dual encoder to model query -to- suggestion dependency and incorporates session history into the query encoder via context-aware contrastive learning. We evaluate our method on two real-world search-log datasets: a recent Japanese web search log and the public AOL log. CADE-QS rivals strong generative baselines in quality while reducing end-to-end latency to around 30 ms on CPU, representing an order-of-magnitude improvement. Detailed analyses confirm CADE-QS's robust context awareness, unidirectional modeling, and practicality for reflecting evolving information via index refreshes, as well as the effectiveness of an adaptive hybrid strategy for low-coverage scenarios. Our code is publicly available at https://github.com/lycorp-jp/cadeqs.

To prevent and curb viral outbreaks, such as COVID-19, it is important to increase vaccination coverage while resolving vaccine hesitancy and refusal. To understand why COVID-19 vaccination coverage had rapidly increased in Japan, we analyzed Twitter posts (tweets) to track the evolution of people's stance on vaccination and clarify the factors of why people decide to vaccinate. We collected all Japanese tweets related to vaccines over a five-month period and classified the vaccination stances of users who posted those tweets by using a deep neural network we designed. Examining diachronic changes in the users' stances on this large-scale vaccine dataset, we found that a certain number of neutral users changed to a pro-vaccine stance while very few changed to an anti-vaccine stance in Japan. Investigation of their information-sharing behaviors revealed what types of users and external sites were referred to when they changed their stances. These findings will help increase coverage of booster doses and future vaccinations.

Twitter is currently one of the most influential microblogging services on which users interact with messages. It is imperative to grasp the big picture of Twitter through analyzing its huge stream data. In this study, we develop a two-stage clustering method that automatically discovers coarse-grained topics from Twitter data. In the first stage, we use graph clustering to extract micro-clusters from the word co-occurrence graph. All the tweets in a micro-cluster share a fine-grained topic. We then obtain the time series of each micro-cluster by counting the number of tweets posted in a time window. In the second stage, we use time series clustering to identify the clusters corresponding to coarse-grained topics. We evaluate the computational efficacy of the proposed method and demonstrate its systematic improvement in scalability as the data volume increases. Next, we apply the proposed method to large-scale Twitter data (26 million tweets) about the COVID-19 Vaccination in Japan. The proposed method separately identifies the reactions to news and the reactions to tweets.

This paper presents a method for finding a specification page on the web for a given object (e.g."Titanic ö)and its class label (e.g."film ö). A specification page for an object is a web page which gives concise attribute-value information about the object (e.g."director ö-"James Cameron öfor "Titanic ö). A simple unsupervised method using layout and symbolic decoration cues was applied to a large number of web pages to acquire the class attributes. We used these acquired attributes to select a representative specification page for a given object from the web pages retrieved by a normal search engine. Experimental results revealed that our method greatly outperformed the normal search engine in terms of specification retrieval.