A knowledge graph (KG) contains rich information about users and items. The relationship among users and items can help to generate intuitive explanations for recommended items. Many variations of KG-based recommendation algorithms use the shortest path from the user to the item in order to generate an explanation of the recommendation. However, the simple shortest path may not be useful in the case when the path is long, because the interpretation of the long path is difficult. Also, there may be no path between the user and the recommended item. In order to overcome these difficulties, we proposed an extension of the existing framework based on random walk with KG embedding. In the proposed framework, we use the most probable path in a random walk as an explanation. Thereby, our framework can even explain items that have no connection in the KG due to the latent connection resulting from random walk teleportation. Comparison experiment demonstrated that the framework can provide more suitable recommendations than the existing method. In addition, the experiment show the ability of the proposed method to generate explanation for all recommendations that have no path in the graph.

A number of knowledge graph (KG)-based recommendation algorithms have been introduced; KGs enable users and items and their attributes to be treated in an integrated way and structural information to be captured through graphs. There are many variations of the KG based recommendation algorithms. Among them, KG embedding is often used, but doing this does not take advantage of the meta-path-level proximity between users and items. This paper presents a flexible framework combining random walk and KG embedding methods. The random walk model is formulated on the basis of the similarity between nodes revealed by the KG embedding. This enables the metapath level proximity of users and items to be efficiently utilized. Comparison testing demonstrated that the proposed framework performs better than random- walk-only methods and KG-embedding-only methods, and slightly better than the existing method we have extended.

Molecular graphs are one of the established representations for small molecules, and even steric or electronic information can be encoded as node and edge features. Naturally, graph neural networks have been intensively investigated to solve various chemical problems at molecular levels. However, it remains unclear how to encode relevant chemical information into graphs. We investigate this problem by proposing three models of graph neural networks with self-attention mechanisms at different levels to adaptively select relevant chemical information for each input. Using neural graph fingerprint (NFP) as a baseline, we introduce three types of attention mechanisms on the top of NFPs. Our experimental evaluations suggest that introducing these self-attention mechanisms contributes to not only improving the prediction accuracy but also providing quantitative interpretation using obtained attention coefficients.

Recommender systems using a knowledge graph can comprehensively organize users and items and their attributes and thereby improve recommendation performance. In addition, the relationship between users and items can be easily interpreted on the basis of entities and relations, thus giving explanations to recommendations. The algorithms and knowledge graphs used for generating explanations have not utilized review text. We have developed a recommendation method for predicting interactions between users and items using a knowledge graph and review text. The underlying user-item relationships are reflected and explanations are generated by predicting user-item interactions from the paths between a user and an item. The modeling is done using a recurrent neural network or a factorization machine. Items' aspects that interest users are extracted from review text and leveraged using an attention-like mechanism. Since the path between a user and an item can be easily interpreted, and the important aspects between a user and an item can be interpreted by observing the attention weight, the proposed model can generate a reasonable recommendation explanation. Testing using a real-world dataset demonstrated that the proposed model can explain the recommendations.

Explaining recommendations helps users to make more accurate and effective decisions and improves system credibility and transparency. Current explainable recommender systems tend to provide fixed statements such as "customers who purchased this item also purchased....". This explanation is generated only on the basis of the purchase history of similar customers, so it does not include the preferences of customers who have purchased the item or a description of the item. Since user-generated reviews generally contain information about the reviewer's preferences and a description of the item, such reviews typically have more effect on purchase decisions. Therefore, using reviews to explain recommendations should be more useful than providing only a fixed statement explanation. Aiming to create a system that provides personalized explanations for recommendations, we have developed a recurrent neural network model that uses multicriteria evaluation data to generate reviews.

Ratings by users on various items such as hotels and movies have become easily available on the Web. In many cases, other than overall rating for each item by each user, more detailed information such as ratings from different viewpoints and free text comments, as well as aggregated information such as the average of ratings by different users, are also available. We investigated the effectiveness of six existing collaborative filtering methods for large-scale sparse multicriteria rating data. We formulated rating aggregation as a collaborative filtering problem and applied six collaborative filtering methods to it. Furthermore, we extended three of the methods to calculate user similarity using indirect users and review comments and applied them to collaborative filtering and rating aggregation. The results show that multicriteria rating approaches perform better than single criterion rating approaches. The extended methods had better performance both in collaborative filtering and in rating aggregation.

Despite recent open data initiatives in many countries, a significant percentage of the data provided is in non-machine-readable formats like image format rather than in a machine-readable electronic format, thereby restricting their usability. This paper describes the first unified framework for converting legacy open data in image format into a machine-readable and reusable format by using crowdsourcing. Crowd workers are asked not only to extract data from an image of a chart but also to reproduce the chart objects in spreadsheets. The properties of the reconstructed chart objects give their data structures including series names and values, which are useful for automatic processing of data by computer. Since results produced by crowdsourcing inherently contain errors, a quality control mechanism was developed that improves the accuracy of extracted tables by aggregating tables created by different workers for the same chart image and by utilizing the data structures obtained from the reproduced chart objects. Experimental results demonstrated that the proposed framework and mechanism are effective.

We develop a flexible reward plan to elicit truthful predictive probability distribution over a set of uncertain events from workers. In our reward plan, the principal can assign rewards for incorrect predictions according to her similarity between events. In the spherical proper scoring rule, a worker's expected utility is represented as the inner product of her truthful predictive probability and her declared probability. We generalize the inner product by introducing a reward matrix that defines a reward for each prediction-outcome pair. We show that if the reward matrix is symmetric and positive definite, the spherical proper scoring rule guarantees the maximization of a worker's expected utility when she truthfully declares her prediction.

The increasing interest in dynamically changing networks has led to growing interest in a more general link prediction problem called temporal link prediction in the data mining and machine learning communities. However, only links in identical time frames are considered in temporal link prediction. We propose a new link prediction problem called cross-temporal link prediction in which the links among nodes in different time frames are inferred. A typical example of cross-temporal link prediction is cross-temporal entity resolution to determine the identity of real entities represented by data objects observed in different time periods. In dynamic environments, the features of data change over time, making it difficult to identify cross-temporal links by directly comparing observed data. Other examples of cross-temporal links are asynchronous communications in social networks such as Face book and Twitter, where a message is posted in reply to a previous message. We adopt a dimension reduction approach to cross-temporal link prediction, that is, data objects in different time frames are mapped into a common low-dimensional latent feature space, and the links are identified on the basis of the distance between the data objects. The proposed method uses different low-dimensional feature projections in different time frames, enabling it to adapt to changes in the latent features over time. Using multi-task learning, it jointly learns a set of feature projection matrices from the training data, given the assumption of temporal smoothness of the projections. The optimal solutions are obtained by solving a single generalized eigenvalue problem. Experiments using a real-world set of bibliographic data for cross-temporal entity resolution showed that introducing time-dependent feature projections improves the accuracy of link prediction.

We propose a query-by-example geographic object search method for users that do not know well about the place they are in. Geographic objects, such as restaurants, are often retrieved using an attribute-based or keyword query. These queries, however, are difficult to use for users that have little knowledge on the place where they want to search. The proposed query-by-example method allows users to query by selecting examples in familiar places for retrieving objects in unfamiliar places. One of the challenges is to predict an effective distance metric, which varies for individuals. Another challenge is to calculate the distance between objects in heterogeneous domains considering the feature gap between them, for example, restaurants in Japan and China. Our proposed method is used to robustly estimate the distance metric by amplifying the difference between selected and non-selected examples. By using the distance metric, each object in a familiar domain is evenly assigned to one in an unfamiliar domain to eliminate the difference between those domains. We developed a restaurant search using data obtained from a Japanese restaurant Web guide to evaluate our method.

We describe methods to search with a query by example in a known domain for information in an unknown domain by exploiting Web search engines. Relational search is an effective way to obtain information in an unknown field for users. For example, if an Apple user searches for Microsoft products, similar Apple products are important clues for the search. Even if the user does not know keywords to search for specific Microsoft products, the relational search returns a product name by querying simply an example of Apple products. More specifically, given a tuple containing three terms, such as (Apple, iPod, Microsoft), the term Zune can be extracted from the Web search results, where Apple is to iPod what Microsoft is to Zune. As a previously proposed relational search requires a huge text corpus to be downloaded from the Web, the results are not up-to-date and the corpus has a high construction cost. We introduce methods for relational search by using Web search indices. We consider methods based on term co-occurrence, on lexico-syntactic patterns, and on combinations of the two approaches. Our experimental results showed that the combination methods got the highest precision, and clarified the characteristics of the methods.

A method is described for discovering coordinate terms, such as "Honda'' and "Nissan,'' for a given term, such as "Toyota,'' as well as their common topic terms, from the query logs of a Web search engine. Coordinate terms are good candidates for use in making comparisons. A HITS-based algorithm is applied to a bipartite graph between coordinate term candidates and co-occurrence patterns to identify coordinate and topic terms. Spectral analysis is used to distinguish coordinate terms corresponding to different aspects of the search term. As a result, we can discover terms related to the terms in a search engine query that reflect the needs and interests of the user.

Domain-specific Web search engines are effective tools for reducing the difficulty experienced when acquiring information from the Web. Existing methods for building domain-specific Web search engines require human expertise or specific facilities. However, we can build a domain-specific search engine simply by adding domain-specific keywords, called "keyword spices," to the user's input query and forwarding it to a general-purpose Web search engine. Keyword spices can be effectively discovered from Web documents using machine learning technologies. The paper describes domain-specific Web search engines that use keyword spices for locating recipes, restaurants, and used cars.

Conventional Web bookmarks only contain URLs and titles of Web pages that users are interested in. This makes the process of remembering, sharing or ranking such pages difficult. The "context" of users' navigation can be described as collections of browsed pages. Conventional bookmarks do not contain such information. We believe that such context information conveys the users' intention and the importance of bookmarks. We introduce a notion of context-dependent Web bookmarks that reflects users' browsing histories. A context-dependent Web bookmark consists of (1) representative keywords of bookmarked pages and browsed pages, (2) the ranking value of bookmarked pages calculated by its context, as well as the URL and title of the page that the user bookmarked. Context-dependent bookmarks will make it possible for users to remember the situation of the bookmarking process, grasp the degree of significance of the bookmark, and share the bookmark among multiple users. Furthermore, it becomes possible to re-use context-dependent bookmarks as queries, which could be executed for unvisited Web pages. We also describe our Web browser prototype system based on the context-dependent bookmark function, and our experimental results.

A digital city is a social information infrastructure for urban life (including shopping, business, transportation, education, welfare and so on). We started a project to develop a digital city for Kyoto based on the newest technologies including cooperative information agents. This paper presents an architecture for digital cities and shows the roles of agent interfaces in it. We propose two types of cooperative information agents as follows: (a) the front-end agents determine and refine users' uncertain goals, (b) the back-end agents extract and organize relevant information from the Internet, (c) Both types of agents opportunistically cooperate through a blackboard. We also show the research guidelines towards social agents in digital cities; the agent will foster social interaction among people who are living in/visiting the city.