Chandra Sekhar Bhagavatula completed his PhD from Northwestern University in 2016, under the supervision of Prof. Doug Downey. His research interests are in the areas of Information Extraction, Natural Language Processing and he is currently exploring the application of Machine Learning algorithms to build Semantic Scholar, AI2’s academic search engine. Besides research, he likes to travel, enjoys water sports and would like to learn to play the flute someday.
- Chandra Bhagavatula, Thanapon Noraset, Doug DowneyISWC 2015
Web tables form a valuable source of relational data. The Web contains an estimated 154 million HTML tables of relational data, with Wikipedia alone containing 1.6 million high-quality tables. Extracting the semantics of Web tables to produce machine-understandable knowledge has become an active area of research. A key step in extracting the semantics of Web content is entity linking (EL): the task of mapping a phrase in text to its referent entity in a knowledge base (KB). In this paper we present TabEL, a new EL system for Web tables. TabEL differs from previous work by weakening the assumption that the semantics of a table can be mapped to pre-defined types and relations found in the target KB. Instead, TabEL enforces soft constraints in the form of a graphical model that assigns higher likelihood to sets of entities that tend to co-occur in Wikipedia documents and tables. In experiments, TabEL significantly reduces error when compared to current state-of-the-art table EL systems, including a 75% error reduction on Wikipedia tables and a 60% error reduction on Web tables. We also make our parsed Wikipedia table corpus and test datasets publicly available for future work.
- Doug Downey, Chandra Bhagavatula, Yi YangACL2015
Latent variable topic models such as Latent Dirichlet Allocation (LDA) can discover topics from text in an unsupervised fashion. However, scaling the models up to the many distinct topics exhibited in modern corpora is challenging. " Flat " topic models like LDA have difficulty modeling sparsely expressed topics, and richer hierarchical models become compu-tationally intractable as the number of topics increases. In this paper, we introduce efficient methods for inferring large topic hierarchies. Our approach is built upon the Sparse Backoff Tree (SBT), a new prior for latent topic distributions that organizes the latent topics as leaves in a tree. We show how a document model based on SBTs can effectively infer accurate topic spaces of over a million topics. We introduce a collapsed sampler for the model that exploits sparsity and the tree structure in order to make inference efficient. In experiments with multiple data sets, we show that scaling to large topic spaces results in much more accurate models, and that SBT document models make use of large topic spaces more effectively than flat LDA.
- Thanapon Noraset, Chandra Bhagavatula, Doug DowneyEMNLP2014
Wikipedia's link structure is a valuable resource for natural language processing tasks, but only a fraction of the concepts mentioned in each article are annotated with hyperlinks. In this paper, we study how to augment Wikipedia with additional high-precision links. We present 3W, a system that identifies concept mentions in Wikipedia text, and links each mention to its referent page. 3W leverages rich semantic information present in Wikipedia to achieve high precision. Our experiments demonstrate that 3W can add an average of seven new links to each Wikipedia article, at a precision of 0.98.
- Chandra Bhagavatula, Thanapon Noraset, Doug DowneyKDD (IDEA workshop)2013
Knowledge bases extracted automatically from the Web present new opportunities for data mining and exploration. Given a large, heterogeneous set of extracted relations, new tools are needed for searching the knowledge and uncovering relationships of interest. We present WikiTables, a Web application that enables users to interactively explore tabular knowledge extracted from Wikipedia. In experiments, we show that WikiTables substantially outperforms baselines on the novel task of automatically joining together disparate tables to uncover "interesting" relationships between table columns. We find that a "Semantic Relatedness" measure that leverages the Wikipedia link structure accounts for a majority of this improvement. Further, on the task of keyword search for tables, we show that WikiTables performs comparably to Google Fusion Tables despite using an order of magnitude fewer tables. Our work also includes the release of a number of public resources, including over 15 million tuples of extracted tabular data, manually annotated evaluation sets, and public APIs.