Prof. Dr. Felix Naumann


Two papers accepted at JCDL 2018

Stefan Bunk, Ralf Krestel, Julian Risch

The results of the Master's theses by Stefan Bunk and Julian Risch have been accepted for presentation at the Joint Conference on Digital Libraries (JCDL), which takes place from June 3rd to 6th, 2018, in Fort Worth, Texas. The two papers are titled "WELDA: Enhancing Topic Models by Incorporating Local Word Context" (Stefan Bunk, Ralf Krestel) and "My Approach = Your Apparatus? Entropy-Based Topic Modeling on Multiple Domain-Specific Text Collections" (Julian Risch, Ralf Krestel).

WELDA: Enhancing Topic Models by Incorporating Local Word Context

The distributional hypothesis states that similar words tend to have similar contexts in which they occur. Word embedding models exploit this hypothesis by learning word vectors based on the local context of words. Probabilistic topic models on the other hand utilize word co-occurrences across documents to identify topically related words. Due to their complementary nature, these models define different notions of word similarity, which, when combined, can produce better topical representations. In this paper we propose WELDA, a new type of topic model, which combines word embeddings (WE) with latent Dirichlet allocation (LDA) to improve topic quality. We achieve this by estimating topic distributions in the word embedding space and exchanging selected topic words via Gibbs sampling from this space. We present an extensive evaluation showing that WELDA cuts runtime by at least 30% while outperforming other combined approaches with respect to topic coherence and for solving word intrusion tasks.

My Approach = Your Apparatus?
Entropy-Based Topic Modeling on Multiple Domain-Specific Text Collections

Comparative text mining extends from genre analysis and political bias detection to the revelation of cultural and geographic differences, through to the search for prior art across patents and scientific papers. ŒThese applications use cross-collection topic modeling for the exploration, clustering, and comparison of large sets of documents, such as digital libraries. However, topic modeling on documents from different collections is challenging because of domain-specific vocabulary. We present a cross-collection topic model combined with automatic domain term extraction and phrase segmentation. ŒThis model distinguishes collection-€specific and collection-independent words based on information entropy and reveals commonalities and differences of multiple text collections. We evaluate our model on patents, scientific papers, newspaper articles, forum posts, and Wikipedia articles. In comparison to state-of-the-art cross-collection topic modeling, our model achieves up to 13% higher topic coherence, up to 4% bettŠer perplexity, and up to 31% higher document classification accuracy. More importantly, our approach is the €first topic model that ensures disjunct general and€ specific word distributions, resulting in clear-cut topic representations.