The Document Representation Problem: An Analysis of LSI and IterativeResidual Rescaling
Important text analysis problems in information retrieval and natural language processing, such as document clustering and automatic text summarization, require accurate measurement of inter-document similarity. The goal of this work is to find methods for automatically creating document representations in which inter-document similarity measurements correspond to human judgment. We present a new model for the task of creating document representations. From this model, we derive a new analysis of Latent Semantic Indexing (LSI), which is one of the successful approaches that has been studied extensively. In particular, we show a precise relationship between LSI's performance and the uniformity of the underlying distribution of documents over topics. As a consequence, we propose a novel alternative method called Iterative Residual Rescaling (IRR), that, crucially, compensates for distributional non-uniformity. Experiments over a variety of practically-encountered settings and with several evaluation metrics validate our theoretical prediction and confirm the effectiveness of IRR in comparison to LSI. We also propose several extensions including a new document sampling method to scale IRR up to large document collections. Comparison with random sampling provides further empirical evidence that performance can be improved by counteracting non-uniformity. Finally, we present a system for multi-document summarization based on IRR, which demonstrates that IRR can be immediately useful in applications. We show that IRR works as a framework to find a tightly connected (and therefore interpretable) set of coherent texts, and effectively present them to the user.
computer science; technical report
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