According to common relevance-judgments regimes, such as TREC's, a document can be deemed relevant to a query even if it contains a very short passage of text with pertinent information. This fact has motivated work on passage-based document retrieval: document ranking methods that induce information from the document's passages. However, the main source of passage-based information utilized was passage-query similarities. We address the challenge of utilizing richer sources of passage-based information to improve document retrieval effectiveness. Specifically, we devise a suite of learning-to-rank-based document retrieval methods that utilize an effective ranking of passages produced in response to the query; the passage ranking is also induced using a learning-to-rank approach. Some of the methods quantify the ranking of the passages of a document. Others utilize the feature-based representation of passages used for learning a passage ranker. Empirical evaluation attests to the clear merits of our methods with respect to highly effective baselines. Our best performing method is based on learning a document ranking function using document-query features and passage-query features of the document's passage most highly ranked.
Passage-based retrieval models have been studied for some time and have been shown to have some benefits for document ranking. Finding passages that are not only topically relevant, but are also answers to the users' questions would have a significant impact in applications such as mobile search. To develop models for answer passage retrieval, we need to have appropriate test collections and evaluation measures. Making annotations at the passage level is, however, expensive and can have poor coverage. In this paper, we describe the advantages of document summarization measures for evaluating answer passage retrieval and show that these measures have high correlation with existing measures and human judgments. Incorporating conventional, unsupervised features into a neural architecture has the potential to improve modeling effectiveness, but this aspect is often overlooked in the research of deep learning models for information retrieval. We investigate this incorporation in the context of answer sentence selection, and show that combining a set of query matching, readability, and query focus features into a simple convolutional neural network can lead to markedly increased effectiveness. Our results on two standard question-answering datasets show the effectiveness of the combined model. We present a novel contextualization approach for passage retrieval. The core principle is to let any occurrence of a query term in a document affect the passage retrieval score, whether the occurrence is in the passage or not. This effect is controlled by the distance between the term occurrence and the passage. Empirical evaluation demonstrates the merits of our approach; the resultant retrieval performance substantially transcends that of previously proposed passage retrieval methods, including those that use various contextualization approaches. Large collections of full-text documents are now commonly used in automated information retrieval. When the stored document texts are long, the retrieval of complete documents may not be in the users' best interest. In such circumstance, efficient and effective retrieval results may be obtained by using passage retrieval strategies designed to retrieve text excerpts of varying size in response to statements of user interest. New approaches are described in this study for implementing selective passage retrieval systems, and identifying text passages responsive to particular user needs. An automated encyclopedia search system is used to evaluate the usefulness of the proposed methods. An important challenge in cluster-based document retrieval is ranking document clusters by their relevance to the query. We present a novel cluster ranking approach that utilizes Markov Random Fields (MRFs). MRFs enable the integration of various types of cluster-relevance evidence; e.g., the query-similarity values of the cluster's documents and query-independent measures of the cluster. We use our method to re-rank an initially retrieved document list by ranking clusters that are created from the documents most highly ranked in the list. The resultant retrieval effectiveness is substantially better than that of the initial list for several lists that are produced by effective retrieval methods. Furthermore, our cluster ranking approach significantly outperforms state-of- the-art cluster ranking methods. We also show that our method can be used to improve the performance of (state-of- the-art) results-diversification methods. UIUC participated in the HARD track in TREC 2004 and focused on the evaluation of a new method for identifying variable-length passages using HMMs. Most existing approaches to passage retrieval rely on pre-segmentation of documents, but the optimal boundaries of a relevant passage depends on both the query and the document. Our new method aims at determining or improving the boundaries of a relevant passage based on both the query and topical coherence in the document. In this paper, we describe the method and present analysis of our HARD 2004 evaluation results. The results show that the HMM method can improve the boundaries of pre-segmented passages in terms of overall passage retrieval accuracy and recall, but at the price of precision sometimes. However, due to the non-optimality of the relevance feedback procedure and the poor ranking performance based on passage scoring, the best of our passage runs is still worse than a whole document baseline run. Further experiments and analysis are needed to fully understand why the language modeling approach did not work well on passage scoring. Retrieving topically-relevant text passages in documents has been studied many times, but finding non-factoid, multiple sentence answers to web queries is a different task that is becoming increasingly important for applications such as mobile search. As the first stage of developing retrieval models for "answer passages", we describe the process of creating a test collection of questions and multiple-sentence answers based on the TREC GOV2 queries and documents. This annotation shows that most of the description-length TREC queries do in fact have passage-level answers. We then examine the effectiveness of current passage retrieval models in terms of finding passages that contain answers. We show that the existing methods are not effective for this task, and also observe that the relative performance of these methods in retrieving answers does not correspond to their performance in retrieving relevant documents.