FROM USER-GENERATED-CONTENT TO STRUCTURED KNOWLEDGE EXPLORING MULTI-ASPECT SENTENCE REPRESENTATION AND PROTOTYPE HIERARCHY BASED CATEGORIZATION FOR ORGANIZATION OF TEXT COLLECTIONS

Ph.DDOCTOR OF PHILOSOPH

Diversified query expansion

La diversification des résultats de recherche (DRR) vise à sélectionner divers documents à partir des résultats de recherche afin de couvrir autant d’intentions que possible. Dans les approches existantes, on suppose que les résultats initiaux sont suffisamment diversifiés et couvrent bien les aspects de la requête. Or, on observe souvent que les résultats initiaux n’arrivent pas à couvrir certains aspects. Dans cette thèse, nous proposons une nouvelle approche de DRR qui consiste à diversifier l’expansion de requête (DER) afin d’avoir une meilleure couverture des aspects. Les termes d’expansion sont sélectionnés à partir d’une ou de plusieurs ressource(s) suivant le principe de pertinence marginale maximale. Dans notre première contribution, nous proposons une méthode pour DER au niveau des termes où la similarité entre les termes est mesurée superficiellement à l’aide des ressources. Quand plusieurs ressources sont utilisées pour DER, elles ont été uniformément combinées dans la littérature, ce qui permet d’ignorer la contribution individuelle de chaque ressource par rapport à la requête. Dans la seconde contribution de cette thèse, nous proposons une nouvelle méthode de pondération de ressources selon la requête. Notre méthode utilise un ensemble de caractéristiques qui sont intégrées à un modèle de régression linéaire, et génère à partir de chaque ressource un nombre de termes d’expansion proportionnellement au poids de cette ressource. Les méthodes proposées pour DER se concentrent sur l’élimination de la redondance entre les termes d’expansion sans se soucier si les termes sélectionnés couvrent effectivement les différents aspects de la requête. Pour pallier à cet inconvénient, nous introduisons dans la troisième contribution de cette thèse une nouvelle méthode pour DER au niveau des aspects. Notre méthode est entraînée de façon supervisée selon le principe que les termes reliés doivent correspondre au même aspect. Cette méthode permet de sélectionner des termes d’expansion à un niveau sémantique latent afin de couvrir autant que possible différents aspects de la requête. De plus, cette méthode autorise l’intégration de plusieurs ressources afin de suggérer des termes d’expansion, et supporte l’intégration de plusieurs contraintes telles que la contrainte de dispersion. Nous évaluons nos méthodes à l’aide des données de ClueWeb09B et de trois collections de requêtes de TRECWeb track et montrons l’utilité de nos approches par rapport aux méthodes existantes.Search Result Diversification (SRD) aims to select diverse documents from the search results in order to cover as many search intents as possible. For the existing approaches, a prerequisite is that the initial retrieval results contain diverse documents and ensure a good coverage of the query aspects. In this thesis, we investigate a new approach to SRD by diversifying the query, namely diversified query expansion (DQE). Expansion terms are selected either from a single resource or from multiple resources following the Maximal Marginal Relevance principle. In the first contribution, we propose a new term-level DQE method in which word similarity is determined at the surface (term) level based on the resources. When different resources are used for the purpose of DQE, they are combined in a uniform way, thus totally ignoring the contribution differences among resources. In practice the usefulness of a resource greatly changes depending on the query. In the second contribution, we propose a new method of query level resource weighting for DQE. Our method is based on a set of features which are integrated into a linear regression model and generates for a resource a number of expansion candidates that is proportional to the weight of that resource. Existing DQE methods focus on removing the redundancy among selected expansion terms and no attention has been paid on how well the selected expansion terms can indeed cover the query aspects. Consequently, it is not clear how we can cope with the semantic relations between terms. To overcome this drawback, our third contribution in this thesis aims to introduce a novel method for aspect-level DQE which relies on an explicit modeling of query aspects based on embedding. Our method (called latent semantic aspect embedding) is trained in a supervised manner according to the principle that related terms should correspond to the same aspects. This method allows us to select expansion terms at a latent semantic level in order to cover as much as possible the aspects of a given query. In addition, this method also incorporates several different external resources to suggest potential expansion terms, and supports several constraints, such as the sparsity constraint. We evaluate our methods using ClueWeb09B dataset and three query sets from TRECWeb tracks, and show the usefulness of our proposed approaches compared to the state-of-the-art approaches

Beyond Question Answering: Understanding the Information Need of the User

Intelligent interaction between humans and computers has been a dream of artificial intelligence since the beginning of digital era and one of the original motivations behind the creation of artificial intelligence. A key step towards the achievement of such an ambitious goal is to enable the Question Answering systems understand the information need of the user. In this thesis, we attempt to enable the QA system's ability to understand the user's information need by three approaches. First, an clarification question generation method is proposed to help the user clarify the information need and bridge information need gap between QA system and the user. Next, a translation based model is obtained from the large archives of Community Question Answering data, to model the information need behind a question and boost the performance of question recommendation. Finally, a fine-grained classification framework is proposed to enable the systems to recommend answered questions based on information need satisfaction

Methods for ranking user-generated text streams: a case study in blog feed retrieval

User generated content are one of the main sources of information on the Web nowadays. With the huge amount of this type of data being generated everyday, having an efficient and effective retrieval system is essential. The goal of such a retrieval system is to enable users to search through this data and retrieve documents relevant to their information needs. Among the different retrieval tasks of user generated content, retrieving and ranking streams is one of the important ones that has various applications. The goal of this task is to rank streams, as collections of documents with chronological order, in response to a user query. This is different than traditional retrieval tasks where the goal is to rank single documents and temporal properties are less important in the ranking. In this thesis we investigate the problem of ranking user-generated streams with a case study in blog feed retrieval. Blogs, like all other user generated streams, have specific properties and require new considerations in the retrieval methods. Blog feed retrieval can be defined as retrieving blogs with a recurrent interest in the topic of the given query. We define three different properties of blog feed retrieval each of which introduces new challenges in the ranking task. These properties include: 1) term mismatch in blog retrieval, 2) evolution of topics in blogs and 3) diversity of blog posts. For each of these properties, we investigate its corresponding challenges and propose solutions to overcome those challenges. We further analyze the effect of our solutions on the performance of a retrieval system. We show that taking the new properties into account for developing the retrieval system can help us to improve state of the art retrieval methods. In all the proposed methods, we specifically pay attention to temporal properties that we believe are important information in any type of streams. We show that when combined with content-based information, temporal information can be useful in different situations. Although we apply our methods to blog feed retrieval, they are mostly general methods that are applicable to similar stream ranking problems like ranking experts or ranking twitter users

Concept-based Text Clustering

Thematic organization of text is a natural practice of humans and a crucial task for today's vast repositories. Clustering automates this by assessing the similarity between texts and organizing them accordingly, grouping like ones together and separating those with different topics. Clusters provide a comprehensive logical structure that facilitates exploration, search and interpretation of current texts, as well as organization of future ones. Automatic clustering is usually based on words. Text is represented by the words it mentions, and thematic similarity is based on the proportion of words that texts have in common. The resulting bag-of-words model is semantically ambiguous and undesirably orthogonal|it ignores the connections between words. This thesis claims that using concepts as the basis of clustering can significantly improve effectiveness. Concepts are defined as units of knowledge. When organized according to the relations among them, they form a concept system. Two concept systems are used here: WordNet, which focuses on word knowledge, and Wikipedia, which encompasses world knowledge. We investigate a clustering procedure with three components: using concepts to represent text; taking the semantic relations among them into account during clustering; and learning a text similarity measure from concepts and their relations. First, we demonstrate that concepts provide a succinct and informative representation of the themes in text, exemplifying this with the two concept systems. Second, we define methods for utilizing concept relations to enhance clustering by making the representation models more discriminative and extending thematic similarity beyond surface overlap. Third, we present a similarity measure based on concepts and their relations that is learned from a small number of examples, and show that it both predicts similarity consistently with human judgement and improves clustering. The thesis provides strong support for the use of concept-based representations instead of the classic bag-of-words model

Combination Methods for Automatic Document Organization

Automatic document classification and clustering are useful for a wide range of applications such as organizing Web, intranet, or portal pages into topic directories, filtering news feeds or mail, focused crawling on the Web or in intranets, and many more. This thesis presents ensemble-based meta methods for supervised learning (i.e., classification based on a small amount of hand-annotated training documents). In addition, we show how these techniques can be carried forward to clustering based on unsupervised learning (i.e., automatic structuring of document corpora without training data). The algorithms are applied in a restrictive manner, i.e., by leaving out some \u27uncertain\u27 documents (rather than assigning them to inappropriate topics or clusters with low confidence). We show how restrictive meta methods can be used to combine different document representations in the context of Web document classification and author recognition. As another application for meta methods we study the combination of difierent information sources in distributed environments, such as peer-to-peer information systems. Furthermore we address the problem of semi-supervised classification on document collections using retraining. A possible application is focused Web crawling which may start with very few, manually selected, training documents but can be enhanced by automatically adding initially unlabeled, positively classified Web pages for retraining. The results of our systematic evaluation on real world data show the viability of the proposed approaches.Automatische Dokumentklassifikation und Clustering sind für eine Vielzahl von Anwendungen von Bedeutung, wie beispielsweise Organisation von Web-, Intranet- oder Portalseiten in thematische Verzeichnisse, Filterung von Nachrichtenmeldungen oder Emails, fokussiertes Crawling im Web oder in Intranets und vieles mehr. Diese Arbeit untersucht Ensemble-basierte Metamethoden für Supervised Learning (d.h. Klassifikation basierend auf einer kleinen Anzahl von manuell annotierten Trainingsdokumenten). Weiterhin zeigen wir, wie sich diese Techniken auf Clustering basierend auf Unsupervised Learning (d.h. die automatische Strukturierung von Dokumentkorpora ohne Trainingsdaten) übertragen lassen. Dabei wenden wir die Algorithmen in restriktiver Form an, d.h. wir treffen keine Aussage über eine Teilmenge von "unsicheren" Dokumenten (anstatt sie mit niedriger Konfidenz ungeeigneten Themen oder Clustern zuzuordnen). Wir verwendenen restriktive Metamethoden um unterschiedliche Dokumentrepräsentationen, im Kontext der Klassifikation von Webdokumentem und der Autorenerkennung, miteinander zu kombinieren. Als weitere Anwendung von Metamethoden untersuchen wir die Kombination von unterschiedlichen Informationsquellen in verteilten Umgebungen wie Peer-to-Peer Informationssystemen. Weiterhin betrachten wir das Problem der Semi-Supervised Klassifikation von Dokumentsammlungen durch Retraining. Eine mögliche Anwendung ist fokussiertesWeb Crawling, wo wir mit sehr wenigen, manuell ausgewählten Trainingsdokumenten starten, die durch Hinzufugen von ursprünglich nicht klassifizierten Dokumenten ergänzt werden. Die Resultate unserer systematischen Evaluation auf realen Daten zeigen das gute Leistungsverhalten unserer Methoden

A Proportionality-based Approach to Search Result Diversification

Search result diversification addresses the problem of queries with unclear information needs. The aim of using diversification techniques is to find a ranking of documents that covers multiple possible interpretations, aspects, or topics for a given query. By explicitly providing diversity in search results, this approach can increase the likelihood that users will find documents relevant to their specific intent, thereby improving effectiveness. This dissertation introduces a new perspective on diversity: diversity by proportionality. We consider a result list more diverse, with respect to some set of topics related to the query, when the ratio between the number of relevant documents it provides for each of these topics matches more closely with the topic popularity distribution. Consequently, we derive an effectiveness measure based on proportionality and propose a new framework for optimizing proportionality in search results, which we show to be more effective than existing techniques. Diversification would be impractical without the ability to automatically infer the set of topics associated with the user queries. Therefore, we study cluster-based techniques for generating these topics from publicly available data sources. Based on the challenges that we observe with topic generation, we present a simplified term-based representation for query topics. Specifically, we propose to identify for each query a single set of terms that describes its topics. This set is provided to a diversification technique which in effect treats each of the terms as a topic to determine coverage in the search results. We call this approach term level diversification and we show that it can promote diversity with respect to the topics underlying the input terms. This simplifies the task of finding a set of query topics, which has proven difficult, to finding only a set of terms. We also present a technique as well as several data sources for generating these terms effectively