A corpus study of verbal multiword expressions in Brazilian Portuguese

Verbal multiword expressions (VMWEs) such as to make ends meet require special attention in NLP and linguistic research, and annotated corpora are valuable resources for studying them. Corpora annotated with VMWEs in several languages, including Brazilian Portuguese, were made freely available in the PARSEME shared task. The goal of this paper is to describe and analyze this corpus in terms of the characteristics of annotated VMWEs in Brazilian Portuguese. First, we summarize and exemplify the criteria used to annotate VMWEs. Then, we analyze their frequency, average length, discontinuities and variability. We further discuss challenging constructions and borderline cases. We believe that this analysis can improve the annotated corpus and its results can be used to develop systems for automatic VMWE identification

Acronyms as an integral part of multi–word term recognition - A token of appreciation

Term conflation is the process of linking together different variants of the same term. In automatic term recognition approaches, all term variants should be aggregated into a single normalized term representative, which is associated with a single domain–specific concept as a latent variable. In a previous study, we described FlexiTerm, an unsupervised method for recognition of multi–word terms from a domain–specific corpus. It uses a range of methods to normalize three types of term variation – orthographic, morphological and syntactic variation. Acronyms, which represent a highly productive type of term variation, were not supported. In this study, we describe how the functionality of FlexiTerm has been extended to recognize acronyms and incorporate them into the term conflation process. The main contribution of this study is not acronym recognition per se, but rather its integration with other types of term variation into the term conflation process. We evaluated the effects of term conflation in the context of information retrieval as one of its most prominent applications. On average, relative recall increased by 32 percent points, whereas index compression factor increased by 7 percent points. Therefore, evidence suggests that integration of acronyms provides non–trivial improvement of term conflation

Termos, relacionamentos e representatividade na indexação de texto para recuperação de informação

Uma das fases da recuperação de informação é a indexação dos textos dos documentos. Nesta fase, um conjunto de descritores (termos e/ou relacionamentos entre termos) descreve conceitos (atômicos e/ou complexos) presentes nos textos. Diversas estratégias com tais finalidades são encontrados na bibliografia, algumas consideram dependência de termos e outras não. Com o objetivo de apresentar uma visão geral das estratégias de representação de textos que consideram dependência de termos, são descritas quatro experiências onde as representatividades dos relacionamentos dependem dos termos componentes (estratégias com índices múltiplos, com árvore binária, com triplas e com famílias morfológicas), três onde as representatividades dos relacionamentos dependem de suas próprias freqüências de ocorrência (estratégias com expressões de índice, com pares lematizados e com expressões ternárias), duas onde os relacionamentos são reconhecidos mas não são utilizados como descritores (estratégias com nodos temáticos e com conexões gramaticais) e uma experiência onde os relacionamentos são eminentemente estatísticos (estratégia com bitermos)

Information Extraction from Text for Improving Research on Small Molecules and Histone Modifications

The cumulative number of publications, in particular in the life sciences, requires efficient methods for the automated extraction of information and semantic information retrieval. The recognition and identification of information-carrying units in text – concept denominations and named entities – relevant to a certain domain is a fundamental step. The focus of this thesis lies on the recognition of chemical entities and the new biological named entity type histone modifications, which are both important in the field of drug discovery. As the emergence of new research fields as well as the discovery and generation of novel entities goes along with the coinage of new terms, the perpetual adaptation of respective named entity recognition approaches to new domains is an important step for information extraction. Two methodologies have been investigated in this concern: the state-of-the-art machine learning method, Conditional Random Fields (CRF), and an approximate string search method based on dictionaries. Recognition methods that rely on dictionaries are strongly dependent on the availability of entity terminology collections as well as on its quality. In the case of chemical entities the terminology is distributed over more than 7 publicly available data sources. The join of entries and accompanied terminology from selected resources enables the generation of a new dictionary comprising chemical named entities. Combined with the automatic processing of respective terminology – the dictionary curation – the recognition performance reached an F1 measure of 0.54. That is an improvement by 29 % in comparison to the raw dictionary. The highest recall was achieved for the class of TRIVIAL-names with 0.79. The recognition and identification of chemical named entities provides a prerequisite for the extraction of related pharmacological relevant information from literature data. Therefore, lexico-syntactic patterns were defined that support the automated extraction of hypernymic phrases comprising pharmacological function terminology related to chemical compounds. It was shown that 29-50 % of the automatically extracted terms can be proposed for novel functional annotation of chemical entities provided by the reference database DrugBank. Furthermore, they are a basis for building up concept hierarchies and ontologies or for extending existing ones. Successively, the pharmacological function and biological activity concepts obtained from text were included into a novel descriptor for chemical compounds. Its successful application for the prediction of pharmacological function of molecules and the extension of chemical classification schemes, such as the the Anatomical Therapeutic Chemical (ATC), is demonstrated. In contrast to chemical entities, no comprehensive terminology resource has been available for histone modifications. Thus, histone modification concept terminology was primary recognized in text via CRFs with a F1 measure of 0.86. Subsequent, linguistic variants of extracted histone modification terms were mapped to standard representations that were organized into a newly assembled histone modification hierarchy. The mapping was accomplished by a novel developed term mapping approach described in the thesis. The combination of term recognition and term variant resolution builds up a new procedure for the assembly of novel terminology collections. It supports the generation of a term list that is applicable in dictionary-based methods. For the recognition of histone modification in text it could be shown that the named entity recognition method based on dictionaries is superior to the used machine learning approach. In conclusion, the present thesis provides techniques which enable an enhanced utilization of textual data, hence, supporting research in epigenomics and drug discovery

Representation and Processing of Composition, Variation and Approximation in Language Resources and Tools

In my habilitation dissertation, meant to validate my capacity of and maturity for directingresearch activities, I present a panorama of several topics in computational linguistics, linguisticsand computer science.Over the past decade, I was notably concerned with the phenomena of compositionalityand variability of linguistic objects. I illustrate the advantages of a compositional approachto the language in the domain of emotion detection and I explain how some linguistic objects,most prominently multi-word expressions, defy the compositionality principles. I demonstratethat the complex properties of MWEs, notably variability, are partially regular and partiallyidiosyncratic. This fact places the MWEs on the frontiers between different levels of linguisticprocessing, such as lexicon and syntax.I show the highly heterogeneous nature of MWEs by citing their two existing taxonomies.After an extensive state-of-the art study of MWE description and processing, I summarizeMultiflex, a formalism and a tool for lexical high-quality morphosyntactic description of MWUs.It uses a graph-based approach in which the inflection of a MWU is expressed in function ofthe morphology of its components, and of morphosyntactic transformation patterns. Due tounification the inflection paradigms are represented compactly. Orthographic, inflectional andsyntactic variants are treated within the same framework. The proposal is multilingual: it hasbeen tested on six European languages of three different origins (Germanic, Romance and Slavic),I believe that many others can also be successfully covered. Multiflex proves interoperable. Itadapts to different morphological language models, token boundary definitions, and underlyingmodules for the morphology of single words. It has been applied to the creation and enrichmentof linguistic resources, as well as to morphosyntactic analysis and generation. It can be integratedinto other NLP applications requiring the conflation of different surface realizations of the sameconcept.Another chapter of my activity concerns named entities, most of which are particular types ofMWEs. Their rich semantic load turned them into a hot topic in the NLP community, which isdocumented in my state-of-the art survey. I present the main assumptions, processes and resultsissued from large annotation tasks at two levels (for named entities and for coreference), parts ofthe National Corpus of Polish construction. I have also contributed to the development of bothrule-based and probabilistic named entity recognition tools, and to an automated enrichment ofProlexbase, a large multilingual database of proper names, from open sources.With respect to multi-word expressions, named entities and coreference mentions, I pay aspecial attention to nested structures. This problem sheds new light on the treatment of complexlinguistic units in NLP. When these units start being modeled as trees (or, more generally, asacyclic graphs) rather than as flat sequences of tokens, long-distance dependencies, discontinu-ities, overlapping and other frequent linguistic properties become easier to represent. This callsfor more complex processing methods which control larger contexts than what usually happensin sequential processing. Thus, both named entity recognition and coreference resolution comesvery close to parsing, and named entities or mentions with their nested structures are analogous3to multi-word expressions with embedded complements.My parallel activity concerns finite-state methods for natural language and XML processing.My main contribution in this field, co-authored with 2 colleagues, is the first full-fledged methodfor tree-to-language correction, and more precisely for correcting XML documents with respectto a DTD. We have also produced interesting results in incremental finite-state algorithmics,particularly relevant to data evolution contexts such as dynamic vocabularies or user updates.Multilingualism is the leitmotif of my research. I have applied my methods to several naturallanguages, most importantly to Polish, Serbian, English and French. I have been among theinitiators of a highly multilingual European scientific network dedicated to parsing and multi-word expressions. I have used multilingual linguistic data in experimental studies. I believethat it is particularly worthwhile to design NLP solutions taking declension-rich (e.g. Slavic)languages into account, since this leads to more universal solutions, at least as far as nominalconstructions (MWUs, NEs, mentions) are concerned. For instance, when Multiflex had beendeveloped with Polish in mind it could be applied as such to French, English, Serbian and Greek.Also, a French-Serbian collaboration led to substantial modifications in morphological modelingin Prolexbase in its early development stages. This allowed for its later application to Polishwith very few adaptations of the existing model. Other researchers also stress the advantages ofNLP studies on highly inflected languages since their morphology encodes much more syntacticinformation than is the case e.g. in English.In this dissertation I am also supposed to demonstrate my ability of playing an active rolein shaping the scientific landscape, on a local, national and international scale. I describemy: (i) various scientific collaborations and supervision activities, (ii) roles in over 10 regional,national and international projects, (iii) responsibilities in collective bodies such as program andorganizing committees of conferences and workshops, PhD juries, and the National UniversityCouncil (CNU), (iv) activity as an evaluator and a reviewer of European collaborative projects.The issues addressed in this dissertation open interesting scientific perspectives, in whicha special impact is put on links among various domains and communities. These perspectivesinclude: (i) integrating fine-grained language data into the linked open data, (ii) deep parsingof multi-word expressions, (iii) modeling multi-word expression identification in a treebank as atree-to-language correction problem, and (iv) a taxonomy and an experimental benchmark fortree-to-language correction approaches

Finding answers to definition questions on the web

Fundamentally, question answering systems are designed for automatically responding to queries posed by users in natural language. The first step in the answering process is query analysis, and its goal is to classify the query in concert with a set of pre-specified types. Traditionally, these classes include: factoid, definition, and list. Systems thereafter chose the answering method in congruence with the class recognised in this early phase. In short, this thesis focuses exclusively on strategies to tackle definition questions (e.g.\u27; Who is Ben Bernanke?"). This sort of question has become especially interesting in recent years, due to its significant number of submissions to search engines. Most advances in definition question answering have been made under the umbrella of the Text REtrieval Conference (TREC). This is, more precisely, a framework for testing systems operating on a collection of news articles. Thus, the objective of chapter one is to describe this framework along with presenting additional introductory aspects of definition question answering including: (a) how definition questions are prompted by individuals; (b) the different conceptions of definition, and thus of answers; and (c) the various metrics exploited for assessing systems. Since the inception of TREC, systems have put to the test manifold approaches to discover answers, throwing some light onto several key aspects of this problem. On this account, chapter four goes over a selection of some notable TREC systems. This selection is not aimed at completeness, but rather at highlighting the leading features of these systems. For the most part, systems benefit from knowledge bases (e.g., Wikipedia) for obtaining descriptions about the concept being defined (a.k.a. definiendum). These descriptions are thereafter projected onto the array of candidate answers as a means of discerning the correct answer. In other words, these knowledge bases play the role of annotated resources, and most systems attempt to find the answer candidates across the collection of news articles that are more similar to these descriptions. The cornerstone of this thesis is the assumption that it is plausible to devise competitive, and hopefully better, systems without the necessity of annotated resources. Although this descriptive knowledge is helpful, it is the belief of the author that they are built on two wrong premises: 1.It is arguable that senses or contexts related to the definiendum across knowledge bases are the same senses or contexts for the instances across the array of answer candidates. This observation also extends to the fact that not all descriptions within the group of putative answers are necessarily covered by knowledge bases, even though they might refer to the same contexts or senses. 2.Finding an efficient projection strategy does not necessarily entail a good procedure for discerning descriptive knowledge, because it shifts the goal of the task to a more like this set" instead of analysing whether or not each candidate bears the characteristics of a description. In other words, the coverage given by knowledge bases for a specific definiendum is not wide enough to learn all the characteristics that typify its descriptions, so that systems are capable of identifying all answers within the set of candidates. From another angle, a conventional projection methodology can be seen as a finder of lexical analogies. All in all, this thesis investigates into models that disregard this kind of annotated resource and projection strategy. In effect, it is the belief of the author that a robust technique of this sort can be integrated with traditional projection methodologies, and in this way bringing about an enhancement in performance. The major contributions of this thesis are presented in chapters five, six and seven. There are several ways of understanding this structure. For example, chapter five presents a general framework for answering definition questions in several languages. The primary goal of this study is to design a lightweight definition question answering system operating on web-snippets and two languages: English and Spanish. The idea is to utilise web-snippets as a source of descriptive information in several languages, and the high degree of language independency is achieved by making allowances for as little linguistic knowledge as possible. To put it more precisely, this system accounts for statistical methods and a list of stop-words, as well as a set of language-dependent definition patterns. In detail, chapter five branches into two more specific studies. The first study is essentially aimed at capitalising on redundancy for detecting answers (e.g., word frequency counts across answer candidates). Although this type of feature has been widely used by TREC systems, this study focuses on its impact on different languages, and its benefits when applied to web-snippets instead of a collection of news documents. An additional motivation behind targeting web-snippets is the hope of studying systems working on more heterogenous corpora, without incurring the need of downloading full-documents. For instance, on the Internet, the number of distinct senses for the definiendum considerably increases, ergo making it necessary to consider a sense discrimination technique. For this purpose, the system presented in this chapter takes advantage of an unsupervised approach premised on Latent Semantic Analysis. Although the outcome of this study shows that sense discrimination is hard to achieve when operating solely on web snippets, it also reveals that they are a fruitful source of descriptive knowledge, and that their extraction poses exciting challenges. The second branch extends this first study by exploiting multilingual knowledge bases (i.e. Wikipedia) for ranking putative answers. Generally speaking, it makes use of word association norms deduced from sentences that match definitions patterns across Wikipedia. In order to adhere to the premise of not profiting from articles related to a specific definiendum, these sentences are anonymised by replacing the concept with a placeholder, and the word norms are learnt from all training sentences, instead of only from the Wikipedia page about the particular definiendum. The results of this study signify that this use of these resources can also be beneficial; in particular, they reveal that word association norms are a cost-efficient solution. However, the size of the corpus markedly decreases for languages different from English, thus indicating their insufficiency to design models for other languages. Later, chapter six gets more specific and deals only with the ranking of answer candidates in English. The reason for abandoning the idea of Spanish is the sparseness observed across both the redundancy from the Internet and the training material mined from Wikipedia. This sparseness is considerably greater than in the case of English, and it makes learning powerful statistical models more difficult. This chapter presents a novel way of modeling definitions grounded on n-gram language models inferred from the lexicalised dependency tree representation of the training material acquired in the study of chapter five. These models are contextual in the sense that they are built in relation to the semantic of the sentence. Generally, these semantics can be perceived as the distinct types of definienda (e.g., footballer, language, artist, disease, and tree). This study, in addition, investigates the effect of some features on these context models (i.e., named entities, and part-of-speech tags). Overall, the results obtained by this approach are encouraging, in particular in terms of increasing the accuracy of the pattern matching. However, in all likelihood, it was experimentally observed that a training corpus comprising only positive examples (descriptions) is not enough to achieve perfect accuracy, because these models cannot deduce the characteristics that typify non-descriptive content. More essential, as future work, context models give the chance to study how different contexts can be amalgamated (smoothed) in agreement with their semantic similarities in order to ameliorate the performance. Subsequently, chapter seven gets even more specific and it searches for the set of properties that can aid in discriminating descriptions from other kinds of texts. Note that this study regards all kinds of descriptions, including those mismatching definition patters. In so doing, Maximum Entropy models are constructed on top of an automatically acquired large-scale training corpus, which encompasses descriptions from Wikipedia and non-descriptions from the Internet. Roughly speaking, different models are constructed as a means of studying the impact of assorted properties: surface, named entities, part-of-speech tags, chunks, and more interestingly, attributes derived from the lexicalised dependency graphs. In general, results corroborate the efficiency of features taken from dependency graphs, especially the root node and n-gram paths. Experiments conducted on testing sets of various characteristics suggest that it is also plausible to find attributes that can port to other corpora. The second and the third are extra chapters. The former examines different strategies to trawl the Web for descriptive knowledge. In essence, this chapter touches on several strategies geared towards boosting the recall of descriptive sentences across web snippets, especially sentences that match widespread definition patterns. This is a side, but instrumental study to the core of this thesis, as it is necessary for systems targeted at the Internet to develop effective crawling techniques. On the contrary, chapter three has two goals: (a) presenting some components used by the strategies outlined in the last three chapters, this way helping to focus on key aspects of the ranking methodologies, and hence to clearly present the relevant aspects of approaches laid out in these three chapters; and (b) fleshing out some characteristics that make separating the genuine from the misleading answer candidates difficult; particularly, across sentences matching definition patterns. Chapter three is helpful for understanding part of the linguistic phenomena that the posterior chapters deal with. On a final note about the organisation of this thesis, since there is a myriad of techniques, chapter six and seven start dissecting the related work closer to each strategy. The main contribution of each chapter begins at section 6.5 and 7.6, respectively. These two sections start with a discussion and comparison between the proposed methods and the related work presented in their corresponding preceding sections. This organisation is directed at facilitating the contextualisation of the proposed approaches as there are different question answering systems with manifold characteristics.Frage-Antwort-Systeme sind im Wesentlichen dafür konzipiert, von Benutzern in natürlicher Sprache gestellte Anfragen automatisiert zu beantworten. Der erste Schritt im Beantwortungsprozess ist die Analyse der Anfrage, deren Ziel es ist, die Anfrage entsprechend einer Menge von vordefinierten Typen zu klassifizieren. Traditionell umfassen diese: Faktoid, Definition und Liste. Danach wählten die Systeme dieser frühen Phase die Antwortmethode entsprechend der zuvor erkannten Klasse. Kurz gesagt konzentriert sich diese Arbeit ausschließlich auf Strategien zur Lösung von Fragen nach Definitionen (z.B. ,,emph{Wer ist Ben Bernanke?}"). Diese Art von Anfrage ist in den letzten Jahren besonders interessant geworden, weil sie in beachtlicher Zahl bei Suchmaschinen eingeht. Die meisten Fortschritte in Bezug auf die Beantwortung von Fragen nach Definitionen wurden unter dem Dach der Text Retrieval Conference (TREC) gemacht. Das ist, genauer gesagt, ein Framework zum Testen von Systemen, die mit einer Auswahl von Zeitungsartikeln arbeiten. Daher, zielt Kapitel eins auf eine Beschreibung dieses Rahmenwerks ab, zusammen mit einer Darstellung weiterer einführender Aspekte der Beantwortung von Definitionsanfragen. Diesen schließen u.a. ein: (a) wie Definitionsanfragen von Personen gestellt werden; (b) die unterschiedlichen Begriffe von Definition und folglich auch Antworten; und (c) die unterschiedlichen Metriken, die zur Bewertung von Systemen genutzt werden. Seit Anbeginn von TREC haben Systeme vielfältige Ansätze, Antworten zu entdecken, auf die Probe gestellt und dabei eine Reihe von zentralen Aspekten dieses Problems beleuchtet. Aus diesem Grund behandelt Kapitel vier eine Auswahl einiger bekannter TREC Systeme. Diese Auswahl zielt nicht auf Vollständigkeit ab, sondern darauf, die wesentlichen Merkmale dieser Systeme hervorzuheben. Zum größten Teil nutzen die Systeme Wissensbasen (wie z.B. Wikipedia), um Beschreibungen des zu definierenden Konzeptes (auch als Definiendum bezeichnet) zu erhalten. Diese Beschreibungen werden danach auf eine Reihe von möglichen Antworten projiziert, um auf diese Art die richtige Antwort zu ermitteln. Anders ausgedrückt nehmen diese Wissensbasen die Funktion von annotierten Ressourcen ein, wobei die meisten Systeme versuchen, die Antwortkandidaten in einer Sammlung von Zeitungsartikeln zu finden, die diesen Beschreibungen ähnlicher sind. Den Grundpfeiler dieser Arbeit bildet die Annahme, dass es plausibel ist, ohne annotierte Ressourcen konkurrenzfähige, und hoffentlich bessere, Systeme zu entwickeln. Obwohl dieses deskriptive Wissen hilfreich ist, basieren sie nach Überzeugung des Autors auf zwei falschen Annahmen: 1. Es ist zweifelhaft, ob die Bedeutungen oder Kontexte, auf die sich das Definiendum bezieht, dieselben sind wie die der Instanzen in der Reihe der Antwortkandidaten. Darüber hinaus erstreckt sich diese Beobachtung auch auf die Tatsache, dass nicht alle Beschreibungen innerhalb der Gruppe der mutmaßlichen Antworten notwendigerweise von Wissensbasen abgedeckt werden, auch wenn sie sich auf dieselben Bedeutungen und Kontexte beziehen. 2. Eine effiziente Projektionsstrategie zu finden bedeutet nicht notwendigerweise auch ein gutes Verfahren zur Feststellung von deskriptivem Wissen, denn es verschiebt die Zielsetzung der Aufgabe hin zu einem ,,mehr wie diese Menge" statt zu analysieren, ob jeder Kandidat den Charakteristika einer Beschreibung entspricht oder nicht. Anders ausgedrückt ist die Abdeckung, die durch Wissensbasen für ein spezifisches Definiendum gegeben ist, nicht umfassend genug, um alle Charakteristika, die für seine Beschreibungen kennzeichnend sind, zu erlernen, so dass die Systeme in der Lage sind, alle Antworten innerhalb der Kandidatenmenge zu identifizieren. Eine konventionelle Projektionsstrategie kann aus einem anderen Blickwinkel als Prozedur zum Finden lexikalischer Analogien betrachtet werden. Insgesamt untersucht diese Arbeit Modelle, die Strategien dieser Art in Verbindung mit annotierten Ressourcen und Projektion außer Acht lassen. Tatsächlich ist es die Überzeugung des Autors, dass eine robuste Technik dieser Art mit traditionellen Methoden der Projektion integriert wird und so eine Leistungssteigerung ermöglichen kann. Die größeren Beiträge dieser Arbeit werden in den Kapiteln fünf, sechs und sieben präsentiert. Es gibt mehrere Wege diese Struktur zu verstehen. Kapitel fünf, beispielsweise, präsentiert einen allgemeinen Rahmen für die Beantwortung von Fragen nach Definitionen in mehreren Sprachen. Das primäre Ziel dieser Studie ist es, ein leichtgewichtiges System zur Beantwortung von Fragen nach Definitionen zu entwickeln, das mit Web-Snippets und zwei Sprachen arbeitet: Englisch und Spanisch. Die Grundidee ist, von Web-Snippets als Quelle deskriptiver Information in mehreren Sprachen zu profitieren, wobei der hohe Grad an Sprachunabhängigkeit dadurch erreicht wird, dass so wenig linguistisches Wissen wie möglich berücksichtigt wird. Genauer gesagt berücksichtigt dieses System statistische Methoden und eine Liste von Stop-Wörtern sowie eine Reihe von sprach-spezifischen Definitionsmustern. Im Einzelnen teilt sich Kapitel fünf in zwei spezifischere Studien auf. Die erste Studie zielt im Grunde darauf ab, aus Redundanz für die Ermittlung von Antworten Kapital zu schlagen (z.B. Worthäufigkeiten über verschiedene Antwortkandidaten hinweg). Obwohl eine solche Eigenschaft unter TREC Systemen weit verbreitet ist, legt diese Studie den Schwerpunkt auf die Auswirkungen auf verschiedene Sprachen und auf ihre Vorteile bei der Anwendung auf Web-Snippets statt Zeitungsartikeln. Eine weitere Motivation dahinter, Web-Snippets ins Auge zu fassen, ist die Hoffnung, Systeme zu studieren, die mit heterogenen Corpora arbeiten, ohne es nötig zu machen, vollständige Dokumente herunter zu laden. Im Internet, beispielsweise, steigt die Zahl verschiedener Bedeutungen für das Definiendum deutlich an, was es notwendig macht, eine Technik zur Unterscheidung von Bedeutungen in Betracht zu ziehen. Zu diesem Zweck nutzt das System, das in diesem Kapitel vorgestellt wird, einen unüberwachten Ansatz, der auf der Latent Semantic Analysis basiert. Auch wenn das Ergebnis dieser Studie zeigt, dass die Unterscheidung von Bedeutungen allein anhand von Web-Snippets schwer zu erreichen ist, so lässt es doch auch erkennen, dass sie eine fruchtbare Quelle deskriptiven Wissens darstellen und dass ihre Extraktion spannende Herausforderungen bereithält. Der zweite Teil erweitert diese erste Studie durch die Nutzung mehrsprachiger Wissensbasen (d.h. Wikipedia), um die möglichen Antworten in eine Rangfolge einzureihen. Allgemein ausgedrückt profitiert sie von Wortassoziationsnormen, die von Sätzen gelernt werden, die über Wikipedia hinweg zu Definitionsmustern passen. Um an der Prämisse festzuhalten, keine Artikel mit Bezug auf eine spezifisches Definiendum zu nutzen, werden diese Sätze anonymisiert, indem der Begriff mit einem Platzhalter ersetzt wird, und die Wortnormen werden von allen Sätzen der Trainingsmenge gelernt, statt nur von dem Wikipedia-Artikel, der sich auf das spezielle Definiendum bezieht. Die Ergebnisse dieser Studie zeigen, dass diese Nutzung dieser Ressourcen ebenfalls vorteilhaft sein kann; speziell zeigen sie auf, dass Wortassoziationsnormen eine kosteneffiziente Lösung darstellen. Allerdings nehmen die Corpusgrößen über andere Sprachen als Englisch deutlich ab, was auf deren Unzulänglichkeit für die Konstruktion von Modellen für andere Sprachen hinweist. Kapitel sechs, weiter hinten, wird spezieller und handelt ausschließlich von der Einordnung von Antwortkandidaten in englischer Sprache in eine Rangfolge. Der Grund dafür, hier Spanisch außer Acht zu lassen, ist die geringe beobachtete Dichte, sowohl in Bezug auf redundante Information im Internet als auch in Bezug auf Trainingsmaterial, das von Wikipedia erworben wurde. Diese geringe Dichte ist deutlich stärker ausgeprägt als im Fall der englischen Sprache und erschwert das Erlernen mächtiger statischer Modelle. Dieses Kapitel präsentiert einen neuartigen Weg, Definitionen zu modellieren, die in n-gram Sprachmodellen verankert sind, die aus der lexikalisierten Darstellung des Abhängigkeitsbaumes des in Kapitel fünf erworbenen Trainingsmaterials gelernt wurden. Diese Modelle sind kontextuell in dem Sinne, dass sie in Bezug auf die Semantikdes Satzes konstruiert werden. Im Allgemeinen können diese Semantiken als unterschiedliche Typen von Definienda betrachtet werden (z.B. Fußballer, Sprache, Künstler, Krankheit und Baum). Diese Studie untersucht zusätzlich die Auswirkungen einiger Eigenschaften (nämlich benannter Entitäten und Part-of-speech-Tags) auf diese Kontextmodelle. Insgesamt sind die Ergebnisse, die mit diesem Ansatz erhalten wurden, ermutigend, insbesondere in Bezug auf eine Steigerung der Genauigkeit des Musterabgleichs. Indes wurde höchstwahrscheinlich experimentell beobachtet, dass ein Trainingscorpus, das nur Positivbeispiele (Beschreibungen) enthält, nicht ausreicht, um perfekte Genauigkeit zu erreichen, da diese Modelle die Charakteristika nicht ableiten können, die für nicht-deskriptiven Inhalt kennzeichnend sind. Für die weitere Arbeit ermöglichen es Kontextmodelle zu untersuchen, wie unterschiedliche Kontexte in Übereinstimmung mit deren semantischen Ähnlichkeiten verschmolzen (geglättet) werden können, um die Leistung zu verstärken. Kapitel sieben wird anschließend sogar noch spezieller und sucht nach der Menge von Eigenschaften, die dabei helfen kann, Beschreibungen von anderen Textarten zu unterscheiden. Dabei sollte beachtet werden, dass diese Studie alle Arten von Beschreibungen berücksichtigt, einschließlich derer, die Definitionsmustern nicht genügen. Dadurch werden Maximum-Entropy-Modelle konstruiert, die auf einen automatisch akquirierten Corpus von großem Umfang aufsetzen, der Beschreibungen von Wikipedia und Nicht-Beschreibungen aus dem Internet umfasst. Grob gesagt werden unterschiedliche Modelle konstruiert, um die Auswirkungen verschiedenerlei Merkmale zu untersuchen: Oberfläche, benannte Entitäten, Part-of-speech-Tags, Chunks und, noch interessanter, von den lexikalisierten Abhängigkeitsgraphen abgeleitete Attribute. Im Allgemeinen bestätigen die Ergebnisse die Effizienz von Merkmalen, die Abhängigkeitsgraphen entnommen sind, insbesondere Wurzelknoten und n-gram-Pfaden. Experimente, die mit verschiedenen Testmengen diverser Charakteristika durchgeführt wurden, legen nahe, dass auch angenommen werden kann, dass Attribute gefunden werden, die sich auf andere Corpora übertragen lassen. Es gibt zwei weitere Kapitel: zwei und drei. Ersteres untersucht unterschiedliche Strategien, das Netz nach deskriptivem Wissen zu durchforsten. Im Wesentlichen analysiert dieses Kapitel einige Strategien, die darauf abzielen, die Trefferquote (den Recall) deskriptiver Sätze

Reducing Information Variation in Text

International audienc

Reducing Information Variation in Text

International audienc