| { |
| "paper_id": "E03-1038", |
| "header": { |
| "generated_with": "S2ORC 1.0.0", |
| "date_generated": "2023-01-19T10:24:33.234676Z" |
| }, |
| "title": "Named Entity Recognition for Catalan Using Spanish Resources", |
| "authors": [ |
| { |
| "first": "Xavier", |
| "middle": [], |
| "last": "Carreras", |
| "suffix": "", |
| "affiliation": { |
| "laboratory": "", |
| "institution": "LSI Department Universitat Politecnica de Catalunya Jordi Girona", |
| "location": { |
| "addrLine": "1-3", |
| "postCode": "E-08034", |
| "settlement": "Barcelona" |
| } |
| }, |
| "email": "" |
| }, |
| { |
| "first": "Lluis", |
| "middle": [], |
| "last": "Marquez", |
| "suffix": "", |
| "affiliation": { |
| "laboratory": "", |
| "institution": "LSI Department Universitat Politecnica de Catalunya Jordi Girona", |
| "location": { |
| "addrLine": "1-3", |
| "postCode": "E-08034", |
| "settlement": "Barcelona" |
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| }, |
| "email": "" |
| }, |
| { |
| "first": "Lluis", |
| "middle": [], |
| "last": "Padro", |
| "suffix": "", |
| "affiliation": { |
| "laboratory": "", |
| "institution": "LSI Department Universitat Politecnica de Catalunya Jordi Girona", |
| "location": { |
| "addrLine": "1-3", |
| "postCode": "E-08034", |
| "settlement": "Barcelona" |
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| "abstract": "This work studies Named Entity Recognition (NER) for Catalan without making use of annotated resources of this language. The approach presented is based on machine learning techniques and exploits Spanish resources, either by first training models for Spanish and then translating them into Catalan, or by directly training bilingual models. The resulting models are retrained on unlabelled Catalan data using bootstrapping techniques. Exhaustive experimentation has been conducted on real data, showing competitive results for the obtained NER systems.", |
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| "abstract": [ |
| { |
| "text": "This work studies Named Entity Recognition (NER) for Catalan without making use of annotated resources of this language. The approach presented is based on machine learning techniques and exploits Spanish resources, either by first training models for Spanish and then translating them into Catalan, or by directly training bilingual models. The resulting models are retrained on unlabelled Catalan data using bootstrapping techniques. Exhaustive experimentation has been conducted on real data, showing competitive results for the obtained NER systems.", |
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| "text": "A Named Entity (NE) is a lexical unit consisting of a sequence of contiguous words which refers to a concrete entity -such as a person, a location, an organization or an artifact. Figure 1 contains an example sentence, extracted from the Spanish corpus referred in section 2 and translated into Catalan, including several entities.", |
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| "start": 180, |
| "end": 188, |
| "text": "Figure 1", |
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| "section": "Introduction", |
| "sec_num": "1" |
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| { |
| "text": "There is a wide consensus about that Named Entity Recognition and Classification (NERC) are Natural Language Processing tasks which may improve the performance of many applications, such as Information Extraction, Machine Translation, Question Answering, Topic Detection and Tracking, etc. Thus, interest on detecting and classify-ing those units in a text has kept on growing during the last years.", |
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| "section": "Introduction", |
| "sec_num": "1" |
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| "text": "Named Entity processing consists of two steps, which are usually approached sequentially. First, NEs are detected in the text, and their boundaries delimited (Named Entity Recognition, NER). Second, entities are classified in a predefined set of classes, which usually contain labels such as person, organization, location, etc. (Named Entity Classification, NEC) . In this paper we will focus on the first of these stages, that is, Named Entity boundary detection.", |
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| "start": 292, |
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| "text": "person, organization, location, etc. (Named Entity Classification, NEC)", |
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| "section": "Introduction", |
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| "text": "Previous work in this topic is mainly framed in the Message Understanding Conferences (MUC), devoted to Information Extraction, which included a NERC task. Some MUC systems rely on data-driven approaches, such as Nymble (Bikel et al., 1997) which uses Hidden Markov Models, or ALEMBIC (Aberdeen et al., 1995) , based on Error Driven Transformation Based Learning. Others use only hand-coded knowledge, such as FACILE (Black et al., 1998) which relies on hand written unification context rules with certainty factors, or FASTUS (Appelt et al., 1995) , PLUM (Weischedel, 1995) and NetOwl Extractor (Krupka and Hausman, 1998) which are based on cascaded finite state transducers or pattern matching. There are also hybrid systems combining corpus evidence and gazetteer information (Yu et al., 1998; Borthwick et al., 1998) , or combining hand-written rules with Maximum Entropy models to solve correference (Mikheev et al., 1998) .", |
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| "text": "(Krupka and Hausman, 1998)", |
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| "text": "(Yu et al., 1998;", |
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| "text": "More recent approaches can be found in the proceedings of the shared task at the 2002 edition \"El presidente del [Comite OlImpico Internacional] Learning, CoNLL'02 (Tjong Kim Sang, 2002a) , where several machine-learning systems were compared at the NERC task. Usually, machine learning (ML) systems rely on algorithms that take as input a set of labelled examples for the target task and produce as output a model (which may take different forms, depending on the used algorithm) that can be applied to new examples to obtain a prediction. CoNLL'02 participants used different state-of-the-art ML algorithms, such as Support Vector Machines (McNamee and Mayfield, 2002) , AdaBoost (Can-eras et al., 2002; Tsukamoto et al., 2002) , Transformation-Based methods (Black and Vasilakopoulos, 2002) , Memory-based techniques (Tjong Kim Sang, 2002b) or Hidden Markov Models (Malouf, 2002) , among others.", |
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| "text": "Learning, CoNLL'02 (Tjong Kim Sang, 2002a)", |
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| "section": "Introduction", |
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| "text": "One remarkable aspect of most widely used ML algorithms is that they are supervised, that is, they require a set of labelled data to be trained on. This may cause a severe bottleneck when such data is not available or is expensive to obtain, which is usually the case for minority languages with few pre-existing linguistic resources and/or limited funding possibilities.", |
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| "section": "Introduction", |
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| "text": "Our goal in this paper is to develop a low-cost Named Entity recognition system for Catalan. To achieve this, we take advantage of the facts that Spanish and Catalan are two Romance languages with similar syntactic structure, and that -since Spanish and Catalan social and cultural environments greatly overlap-many Named Entities appear in both languages corpora. Relying on this structural and content similarity, we will build our Catalan NE recognizer on the following assumptions: (a) Named Entities appear in the same contexts in both languages, and (b) Named Entities are composed by similar patterns in both languages.", |
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| "section": "Introduction", |
| "sec_num": "1" |
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| "text": "The work departs from the use of existing annotated Spanish corpora and machine learning tech-niques to obtain Spanish NER models. We first build low-cost resources (about 10 person-hours each), namely a small Catalan training corpus and translation dictionaries from Spanish to Catalan. We then present and evaluate several strategies to obtain a low-cost Catalan system. Simple naive strategies consist of learning from the large Spanish corpus a model which makes no use of lexical information, or learning a model for Catalan using the small Catalan corpus. More sophisticated strategies are translating a Spanish model into Catalan, or directly learning a bilingual model applicable to both languages. Experimentation shows that the latter strategies, specially the bilingual models, provide very good performance, somewhat better than the former techniques. We also study the evolution of these models within a bootstrapping process, observing no significant improvement.", |
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| "section": "Introduction", |
| "sec_num": "1" |
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| "text": "Next section of the paper describes the used corpora and evaluation measures. Section 3 describes the NER learning system. Section 4 presents the strategies to obtain a low-cost Catalan NER system and provides results. Bootstrapping is studied in section 5, and, finally, section 6 concludes.", |
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| "section": "Introduction", |
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| "text": "The experimentation of this work has been carried on two corpora, one for each language. In both cases, the corpora consist of sentences extracted from news articles of same year, namely year 2,000. The Spanish data corresponds to the CoNLL 2002 Shared Task Spanish data, the original source being the EFE Spanish Newswire Agency. It consists of three files: a training set, a development set and a test set. The first two are used respectively to train and tune a system, and the latter is used to evaluate and compare systems. From this corpus, we selected two sets for manual annotation: a training set, to train a system, and a test set, to perform the evaluation. The remaining data was left as unlabelled data.", |
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| "section": "Data and Evaluation", |
| "sec_num": "2" |
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| "text": "As evaluation method we use the common measures for recognition tasks: precision, recall and F1 . Precision is the percentage of NEs predicted by a system which are correct. Recall is the percentage of NEs in the data that a system correctly recognizes. Finally, the F1 measure computes the harmonic mean of precision (p) and recall (r) as 2 p \u2022 Op + r).", |
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| "section": "Data and Evaluation", |
| "sec_num": "2" |
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| "text": "The Spanish NER system is based on the best system at CoNLL'02, which makes use of a set of AdaBoost-based binary classifiers for recognizing the Named Entities in running text. See (Carreras et al., 2002) for details.", |
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| "section": "The Spanish NER System", |
| "sec_num": "3" |
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| "text": "The NE recognition task is performed as a sequence tagging problem through the well-known BIO labelling scheme. Here, the input sentence is treated as a word sequence and the output tagging codifies the NEs in the sentence. In particular, each word is tagged as either the beginning of a NE (B tag), a word inside a NE (I tag), or a word outside a NE (0 tag). In our case, a NER model is composed by: (a) a representation function, which maps a word and its context into a set of features, and (b) three binary classifiers (one corresponding to each tag) which, operating on the features, are used for tagging each word. When tagging, a sentence is processed from left to right, selecting for each word the tag with maximum confidence that is coherent with the current solution (I-tag sequences must be preceded by a B-tag). When learning a model, all the words in the training set are used as training examples, applying a one-vsall binarization of the 3-class classification problem.", |
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| "section": "The Spanish NER System", |
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| "text": "The representation consists in a shifting window anchored in a word w, which encodes the local context of w with which a classifier will operate. In the window, each word around w is codified with a set of primitive features, together with its relative position to w. Each primitive feature with each relative position and each possible value forms a final binary feature for the classifier (e.g., \"the word_form at position -2 is calle\"). Particularly, the set of primitive features applied to each word in the window is the following:", |
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| "section": "The Spanish NER System", |
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| }, |
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| "text": "\u2022 Lexical Features The word forms.", |
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| "section": "The Spanish NER System", |
| "sec_num": "3" |
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| "text": "\u2022 Orthographic Features These are binary and not mutually exclusive features that test whether the following predicates hold in the word: initial-caps, all-caps, contains-digits, all-digits, alphanumeric, roman-number, contains-dots, contains-hyphen, acronym, lonely-initial, punctuation-mark, singlechar, functional-word , and URL. Functional words are determiners and prepositions which typically appear inside NEs.", |
| "cite_spans": [ |
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| "text": "all-caps, contains-digits, all-digits, alphanumeric, roman-number, contains-dots, contains-hyphen, acronym, lonely-initial, punctuation-mark, singlechar, functional-word", |
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| "section": "The Spanish NER System", |
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| "text": "\u2022 Affixes Test whether a word beginning (or ending) matches with a common NE prefix (or suffix). The list of affixes has been automatically extracted from the Spanish training set, by taking those NE affixes of up to 4 symbols which occur more than 100 times.", |
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| "section": "The Spanish NER System", |
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| "text": "\u2022 Word Type Patterns The type of a word is either functional, capitalized, lowercased, punctuation mark, quote or other. Each conjunction of types of contiguous words is a word type pattern, but only patterns in the window which include the anchoring word are considered.", |
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| "section": "The Spanish NER System", |
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| "text": "\u2022 Left Predictions The tags being predicted in the current classification. These features only apply to the words in the window to the left of the anchoring word w.", |
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| "section": "The Spanish NER System", |
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| "text": "As learning algorithm we use the binary AdaBoost with confidence rated predictions. The idea of this algorithm is to learn an accurate strong classifier by linearly combining, in a weighted voting scheme, many simple and moderatelyaccurate base classifiers or rules. Each base rule is learned sequentially by presenting the base learning algorithm a weighting over the examples, which is dynamically adjusted depending on the behavior of the previously learned rules. We refer the reader to (Schapire and Singer, 1999) for details about the general algorithm, and to (Schapire, 2002) for successful applications to many areas, including several NLP tasks.", |
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| "text": "(Schapire and Singer, 1999)", |
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| "section": "The Spanish NER System", |
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| "text": "In our setting, the boosting algorithm combines several small fixed-depth decision trees. Each branch of a tree is, in fact, a conjunction of binary features, allowing the strong boosting classifier to work with complex and expressive rules.", |
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| "section": "The Spanish NER System", |
| "sec_num": "3" |
| }, |
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| "text": "In this section we study the portability of a NER system from Spanish to Catalan. Our approach is to port a NER system by porting the model features from Spanish to Catalan. In particular, we concentrate on the features which are language dependent, namely, the lexical features (or word forms) and the functional words. All other features are left unchanged.", |
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| "section": "Porting to Catalan", |
| "sec_num": "4" |
| }, |
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| "text": "Two alternative translation dictionaries from Spanish to Catalan and vice-versa have been built for the task. They contain a one to one correspondence between Spanish and Catalan words. For instance, an entry in a dictionary is \"calle caner\", meaning that the Spanish word \"calle\" (\"street\" in English) corresponds to the Catalan word \"caner\".", |
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| "section": "Porting to Catalan", |
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| "text": "In order to obtain the relevant vocabulary for NER, we have run several trainings of the Spanish NER system by varying the system parameters, and we have extracted from the learned models all the involved Spanish lexical features. These Spanish words form a set of 5,024 entries.", |
| "cite_spans": [], |
| "ref_spans": [], |
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| "section": "Porting to Catalan", |
| "sec_num": "4" |
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| "text": "The first dictionary has been manually completed, with an estimated cost of about 10 person hours of a bilingual speaker (7.2 sec/word). Note that translations are made with no context information, and with no linguistic criteria. The translator's common sense is blindly assumed to select the best choice among all possible translations.", |
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| "section": "Porting to Catalan", |
| "sec_num": "4" |
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| "text": "The second dictionary has been automatically completed using the InterNOSTRUM Spanish-Catalan machine translation system developed by the Software Department of the University of Alacane . In this case, the translations have also been resolved without any context information, and the entries not recognized by InterNOSTRUM (about 17%) have been left unchanged.", |
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| "section": "Porting to Catalan", |
| "sec_num": "4" |
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| "text": "Our first approach to obtain a NER model for Catalan consists in first learning a NER model for Spanish using Spanish annotated data, and then translating its lexical features from Spanish into Catalan using the translation dictionary. In our particular case, a NER model is composed by the B, I and 0 classifiers, each of which is a combination of a number of base decision trees. The model translation, therefore, consists in translating every decision tree by translating those nodes in the tree which evaluate lexical features. For instance, considering the translation \"calle caner\", a node for Spanish with feature \"word:-2:calle\", testing whether the word form at relative position -2 is \"calle\", will be translated into the node for Catalan \"word:-2:carrer\", which will test whether the -2 word is \"caner\".", |
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| "eq_spans": [], |
| "section": "Model Translation", |
| "sec_num": "4.1" |
| }, |
| { |
| "text": "As a result, we obtain models which are trained on Spanish and applied to Catalan text.", |
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| "section": "Model Translation", |
| "sec_num": "4.1" |
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| "text": "As a more sophisticated alternative, we propose a bilingual model which works for Spanish and Catalan at the same time. We do this by using what we call cross-linguistic features, instead of the monolingual word forms specified above. Assume a feature lang which takes value es or ca, depending on the language under consideration. A cross-linguistic feature is just a binary feature corresponding to an entry in the translation dictionary, \"es_w ca_w\", which is satisfied as follows: ", |
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| "section": "Cross-Linguistic Features", |
| "sec_num": "4.2" |
| }, |
| { |
| "text": "This representation allows to learn from a corpus consisting of mixed Spanish and Catalan examples. The idea here is to take advantage of the fact that the concept of NE is mostly shared by both languages, but differs in the lexical information, which we exploit through the lexical translations. With this we can learn a bilingual model which is able to recognize NEs both for Spanish and Catalan, but that may be trained with fewor even any-data of one language, in our case Catalan.", |
| "cite_spans": [], |
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| "eq_spans": [], |
| "section": "X-Ling es_wr,ca_w(W)", |
| "sec_num": null |
| }, |
| { |
| "text": "A third approach is the usual learning of a NER system using training data of the same language. Since our interest relies on developing a low-cost NER system for Catalan, we have performed standard learning on a small training set (described in table 1), with an annotation cost comparable to the cost of building the translation dictionary (about 10 person hours).", |
| "cite_spans": [], |
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| "section": "Direct Learning in Catalan", |
| "sec_num": "4.3" |
| }, |
| { |
| "text": "Preliminary tuning on Spanish was performed on the Spanish development set, in order to fix learning parameters. The window sizes were set to 3 words around, except for the orthographic window, with size of 1 word around. Concerning classifiers, the depth of the base decision trees was fixed to 4 levels (i.e., tree branches represent conjunctions of up to 4 basic features). When applicable, the number of decision trees per classifier was automatically tuned in the Spanish development set selecting, from up to 2,000 base trees, the number which maximizes the F1 measure. Otherwise it was fixed to 800.", |
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| "section": "Results", |
| "sec_num": "4.4" |
| }, |
| { |
| "text": "First, in order to have a baseline for the data sets, two basic models were learned. The first, NO_LEX, makes no use of lexical information at all, that is, focuses only on orthographic features, affixes, type patterns and left predictions. We trained this model on the Spanish training data and we directly applied it to both languages. As a second baseline, a model for Catalan (including lexical information) LEx.ca, was trained using the small Catalan training set.", |
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| "section": "Results", |
| "sec_num": "4.4" |
| }, |
| { |
| "text": "Following the approach described in Section 4.1, a model was learned on the Spanish training set, and then translated into Catalan, generating the model LEx.es2ca. Note that this model is also applicable both to Spanish and Catalan, considering, respectively, the learned set of Spanish lexical forms or the translated Catalan ones. In addition, we tested the influence of cross-linguistic features presented in Section 4.2. We trained one model, X-LING\", only with the Spanish training data, and a second model, X-LING mix , using both the Spanish training data and the Catalan training set. In both approaches the experiments were replicated using the two available translation dictionaries. Table 2 presents the results of all the learned models on the test sets. Clearly, comparing the performance of the NO_LEX model versus the others, it can be stated that lexical information significantly helps on the NER task on both languages.", |
| "cite_spans": [], |
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| "text": "Looking at the results on the Catalan test (right block), all the models using the manual dictionary achieve a very competitive performance over 90% of F1 measure. Therefore, the techniques to adapt a NER model to Catalan seem to work considerably well. The LEx.ca model performs somewhat worse (89.18%) than others (probably because of the reduced size of the training set), indicating that, in similar conditions of annotation effort, it is preferable to translate the models than to learn from the small Catalan corpus.", |
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| "text": "The LEx.es2ca and X-LING\" models perform nearly the same. Actually, since they are trained on the same Spanish data, the models are fairly equivalent, and the minor differences may be attributed to the fixed vocabulary of the crosslinguistic model. Besides, the X-LINGInix model, trained with mixed corpora, achieves the best results (91.18%), which supports our arguments on learning simultaneously from both languages.", |
| "cite_spans": [], |
| "ref_spans": [], |
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| { |
| "text": "Another positive result shown in table 2 is that the X-LING models using the automatically generated dictionary perform almost as well as using the manual dictionary (a loss of about 0.5 points in F1 is observed in both cases). After a manual inspection, we explain the bad results of LEx.es2ca with the automatic dictionary (87.53% compared to 90.55%) by the large number of errors coming from the translation of Spanish words, which are directly applied on the Catalan data. Table 2 : Evaluation of the learned models on the test datasets for Spanish (es) and Catalan (ca). The \"es\" and \"ca train\" columns indicate the training material used in each model. The \"dim\" column specifies the dicctionary (either manual or automatic) used for translating models. The NO_LEX model learns without making use of lexical information. The LEx.ca model is a baseline standard model developed on Catalan. The LEx.es2ca is a translated model from Spanish to Catalan. The X-LING models are bilingual models using cross-linguistic features.", |
| "cite_spans": [], |
| "ref_spans": [ |
| { |
| "start": 477, |
| "end": 484, |
| "text": "Table 2", |
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| } |
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| "eq_spans": [], |
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| "sec_num": "4.4" |
| }, |
| { |
| "text": "are capable of discarding useless erroneous crosslinguistic features.", |
| "cite_spans": [], |
| "ref_spans": [], |
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| "sec_num": "4.4" |
| }, |
| { |
| "text": "Regarding the performance on Spanish (left block), the original model, LEx.es2ca, working with Spanish lexical information, obtains the best results (92.85%), but cross-linguistic models are still competitive (with a small loss of 0.4 points in F1 ). This fact indicates that training with both languages at the same time does not significantly hurt the performance of the individual Spanish model. Additionally, the multilingual models are simpler to use, since they work straightforwardly with both languages, whereas form-based translated models are specific for each language.", |
| "cite_spans": [], |
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| "sec_num": "4.4" |
| }, |
| { |
| "text": "We would like to note also that the systems achieve the same order of performance for both languages, which was shown to be very competitive in CoNLL' 02. Although the table figures correspond to evaluations in different sets, and thus, can not be directly compared, the two corpora are similar, since both consist of news article from the same dates and geographical area.", |
| "cite_spans": [], |
| "ref_spans": [], |
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| "sec_num": "4.4" |
| }, |
| { |
| "text": "As far as the cost concerns, it happens that the better the performance of a model, the more the resources needed to obtain it. Probably, the best tradeoff is observed in the case of X-LINGmix with the automatic dictionary, which allows to almost automatically construct an accurate NER system for Catalan (90.71%) at the only cost of 10 person hours of corpus annotation.", |
| "cite_spans": [], |
| "ref_spans": [], |
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| "sec_num": "4.4" |
| }, |
| { |
| "text": "This section describes an attempt to improve the NER models via bootstrapping techniques, that is, making use of the available large amount of unlabelled data in Catalan.", |
| "cite_spans": [], |
| "ref_spans": [], |
| "eq_spans": [], |
| "section": "Bootstrapping the models", |
| "sec_num": "5" |
| }, |
| { |
| "text": "We describe a simple, naive strategy for the bootstrapping process. The unlabelled data in Catalan has been randomly divided into a number of equal-sized disjoint subsets Si .. . SN, containing 1,000 sentences each. Given an initial NER model Mo and a base labelled data set TL, the process is as follows:", |
| "cite_spans": [], |
| "ref_spans": [], |
| "eq_spans": [], |
| "section": "Bootstrapping the models", |
| "sec_num": "5" |
| }, |
| { |
| "text": "1. For i = 1 N do : (a) Identify the Named Entities in Si ... using model (b) Learn a new model Mi using as training data TL U Vi=1 S.", |
| "cite_spans": [], |
| "ref_spans": [], |
| "eq_spans": [], |
| "section": "Bootstrapping the models", |
| "sec_num": "5" |
| }, |
| { |
| "text": "At each iteration, a new unlabelled fold is included in the learning process. First, the folds are labelled by the current model, and then, a new model is learned using the base training data plus the label-predicted folds.", |
| "cite_spans": [], |
| "ref_spans": [], |
| "eq_spans": [], |
| "section": "Output Model MN.", |
| "sec_num": "2." |
| }, |
| { |
| "text": "We have run the process for three of the models above, always using the manual dictionary: LEX.ca , with Catalan training set as TL; X-LINGes, with Spanish training set as TL; and X-LINGmix , with Tr, as the union of the Spanish and Catalan training material. Since the LEx.es2ca model can not mix its initial Spanish training with the Catalan folds, we have avoided the model in the experiment. Figure 2 depicts the evolution of the F 1 measure through the bootstrapping process, for 7 iterations. The model LEx.ca experiments a sharp drop of 2 points in the first iteration, and beyond iteration 5 gets stable at 87.41%. In our opinion, the Catalan training set is not big enough and the errors in the retraining folds degrade the performance of the bootstrapped model. On the other hand, the crosslinguistic models show a slightly better behavior, achieving a maximum increase of about 0.5 points, getting also somewhat stable beyond iteration 5. Again, X-LINGnaix is slightly better than X-LING\". Bootstrapping, therefore, is not very helpful on improving models. However, these models seem to have learned a robust concept which overcomes the errors produced when relabelling folds. It is also interesting to realize that the inclusion of the Catalan training is crucial in the difference in performance between the cross-linguistic models: the X-LING\" model is not able to acquire from the unlabelled data the same behavior than the X-LINGmix model, which has access to the manually annotated Catalan set (nearly of the same size than each fold).", |
| "cite_spans": [], |
| "ref_spans": [ |
| { |
| "start": 396, |
| "end": 404, |
| "text": "Figure 2", |
| "ref_id": "FIGREF1" |
| } |
| ], |
| "eq_spans": [], |
| "section": "Output Model MN.", |
| "sec_num": "2." |
| }, |
| { |
| "text": "More complex variations to the above bootstrapping strategy have been experimented. Basically, our direction has concentrated on select-ing from the unlabelled material only the \"good\" sentences for the learning process, by taking those which maximize a mean of the confidences of the predictions on a sentence, or those in which two different models agree on the prediction. In all cases, results lead to conclusions similar to the ones described above.", |
| "cite_spans": [], |
| "ref_spans": [], |
| "eq_spans": [], |
| "section": "Output Model MN.", |
| "sec_num": "2." |
| }, |
| { |
| "text": "We have presented an experimental work on developing low-cost Named Entity recognizers for a language with no available annotated resources, using as a starting point existing resources for a similar language. We have devised and evaluated several strategies to build a Catalan NER system using only annotated Spanish data and unlabelled Catalan text, and compared our approach with a classical bootstrapping setting where a small initial corpus in the target language is hand tagged.", |
| "cite_spans": [], |
| "ref_spans": [], |
| "eq_spans": [], |
| "section": "Conclusions and Further Work", |
| "sec_num": "6" |
| }, |
| { |
| "text": "The main conclusions drawn form the presented results are: 1) At same cost, the hand translation of a Spanish model is better than hand annotating a small Catalan training corpus from which directly learn a model. 2) The translation of the Spanish model can be automatically done by using a Spanish-Catalan machine translation system, obtaining also very competitive results. 3) The best strategy turned out to be the use of cross-linguistic features, which enables the training of models using mixed corpora, and results in a system able to work reasonably on both languages.", |
| "cite_spans": [], |
| "ref_spans": [], |
| "eq_spans": [], |
| "section": "Conclusions and Further Work", |
| "sec_num": "6" |
| }, |
| { |
| "text": "Results of the experiments with a simple bootstrapping strategy suggest several conclusions. First, LEx.ca is not improved via bootstrapping, probably due to the small size of the Catalan training corpus. Second, bootstrapping slightly improves initial X-LING models, producing robust models which are not degraded by the noise introduced in subsequent iterations of bootstrapping.", |
| "cite_spans": [], |
| "ref_spans": [], |
| "eq_spans": [], |
| "section": "Conclusions and Further Work", |
| "sec_num": "6" |
| }, |
| { |
| "text": "Some open issues that should be addressed in the future include an improvement of the quality and coverage of the automatic translation of dictionary entries, and a further development of the idea of cross-linguistic features, extending it either from bilingual to multilingual translations, or including semantic relations, through the use of WordNet or similar ontologies. This could open the door to apply the method to groups of similar languages (e.g., between Romance languages like Catalan, French, Galician, Italian, Spanish, etc.).", |
| "cite_spans": [], |
| "ref_spans": [], |
| "eq_spans": [], |
| "section": "Conclusions and Further Work", |
| "sec_num": "6" |
| }, |
| { |
| "text": "In addition, bootstrapping techniques should be better studied in this domain, in order to take advantage of the large quantities of available unlabelled data. Particularly, we think that it is worth investigating the size and selection of the retraining corpora, and the combination of several algorithms or example views like in the co-training algorithms presented in (Collins and Singer, 1999; Abney, 2002) .", |
| "cite_spans": [ |
| { |
| "start": 371, |
| "end": 397, |
| "text": "(Collins and Singer, 1999;", |
| "ref_id": "BIBREF9" |
| }, |
| { |
| "start": 398, |
| "end": 410, |
| "text": "Abney, 2002)", |
| "ref_id": "BIBREF1" |
| } |
| ], |
| "ref_spans": [], |
| "eq_spans": [], |
| "section": "Conclusions and Further Work", |
| "sec_num": "6" |
| } |
| ], |
| "back_matter": [ |
| { |
| "text": "The authors thank the anonymous reviewers for their valuable comments and suggestions in order to prepare the final version of this paper.This research has been partially funded by the Spanish Research Department (HERMES T1C2000-0335-0O3-02, PETRA T1C2000-1735-CO2-02), by the European Comission (MEAN-ING IST-2001-34460), and by the Catalan Research Department (CIRIT's consolidated research group 2001SGR-00254 and research grant 2001FI-00663).", |
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| "section": "Acnowledgements", |
| "sec_num": null |
| } |
| ], |
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| "type_str": "figure", |
| "text": "system is freely available at the following URL: http://www.internostrum.com ." |
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| "content": "<table><tr><td>Figure 1: Example of a Spanish (top) and Catalan (bottom) sentence including several Named Entities</td></tr><tr><td>between brackets (PER=person, Loc=location, oRG=organization).</td></tr></table>", |
| "text": "oRG, [Jose Antonio Samaranch]pER, se reuni6 el lunes en [Nueva Yorkkoc eon investigadores del [FBI]oRG y del [Departamento de JusticialoRG:\" \"El president del [Comite Olimpie Internacional]oRG, [Josep Antoni Samaranch]pER, es va reunir dilluns a [Nova York]Loc amb investigadors del [FBI]oRG i del [Departament de Justicia]oRG.\"", |
| "num": null |
| }, |
| "TABREF1": { |
| "type_str": "table", |
| "html": null, |
| "content": "<table><tr><td>shows the number of sentences, words and</td></tr><tr><td>Named Entities in each set. For Catalan, we had</td></tr></table>", |
| "text": "", |
| "num": null |
| } |
| } |
| } |
| } |
