Non-continuous Syntactic N-grams

Grigori Sidorov

Centro de Investigación en Computación (CIC), Instituto Politécnico Nacional (IPN), Av. Juan de Dios Bátiz, s/n, esq. Othón de Mendizábal, Zacatenco, 07738, México DF, México (e-mail: www.cic.ipn.mx/-sidorov).

Manuscrito recibido 12 de junio de 2013. ]]> Manuscrito aceptado para su publicación 23 de septiembre de 2013.

Resumen

En este artículo presentamos el concepto de los n-gramas sintácticos no-continuos. En nuestros trabajos previos hemos introducido un concepto general de los n-gramas sintácticos, es decir, los n-gramas que se construyen siguiendo las rutas en un árbol sintáctico. Su gran ventaja consiste en que permiten introducir información puramente lingüística (sintáctica) en los métodos computacionales de aprendizaje automático. Su desventaja está relacionada con la necesidad de realizar el análisis sintáctico automático previo. También hemos demostrado que la aplicación de los n-gramas sintácticos en la tarea de atribución de autoría da mejores resultados que el uso de los n-gramas tradicionales. Sin embargo, en dichos trabajos sólo hemos considerado los n-gramas sintácticos continuos, es decir, durante su construcción no se permiten bifurcaciones en las rutas sintácticas. En este artículo, estamos proponiendo a quitar esta limitación, y de esa manera considerar todos los sub-árboles de longitud n de un árbol sintáctico como los n-gramas sintácticos no-continuos. Cabe mencionar que los n-gramas sintácticos continuos son un caso particular de los n-gramas sintácticos no-continuos. El trabajo futuro debe mostrar qué tipo de n-gramas es más útil y para qué tareas de PLN. Se propone la manera formal de escribir un n-grama sintáctico no-continuo usando paréntesis y comas, por ejemplo, "a b [c [d, e], f]". También presentamos en este artículo ejemplos de construcción de n-gramas sintácticos no-continuos para los árboles sintácticos obtenidos usando FreeLing y el parser de Stanford.

Palabras clave: Modelo de espacio vectorial, n-gramas, n-gramas sintácticos continuos, n-gramas sintácticos no-continuos.

Abstract

In this paper, we present the concept of non-continuous syntactic n-grams. In our previous works we introduced the general concept of syntactic n-grams, i.e., n-grams that are constructed by following paths in syntactic trees. Their great advantage is that they allow introducing of the merely linguistic (syntactic) information into machine learning methods. Certain disadvantage is that previous parsing is required. We also proved that their application in the authorship attribution task gives better results than using traditional n-grams. Still, in those works we considered only continuous syntactic n-grams, i.e., the paths in syntactic trees are not allowed to have bifurcations. In this paper, we propose to remove this limitation, so we consider all sub-trees of length « of a syntactic tree as non-continuous syntactic n-grams. Note that continuous syntactic n-grams are the particular case of non-continuous syntactic n-grams. Further research should show which n-grams are more useful and in which NLP tasks. We also propose a formal manner of writing down (representing) non-continuous syntactic n-grams using parenthesis and commas, for example, "a b [c [d, e], f]. In this paper, we also present examples of construction of non-continuous syntactic n-grams on the basis of the syntactic tree of the FreeLing and the Stanford parser.

Key words: Vector space model, n-grams, continuous syntactic n-grams, non-continuous syntactic n-grams.

Agradecimientos

Trabajo realizado con el apoyo de gobierno de la Ciudad de México (proyecto ICYT-DF PICCO10-120), el apoyo parcial del gobierno de México (CONACYT, SNI) e Instituto Politécnico Nacional, México (proyectos SIP 20120418, 20131441,20131702; COFAA), proyecto FP7-PEOPLE-2010-IRSES: Web Information Quality - Evaluation Initiative (WIQ-EI) European Commission project 269180. Agradezco a A. Gelbukh por su ayuda y sugerencias fructíferas.

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