Exploring attributes, sequences, and time in Recommender Systems: From classical to Point-of-Interest recommendation

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Escuela Politécnica Superior, Departamento de Ingenieria Informática. Fecha de lectura: 08-07-2021Since the emergence of the Internet and the spread of digital communications throughout the world, the amount of data stored on the Web has been growing exponentially. In this new digital era, a large number of companies have emerged with the purpose of ltering the information available on the web and provide users with interesting items. The algorithms and models used to recommend these items are called Recommender Systems. These systems are applied to a large number of domains, from music, books, or movies to dating or Point-of-Interest (POI), which is an increasingly popular domain where users receive recommendations of di erent places when they arrive to a city. In this thesis, we focus on exploiting the use of contextual information, especially temporal and sequential data, and apply it in novel ways in both traditional and Point-of-Interest recommendation. We believe that this type of information can be used not only for creating new recommendation models but also for developing new metrics for analyzing the quality of these recommendations. In one of our rst contributions we propose di erent metrics, some of them derived from previously existing frameworks, using this contextual information. Besides, we also propose an intuitive algorithm that is able to provide recommendations to a target user by exploiting the last common interactions with other similar users of the system. At the same time, we conduct a comprehensive review of the algorithms that have been proposed in the area of POI recommendation between 2011 and 2019, identifying the common characteristics and methodologies used. Once this classi cation of the algorithms proposed to date is completed, we design a mechanism to recommend complete routes (not only independent POIs) to users, making use of reranking techniques. In addition, due to the great di culty of making recommendations in the POI domain, we propose the use of data aggregation techniques to use information from di erent cities to generate POI recommendations in a given target city. In the experimental work we present our approaches on di erent datasets belonging to both classical and POI recommendation. The results obtained in these experiments con rm the usefulness of our recommendation proposals, in terms of ranking accuracy and other dimensions like novelty, diversity, and coverage, and the appropriateness of our metrics for analyzing temporal information and biases in the recommendations producedDesde la aparici on de Internet y la difusi on de las redes de comunicaciones en todo el mundo, la cantidad de datos almacenados en la red ha crecido exponencialmente. En esta nueva era digital, han surgido un gran n umero de empresas con el objetivo de ltrar la informaci on disponible en la red y ofrecer a los usuarios art culos interesantes. Los algoritmos y modelos utilizados para recomendar estos art culos reciben el nombre de Sistemas de Recomendaci on. Estos sistemas se aplican a un gran n umero de dominios, desde m usica, libros o pel culas hasta las citas o los Puntos de Inter es (POIs, en ingl es), un dominio cada vez m as popular en el que los usuarios reciben recomendaciones de diferentes lugares cuando llegan a una ciudad. En esta tesis, nos centramos en explotar el uso de la informaci on contextual, especialmente los datos temporales y secuenciales, y aplicarla de forma novedosa tanto en la recomendaci on cl asica como en la recomendaci on de POIs. Creemos que este tipo de informaci on puede utilizarse no s olo para crear nuevos modelos de recomendaci on, sino tambi en para desarrollar nuevas m etricas para analizar la calidad de estas recomendaciones. En una de nuestras primeras contribuciones proponemos diferentes m etricas, algunas derivadas de formulaciones previamente existentes, utilizando esta informaci on contextual. Adem as, proponemos un algoritmo intuitivo que es capaz de proporcionar recomendaciones a un usuario objetivo explotando las ultimas interacciones comunes con otros usuarios similares del sistema. Al mismo tiempo, realizamos una revisi on exhaustiva de los algoritmos que se han propuesto en el a mbito de la recomendaci o n de POIs entre 2011 y 2019, identi cando las caracter sticas comunes y las metodolog as utilizadas. Una vez realizada esta clasi caci on de los algoritmos propuestos hasta la fecha, dise~namos un mecanismo para recomendar rutas completas (no s olo POIs independientes) a los usuarios, haciendo uso de t ecnicas de reranking. Adem as, debido a la gran di cultad de realizar recomendaciones en el ambito de los POIs, proponemos el uso de t ecnicas de agregaci on de datos para utilizar la informaci on de diferentes ciudades y generar recomendaciones de POIs en una determinada ciudad objetivo. En el trabajo experimental presentamos nuestros m etodos en diferentes conjuntos de datos tanto de recomendaci on cl asica como de POIs. Los resultados obtenidos en estos experimentos con rman la utilidad de nuestras propuestas de recomendaci on en t erminos de precisi on de ranking y de otras dimensiones como la novedad, la diversidad y la cobertura, y c omo de apropiadas son nuestras m etricas para analizar la informaci on temporal y los sesgos en las recomendaciones producida

Influence of the processing route on the mechanical properties at high temperatures of Mg-Ni-Y-RE alloys containing LPSO-phases

The mechanical properties at high temperatures of two Mg-Ni-Y-RE alloys prepared by conventional or powder metallurgy routes have been evaluated. All alloys exhibit high-strength up to 250°C but their strength depends more on the composition of the alloy rather than on the processing route. High strength of the alloys arises from their fine grain size but there is an additional contribution of load transfer from the magnesium matrix towards the second phases in the alloys processed by the conventional route while additional hardening in the alloys prepared by powder metallurgy is due to Orowan mechanism. Above 250°C, the strength drops to very low values but all alloys exhibit high elongations and grain boundary sliding is the controlling mechanism. Grain boundary sliding also induces cracking of the coarse second phases into smaller pieces during the initial stages of plastic deformation of conventionally processed alloys

An Approach Toward a Feedback Mechanism for Consensus Reaching Processes Using Gamification to Increase the Experts\u27 Experience

Sometimes, the consensus reaching process in group decision making problems is a challenging task for the people who are in charge of the final choice (usually called experts). Firstly, the consensus is defined as a convergent and iterative process. This implies that it is necessary to keep the experts\u27 attention during the whole process, even if it is longer than expected. Secondly, some of the experts tend to be rigid and they do not change their minds to help in the negotiation process easily. In such a way, we propose a new feedback mechanism that uses some gamification rules, designed as a reward distribution system, in order to transform that task into a game. This change can improve the consensus reaching process in both situations: keeping the experts\u27 attention on the process and motivating those experts that should adjust their preferences

An Approach Toward a Feedback Mechanism for Consensus Reaching Processes Using Gamification to Increase the Experts' Experience

Sometimes, the consensus reaching process in group decision making problems is a challenging task for the people who are in charge of the final choice (usually called experts). Firstly, the consensus is defined as a convergent and iterative process. This implies that it is necessary to keep the experts' attention during the whole process, even if it is longer than expected. Secondly, some of the experts tend to be rigid and they do not change their minds to help in the negotiation process easily. In such a way, we propose a new feedback mechanism that uses some gamification rules, designed as a reward distribution system, in order to transform that task into a game. This change can improve the consensus reaching process in both situations: keeping the experts' attention on the process and motivating those experts that should adjust their preferences

The role of confidence in the evolution of the Spanish economy: empirical evidence from an ARDL model

The aim of this paper is to verify the existence and to determine the nature of long-term relationships between economic agents' confidence, measured by the Economic Sentiment Index (ESI), with some of the "fundamentals" of the Spanish economy. In particular, by modeling this type of relations, we try to determine whether confidence is a dependent (explained) or independent (explanatory) variable. Along with confidence, in our model we incorporate variables such as risk premium of sovereign debt, financial market volatility, unemployment, inflation, public and private debt and the net lending/net borrowing of the economy. For the purpose of obtaining some empirical evidence on the exogenous or endogenous character of the above mentioned variables an ARDL (Autoregressive-Distributed Lag) model is formulated. The model is estimated with quarterly data of the Spanish economy for the period 1990-2012. Our findings suggest that: (a) unemployment is the dependent variable, (b) there is an inverse relationship between ESI in Spain and unemployment; and (c) the Granger causality goes from confidence to unemployment

Guía de buenas prácticas para la gestión de escapes en acuicultura marina. Vol. I. Prevención

Los escapes en acuicultura son un problema que pueden evitarse con la formación del personal que trabaja en las instalaciones en mar abierto. Este libro proporciona los puntos más importantes que tener en cuenta para prevenir los escapes en acuicultura.Cofinanciado por el Fondo Europeo de Pesca y la Fundación Biodiversidad, del Ministerio de Agricultura, Alimentación y Medio Ambiente

Validation of a novel approach to subjective quality evaluation of conventional and 3D broadcasted video services

Transmission errors are the main cause of degradation of the quality of real broadcasted video services. Therefore, knowing their impact on the quality of experience of the end users is a crucial issue. For instance, it would help to improve the performance of the distribution systems, and to develop monitoring tools to automatically estimate the quality perceived by the end users. In this paper we validate a subjective evaluation approach specifically designed to obtain meaningful results of the effects of degradations caused by transmission errors. This methodology has been already used in our previous works with monoscopic and stereoscopic videos. The validation is done by comparing the subjective ratings obtained for typical transmission errors with the proposed methodology and with the standard method Absolute Category Rating. The results show that the proposed approach could provide more representative evaluations of the quality of experience perceived by end users of conventional and 3D broadcasted video services

Subjective study of adaptive streaming strategies for 3DTV

Although the delivery of 3D video services to households is nowadays a reality thanks to frame-compatible formats, many efforts are being made to obtain efficient methods to transmit 3D content offering a high quality of experience to the end users. In this paper, a stereoscopic video streaming scenario is considered and the perceptual impact of various strategies applicable to adaptive streaming situations are compared. Specifically, the mechanisms are based on switching between copies of the content with different coding qualities, on discarding frames of the sequence, on switching from 3D to 2D and on using asymmetric coding of the stereo views. In addition, when video freezes happen, the possibility of keeping the end-to-end latency or maintaining the continuity of the video are considered. These aspects were evaluated carrying out a subjective assessment test considering also visual discomfort issues using a methodology designed to keep as far as possible domestic viewing conditions