Enhancing Privacy and Fairness in Search Systems

Following a period of expedited progress in the capabilities of digital systems, the society begins to realize that systems designed to assist people in various tasks can also harm individuals and society. Mediating access to information and explicitly or implicitly ranking people in increasingly many applications, search systems have a substantial potential to contribute to such unwanted outcomes. Since they collect vast amounts of data about both searchers and search subjects, they have the potential to violate the privacy of both of these groups of users. Moreover, in applications where rankings influence people's economic livelihood outside of the platform, such as sharing economy or hiring support websites, search engines have an immense economic power over their users in that they control user exposure in ranked results. This thesis develops new models and methods broadly covering different aspects of privacy and fairness in search systems for both searchers and search subjects. Specifically, it makes the following contributions: (1) We propose a model for computing individually fair rankings where search subjects get exposure proportional to their relevance. The exposure is amortized over time using constrained optimization to overcome searcher attention biases while preserving ranking utility. (2) We propose a model for computing sensitive search exposure where each subject gets to know the sensitive queries that lead to her profile in the top-k search results. The problem of finding exposing queries is technically modeled as reverse nearest neighbor search, followed by a weekly-supervised learning to rank model ordering the queries by privacy-sensitivity. (3) We propose a model for quantifying privacy risks from textual data in online communities. The method builds on a topic model where each topic is annotated by a crowdsourced sensitivity score, and privacy risks are associated with a user's relevance to sensitive topics. We propose relevance measures capturing different dimensions of user interest in a topic and show how they correlate with human risk perceptions. (4) We propose a model for privacy-preserving personalized search where search queries of different users are split and merged into synthetic profiles. The model mediates the privacy-utility trade-off by keeping semantically coherent fragments of search histories within individual profiles, while trying to minimize the similarity of any of the synthetic profiles to the original user profiles. The models are evaluated using information retrieval techniques and user studies over a variety of datasets, ranging from query logs, through social media and community question answering postings, to item listings from sharing economy platforms.Nach einer Zeit schneller Fortschritte in den Fähigkeiten digitaler Systeme beginnt die Gesellschaft zu erkennen, dass Systeme, die Menschen bei verschiedenen Aufgaben unterstützen sollen, den Einzelnen und die Gesellschaft auch schädigen können. Suchsysteme haben ein erhebliches Potenzial, um zu solchen unerwünschten Ergebnissen beizutragen, weil sie den Zugang zu Informationen vermitteln und explizit oder implizit Menschen in immer mehr Anwendungen in Ranglisten anordnen. Da sie riesige Datenmengen sowohl über Suchende als auch über Gesuchte sammeln, können sie die Privatsphäre dieser beiden Benutzergruppen verletzen. In Anwendungen, in denen Ranglisten einen Einfluss auf den finanziellen Lebensunterhalt der Menschen außerhalb der Plattform haben, z. B. auf Sharing-Economy-Plattformen oder Jobbörsen, haben Suchmaschinen eine immense wirtschaftliche Macht über ihre Nutzer, indem sie die Sichtbarkeit von Personen in Suchergebnissen kontrollieren. In dieser Dissertation werden neue Modelle und Methoden entwickelt, die verschiedene Aspekte der Privatsphäre und der Fairness in Suchsystemen, sowohl für Suchende als auch für Gesuchte, abdecken. Insbesondere leistet die Arbeit folgende Beiträge: (1) Wir schlagen ein Modell für die Berechnung von fairen Rankings vor, bei denen Suchsubjekte entsprechend ihrer Relevanz angezeigt werden. Die Sichtbarkeit wird im Laufe der Zeit durch ein Optimierungsmodell adjustiert, um die Verzerrungen der Sichtbarkeit für Sucher zu kompensieren, während die Nützlichkeit des Rankings beibehalten bleibt. (2) Wir schlagen ein Modell für die Bestimmung kritischer Suchanfragen vor, in dem für jeden Nutzer Aanfragen, die zu seinem Nutzerprofil in den Top-k-Suchergebnissen führen, herausgefunden werden. Das Problem der Berechnung von exponierenden Suchanfragen wird als Reverse-Nearest-Neighbor-Suche modelliert. Solche kritischen Suchanfragen werden dann von einem Learning-to-Rank-Modell geordnet, um die sensitiven Suchanfragen herauszufinden. (3) Wir schlagen ein Modell zur Quantifizierung von Risiken für die Privatsphäre aus Textdaten in Online Communities vor. Die Methode baut auf einem Themenmodell auf, bei dem jedes Thema durch einen Crowdsourcing-Sensitivitätswert annotiert wird. Die Risiko-Scores sind mit der Relevanz eines Benutzers mit kritischen Themen verbunden. Wir schlagen Relevanzmaße vor, die unterschiedliche Dimensionen des Benutzerinteresses an einem Thema erfassen, und wir zeigen, wie diese Maße mit der Risikowahrnehmung von Menschen korrelieren. (4) Wir schlagen ein Modell für personalisierte Suche vor, in dem die Privatsphäre geschützt wird. In dem Modell werden Suchanfragen von Nutzer partitioniert und in synthetische Profile eingefügt. Das Modell erreicht einen guten Kompromiss zwischen der Suchsystemnützlichkeit und der Privatsphäre, indem semantisch kohärente Fragmente der Suchhistorie innerhalb einzelner Profile beibehalten werden, wobei gleichzeitig angestrebt wird, die Ähnlichkeit der synthetischen Profile mit den ursprünglichen Nutzerprofilen zu minimieren. Die Modelle werden mithilfe von Informationssuchtechniken und Nutzerstudien ausgewertet. Wir benutzen eine Vielzahl von Datensätzen, die von Abfrageprotokollen über soziale Medien Postings und die Fragen vom Q&A Forums bis hin zu Artikellistungen von Sharing-Economy-Plattformen reichen

Terms interrelationship query expansion to improve accuracy of Quran search

Quran retrieval system is becoming an instrument for users to search for needed information. The search engine is one of the most popular search engines that successfully implemented for searching relevant verses queries. However, a major challenge to the Quran search engine is word ambiguities, specifically lexical ambiguities. With the advent of query expansion techniques for Quran retrieval systems, the performance of the Quran retrieval system has problem and issue in terms of retrieving users needed information. The results of the current semantic techniques still lack precision values without considering several semantic dictionaries. Therefore, this study proposes a stemmed terms interrelationship query expansion approach to improve Quran search results. More specifically, related terms were collected from different semantic dictionaries and then utilize to get roots of words using a stemming algorithm. To assess the performance of the stemmed terms interrelationship query expansion, experiments were conducted using eight Quran datasets from the Tanzil website. Overall, the results indicate that the stemmed terms interrelationship query expansion is superior to unstemmed terms interrelationship query expansion in Mean Average Precision with Yusuf Ali 68%, Sarawar 67%, Arberry 72%, Malay 65%, Hausa 62%, Urdu 62%, Modern Arabic 60% and Classical Arabic 59%

Research Paper: Process Mining and Synthetic Health Data: Reflections and Lessons Learnt

Analysing the treatment pathways in real-world health data can provide valuable insight for clinicians and decision-makers. However, the procedures for acquiring real-world data for research can be restrictive, time-consuming and risks disclosing identifiable information. Synthetic data might enable representative analysis without direct access to sensitive data. In the first part of our paper, we propose an approach for grading synthetic data for process analysis based on its fidelity to relationships found in real-world data. In the second part, we apply our grading approach by assessing cancer patient pathways in a synthetic healthcare dataset (The Simulacrum provided by the English National Cancer Registration and Analysis Service) using process mining. Visualisations of the patient pathways within the synthetic data appear plausible, showing relationships between events confirmed in the underlying non-synthetic data. Data quality issues are also present within the synthetic data which reflect real-world problems and artefacts from the synthetic dataset’s creation. Process mining of synthetic data in healthcare is an emerging field with novel challenges. We conclude that researchers should be aware of the risks when extrapolating results produced from research on synthetic data to real-world scenarios and assess findings with analysts who are able to view the underlying data

Measuring the impact of COVID-19 on hospital care pathways

Care pathways in hospitals around the world reported significant disruption during the recent COVID-19 pandemic but measuring the actual impact is more problematic. Process mining can be useful for hospital management to measure the conformance of real-life care to what might be considered normal operations. In this study, we aim to demonstrate that process mining can be used to investigate process changes associated with complex disruptive events. We studied perturbations to accident and emergency (A &E) and maternity pathways in a UK public hospital during the COVID-19 pandemic. Co-incidentally the hospital had implemented a Command Centre approach for patient-flow management affording an opportunity to study both the planned improvement and the disruption due to the pandemic. Our study proposes and demonstrates a method for measuring and investigating the impact of such planned and unplanned disruptions affecting hospital care pathways. We found that during the pandemic, both A &E and maternity pathways had measurable reductions in the mean length of stay and a measurable drop in the percentage of pathways conforming to normative models. There were no distinctive patterns of monthly mean values of length of stay nor conformance throughout the phases of the installation of the hospital’s new Command Centre approach. Due to a deficit in the available A &E data, the findings for A &E pathways could not be interpreted

Towards Scalable Personalization

The ever-growing amount of online information calls for Personalization. Among the various personalization systems, recommenders have become increasingly popular in recent years. Recommenders typically use collaborative filtering to suggest the most relevant items to their users. The most prominent challenges underlying personalization are: scalability, privacy, and heterogeneity. Scalability is challenging given the growing rate of the Internet and its dynamics, both in terms of churn (i.e., users might leave/join at any time) and changes of user interests over time. Privacy is also a major concern as users might be reluctant to expose their profiles to unknown parties (e.g., other curious users), unless they have an incentive to significantly improve their navigation experience and sufficient guarantees about their privacy. Heterogeneity poses a major technical difficulty because, to be really meaningful, the profiles of users should be extracted from a number of their navigation activities (heterogeneity of source domains) and represented in a form that is general enough to be leveraged in the context of other applications (heterogeneity of target domains). In this dissertation, we address the above-mentioned challenges. For scalability, we introduce democratization and incrementality. Our democratization approach focuses on iteratively offloading the computationally expensive tasks to the user devices (via browsers or applications). This approach achieves scalability by employing the devices of the users as additional resources and hence the throughput of the approach (i.e., number of updates per unit time) scales with the number of users. Our incrementality approach deals with incremental similarity metrics employing either explicit (e.g., ratings) or implicit (e.g., consumption sequences for users) feedback. This approach achieves scalability by reducing the time complexity of each update, and thereby enabling higher throughput. We tackle the privacy concerns from two perspectives, i.e., anonymity from either other curious users (user-level privacy) or the service provider (system-level privacy). We strengthen the notion of differential privacy in the context of recommenders by introducing distance-based differential privacy (D2P) which prevents curious users from even guessing any category (e.g., genre) in which a user might be interested in. We also briefly introduce a recommender (X-REC) which employs uniform user sampling technique to achieve user-level privacy and an efficient homomorphic encryption scheme (X-HE) to achieve system-level privacy. We also present a heterogeneous recommender (X-MAP) which employs a novel similarity metric (X-SIM) based on paths across heterogeneous items (i.e., items from different domains). To achieve a general form for any user profile, we generate her AlterEgo profile in a target domain by employing an item-to-item mapping from a source domain (e.g., movies) to a target domain (e.g., books). Moreover, X-MAP also enables differentially private AlterEgos. While X-MAP employs user-item interactions (e.g., ratings), we also explore the possibility of heterogeneous recommendation by using content-based features of users (e.g., demography, time-varying preferences) or items (e.g., popularity, price)

The Songs of Our Past

Advancements in technology have resulted in unique changes in the way people interact with music today: Small, portable devices allow listening to it everywhere and provide access to thousands or, via streaming, even millions of songs. In addition, all played tracks can be logged with an accuracy down to the second. So far, these music listening histories are mostly used for music recommendation and hidden from their actual creators. But people may also benefit from this data more directly: as memory extensions that allow retrieving the name of a title, for rediscovering old favorites and reflecting about their lives. Additionally, listening histories can be representations of the implicit relationships between musical items. In this thesis, I discuss the contents of these listening histories and present software tools that give their owners the chance to work with them. As a first approach to understanding the patterns contained in listening histories I give an overview of the relevant literature from musicology, human-computer-interaction and music information retrieval. This literature review identifies the context as a main influence for listening: from the musical and temporal to the demographical and social. I then discuss music listening histories as digital memory extensions and a part of lifelogging data. Based on this notion, I present what an ideal listening history would look like and how close the real-world implementations come. I also derive a design space, centered around time, items and listeners, for this specific type of data and shortcomings of the real-world data regarding the previously identified contextual factors. The main part of this dissertation describes the design, implementation and evaluation of visualizations for listening histories. The first set of visualizations presents listening histories in the context of lifelogging, to allow analysing one’s behavior and reminiscing. These casual information visualizations vary in complexity and purpose. The second set is more concerned with the musical context and the idea that listening histories also represent relationships between musical items. I present approaches for improving music recommendation through interaction and integrating listening histories in regular media players. The main contributions of this thesis to HCI and information visualization are: First, a deeper understanding of relevant aspects and important patterns that make a person’s listening special and unique. Second, visualization prototypes and a design space of listening history visualizations that show approaches how to work with temporal personal data in a lifelogging context. Third, ways to improve recommender systems and existing software through the notion of seeing relationships between musical items in listening histories. Finally, as a meta-contribution, the casual approach of all visualizations also helps in providing non-experts with access to their own data, a future challenge for researchers and practitioners alike

Integrating Network Analysis and Data Mining Techniques into Effective Framework for Web Mining and Recommendation. A Framework for Web Mining and Recommendation

The main motivation for the study described in this dissertation is to benefit from the development in technology and the huge amount of available data which can be easily captured, stored and maintained electronically. We concentrate on Web usage (i.e., log) mining and Web structure mining. Analysing Web log data will reveal valuable feedback reflecting how effective the current structure of a web site is and to help the owner of a web site in understanding the behaviour of the web site visitors. We developed a framework that integrates statistical analysis, frequent pattern mining, clustering, classification and network construction and analysis. We concentrated on the statistical data related to the visitors and how they surf and pass through the various pages of a given web site to land at some target pages. Further, the frequent pattern mining technique was used to study the relationship between the various pages constituting a given web site. Clustering is used to study the similarity of users and pages. Classification suggests a target class for a given new entity by comparing the characteristics of the new entity to those of the known classes. Network construction and analysis is also employed to identify and investigate the links between the various pages constituting a Web site by constructing a network based on the frequency of access to the Web pages such that pages get linked in the network if they are identified in the result of the frequent pattern mining process as frequently accessed together. The knowledge discovered by analysing a web site and its related data should be considered valuable for online shoppers and commercial web site owners. Benefitting from the outcome of the study, a recommendation system was developed to suggest pages to visitors based on their profiles as compared to similar profiles of other visitors. The conducted experiments using popular datasets demonstrate the applicability and effectiveness of the proposed framework for Web mining and recommendation. As a by product of the proposed method, we demonstrate how it is effective in another domain for feature reduction by concentrating on gene expression data analysis as an application with some interesting results reported in Chapter 5

Concordancing Software in Practice: An investigation of searches and translation problems across EU official languages

2011/2012The present work reports on an empirical study aimed at investigating translation problems across multiple language pairs. In particular, the analysis is aimed at developing a methodological approach to study concordance search logs taken as manifestations of translation problems and, in a wider perspective, information needs. As search logs are a relatively unexplored data type within translation process research, a controlled environment was needed in order to carry out this exploratory analysis without incurring in additional problems caused by an excessive amount of variables. The logs were collected at the European Commission and contain a large volume of searches from English into 20 EU languages that staff translators working for the EU translation services submitted to an internally available multilingual concordancer. The study attempts to (i) identify differences in the searches (i.e. problems) based on the language pairs; and (ii) group problems into types. Furthermore, the interactions between concordance users and the tool itself have been examined to provide a translation-oriented perspective on the domain of Human-Computer Interaction. The study draws on the literature on translation problems, Information Retrieval and Web search log analysis, moving from the assumption that in the perspective of concordance searching, translation problems are best interpreted as information needs for which the concordancer is chosen as a form of external support. The structure of a concordance search is examined in all its parts and is eventually broken down into two main components: the 'Search Strategy' component and the 'Problem Unit' component. The former was further analyzed using a mainly quantitative approach, whereas the latter was addressed from a more qualitative perspective. The analysis of the Problem Unit takes into account the length of the search strings as well as their content and linguistic form, each addressed with a different methodological approach. Based on the understanding of concordance searches as manifestations of translation problems, a user- centered classification of translation-oriented information needs is developed to account for as many "problem" scenarios as possible. According to the initial expectations, different languages should experience different problems. This assumption could not be verified: the 20 different language pairs considered in this study behaved consistently on many levels and, due to the specific research environment, no definite conclusions could be reached as regards the role of the language family criterion for problem identification. The analysis of the 'Problem Unit' component has highlighted automatized support for translating Named Entities as a possible area for further research in translation technology and the development of computer-based translation support tools. Finally, the study indicates (concordance) search logs as an additional data type to be used in experiments on the translation process and for triangulation purposes, while drawing attention on the concordancer as a type of translation aid to be further fine-tuned for the needs of professional translators. ***Il presente lavoro consiste in uno studio empirico sui problemi di traduzione che emergono quando si considerano diverse coppie di lingue e in particolare sviluppa una metodologia per analizzare i log di ricerche effettuate dai traduttori in un software di concordanza (concordancer) quali manifestazioni di problemi di traduzione che, visti in una prospettiva più ampia, si possono anche considerare dei "bisogni d'informazione" (information needs). I log di ricerca costituiscono una tipologia di dato ancora relativamente nuova e inesplorata nell'ambito delle ricerche sul processo di traduzione e pertanto è emersa la necessità di svolgere un'analisi di tipo esplorativo in un contesto controllato onde evitare le problematiche aggiuntive derivanti da un numero eccessivo di variabili. I log di ricerca sono stati raccolti presso la Commissione europea e contengono quantitativi ingenti di ricerche effettuate dai traduttori impiegati presso i servizi di traduzione dell'Unione europea in un concordancer multilingue disponibile come risorsa interna. L'analisi si propone di individuare le differenze nelle ricerche (e quindi nei problemi) a seconda della coppia di lingue selezionata e di raggruppare tali problemi in tipologie. Lo studio fornisce inoltre informazioni sulle modalità di interazione tra gli utenti e il software nell'ambito di un contesto traduttivo, contribuendo alla ricerca nel campo dell'interazione uomo-macchina (Human-Computer Interaction). Il presente studio trae spunto dalla letteratura sui problemi di traduzione, sull'estrazione d'informazioni (Information Retrieval) e sulle ricerche nel Web e si propone di considerare i problemi di traduzione associati all'impiego di uno strumento per le concordanze quali bisogni di informazione per i quali lo strumento di concordanze è stato scelto come forma di supporto esterna. Ogni singola ricerca è stata esaminata e scomposta in due elementi principali: la "strategia di ricerca" (Search Strategy) e l'"unità problematica" (Problem Unit) che vengono studiati rispettivamente usando approcci prevalentemente di tipo quantitativo e qualitativo. L'analisi dell'unità problematica prende in considerazione la lunghezza, il contenuto e la forma linguistica delle stringhe, analizzando ciascuna con una metodologia di lavoro appositamente studiata. Avendo interpretato le ricerche di concordanze quali manifestazioni di bisogni d'informazione, l'analisi prosegue con la definizione di una serie di categorie di bisogni d'informazione (o problemi) legati alla traduzione e incentrati sul singolo utente al fine di includere quanti più scenari di ricerca possibile. L'assunto iniziale in base al quale lingue diverse manifesterebbero problemi diversi non è stato verificato empiricamente in quanto le 20 coppie di lingue esaminate hanno mostrato comportamenti alquanto similari nei diversi livelli di analisi. Vista la peculiarità dei dati utilizzati e la specificità dell'Unione europea come contesto di ricerca, non è stato possibile ottenere conclusioni definitive in merito al ruolo delle famiglie linguistiche quali indicatori di problemi, rispetto ad altri criteri di classificazione. L'analisi dell'unità problematica ha evidenziato le entità denominate (Named Entities) quale possibile oggetto di futuri progetti di ricerca nell'ambito delle tecnologie della traduzione. Oltre a offrire un contributo per i futuri sviluppi nell'ambito dei supporti informatici alla traduzione, con il presente studio si è voluto altresì presentare i log delle ricerche (di concordanze) quale tipologia aggiuntiva di dati per lo studio del processo di traduzione e per la triangolazione dei risultati empirico-sperimentali, cercando anche di suggerire possibili tratti migliorativi dei software di concordanza sulla base dei bisogni di informazione riscontrati nei traduttori.XXV Ciclo198

Analyzing Granger causality in climate data with time series classification methods

Attribution studies in climate science aim for scientifically ascertaining the influence of climatic variations on natural or anthropogenic factors. Many of those studies adopt the concept of Granger causality to infer statistical cause-effect relationships, while utilizing traditional autoregressive models. In this article, we investigate the potential of state-of-the-art time series classification techniques to enhance causal inference in climate science. We conduct a comparative experimental study of different types of algorithms on a large test suite that comprises a unique collection of datasets from the area of climate-vegetation dynamics. The results indicate that specialized time series classification methods are able to improve existing inference procedures. Substantial differences are observed among the methods that were tested