A Multiagent System for Dynamic Data Aggregation in Medical Research

The collection of medical data for research purposes is a challenging and long-lasting process. In an effort to accelerate and facilitate this process we propose a new framework for dynamic aggregation of medical data from distributed sources. We use agent-based coordination between medical and research institutions. Our system employs principles of peer-to-peer network organization and coordination models to search over already constructed distributed databases and to identify the potential contributors when a new database has to be built. Our framework takes into account both the requirements of a research study and current data availability. This leads to better definition of database characteristics such as schema, content, and privacy parameters. We show that this approach enables a more efficient way to collect data for medical research.

Privacy - Preserving Data Exchange and Aggregation in Healthcare

Alevtina Dubovitskaya

Medical data are often scattered among multiple clinics, hospitals, insurance companies, pharmacies, and research institutions that store and process personal healthcare information. The use of information and communication technologies for health (eHealth) provides us with the means to share healthcare data between authorized parties in an efficient manner. In this thesis, we address some of the challenges of implementing eHealth in practice: to achieve interoperability between data sources, and to ensure privacy for patients. Achieving both of these guarantees is our goal but they seem conflictual, hence the challenge. Once interoperability is achieved and a patientâs data are shared, it becomes evenmore difficult to ensure the patientâs privacy i.e., to provide to a patient control over his data and to guarantee the data anonymity in medical research. We address the aforementioned challenges by studying requirements from medical and legal perspectives, and by developing algorithms and frameworks to support privacy-preserving dynamic data-sharing, exchange, and aggregation from multiple data sources. In the first part of the thesis, we address certain privacy challenges. We present a framework based on the blockchain technology for ensuring traceability and accountability when sharing, exchanging, and aggregating medical data. Our framework ensures privacy, security, availability, and fine-grained access control over highly sensitive patient-data. We also analyze the potential of applying blockchain technology in different eHealth settings: primary care, medical-data research, and connected health. Our second contribution is a framework for privacy-preserving data aggregation: an algorithm for constructing the anonymized database and a protocol that improves the utility of the anonymized database as the database grows. In the second part of the thesis, we focus on achieving interoperability. We design an interface specification that defines communication protocols andmessages supporting integration of a new software tool in clinical practice. Then, we develop a multi-agent system (MAS) for the dynamic aggregation of the data collected and generated by this software tool for the purpose of clinical research. This MAS takes into account the objectives of the research study, the availability of data, and could employ our proposed algorithm for privacy-preserving data aggregation. The negotiation protocol in the framework of theMAS achieves a precise definition of database characteristics, such as schema, content, and privacy parameters, therefore increasing the efficiency of data collection for medical research and ensuring the privacy of patients.

EPFL2018

Towards a Foundation Model for Peer-to-Peer Web Information

Karl Aberer, Jie Wu

We find that there lacks a formal algebraic framework in the research area of P2P information retrieval. Such a formal framework is indispensable and pivotal. On the one hand, no solid theoretical foundation can explain why the results of many ad-hoc commercial ranking algorithms are good or bad; on the other hand, in some cases, it might be preferable in a decentralized search system to use different retrieval models and different ranking algorithms at the same time since each separate document collection and each peer might have different characteristics. Thus it is important to have a common framework, where we can capture the individual models and describe the overall behavior. Such a framework characterizes notions like ranking, relevance feedback, rank aggregation and combination, etc. and necessary operations. In this paper, we define such a foundation model for P2P information retrieval, where data models for rankings from the perspectives of both the end user's search needs and the search member server's contextual rankings are provided, and a new ranking aggregation language is proposed to perform ranking combination operations. A case study is included to demonstrate how the foundation model and the ranking aggregation language could be applied in real ranking problems of P2P Web search systems.

2004

Distributed link-based ranking in P2P Web retrieval

Jie Wu

One of the main differences between modern search engines and traditional ones is the adoption of link-based ranking algorithm in ordering Web documents. Google has claimed that it is its link-based ranking algorithm, PageRank that has made the quality of its search results superior. However, existing link-based ranking algorithms are mostly logically centralized although techniques of distributed data management and load balancing have been used in search engines to improve the performance and availability of the systems. With the scale of the Web becoming larger and larger, the scalability of traditional search engines is very much limited by the current centralized algorithms, models, and architectures. The centralization in link-based ranking computation has brought in several critical problems that are hard to solve: centralized bottleneck and single point of failure, prohibitively high computation cost, lag in availability of fresh information, etc. In response to these problems, we have explored several approaches to address them: incremental computation, new distributed model based algorithms, and a common decentralized framework. In particular, we have proposed the new distributed approach based on a Layered Markov Model to distinguish stochastic transitions among Web sites and Web documents. Based on this model, we propose two different methods for computation of ranking of Web documents, a centralized one and a decentralized one. Both produce a well-defined ranking for a given Web graph. We then formally prove that the two approaches are equivalent. This provides a theoretical foundation for decomposing link-based rank computation and makes the computation for a Web-scale graph feasible in a decentralized fashion, such as required for Web search engines having a Peer-to-Peer (P2P) architecture. Furthermore, personalized rankings can be produced by adapting the computation at both the local layer and the global layer. The empirical results show that the ranking generated by our model is qualitatively comparable to or even better than the ranking produced by PageRank. On the other hand, the common framework for Peer-to-Peer Information Retrieval (IR) is situated in a more general scope. It captures the essence of individual models and describes the overall behavior of P2P Web retrieval systems. Such a framework characterizes notions like ranking, ranking aggregation and combination, etc. Algebraic properties of them are explored and guidelines for ranking computation based on those properties are proposed. Application scenarios are then given to show how different search engines and their algorithms can be formalized within this common framework. As two representative examples, heuristic and model-guided distributed ranking compositions are elaborated to demonstrate the power and potentials of this common framework. Results of my research work can be used in modern search companies to build a truly distributed search engine system; they also form a solid base for future research on topics of distributed ranking computation for P2P Web retrieval, including specific layered decentralized algorithms, and problems within the general common framework.