@phdthesis{Krinke2003, author = {Krinke, Jens}, title = {Advanced Slicing of Sequential and Concurrent Programs}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-375}, school = {Universit{\"a}t Passau}, year = {2003}, abstract = {Program slicing is a technique to identify statements that may influence the computations in other statements. Despite the ongoing research of almost 25 years, program slicing still has problems that prevent a widespread use: Sometimes, slices are too big to understand and too expensive and complicated to be computed for real-life programs. This thesis presents solutions to these problems: It contains various approaches which help the user to understand a slice more easily by making it more focused on the user's problem. All of these approaches have been implemented in the VALSOFT system and thorough evaluations of the proposed algorithms are presented. The underlying data structures used for slicing are program dependence graphs. They can also be used for different purposes: A new approach to clone detection based on identifying similar subgraphs in program dependence graphs is presented; it is able to detect modified clones better than other tools. In the theoretical part, this thesis presents a high-precision approach to slice concurrent procedural programs despite that optimal slicing is known to be undecidable. It is the first approach to slice concurrent programs that does not rely on inlining of called procedures.}, subject = {Programmanalyse}, language = {en} } @phdthesis{Wiesner2004, author = {Wiesner, Christian}, title = {Query Evaluation Techniques for Data Integration Systems}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-406}, school = {Universit{\"a}t Passau}, year = {2004}, abstract = {In this work we present novel query evaluation techniques for data integration systems in different environments, ranging from a central data-warehouse approach, over distributed virtual market places, to peer-to-peer (P2P) systems. Based on a new distributed evaluation technique, the so-called HyperQueries, we present a reference architecture for distributed virtual market places. These HyperQueries enable us to dynamically construct query evaluation plans by referencing sub-plans in the Internet. Furthermore, the process of data integration is structured. Subsequently, we investigate P2P data integration systems without central instances. We introduce so-called Super-Peers which structure a P2P network. Using this Super-Peer based network we "unroll" queries. This allows us to execute even user-defined operators nearby the data sources. Finally, we propose novel, efficient join algorithms for decision support queries in central data-warehouse systems. The proposed order-preserving hashjoins and generalized hashteams are based on early sorting and early partitioning of the inputs and can speed up the query evaluation up to orders of magnitutes.}, subject = {Abfrageverarbeitung}, language = {en} } @phdthesis{Bachmaier2004, author = {Bachmaier, Christian}, title = {Circle Planarity of Level Graphs}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus-385}, school = {Universit{\"a}t Passau}, year = {2004}, abstract = {In this dissertation we generalise the notion of level planar graphs in two directions: track planarity and radial planarity. Our main results are linear time algorithms both for the planarity test and for the computation of an embedding, and thus a drawing. Our algorithms use and generalise PQ-trees, which are a data structure for efficient planarity tests.}, subject = {Graphentheorie}, language = {en} } @article{PetitCerqueusBoutetetal.2016, author = {Petit, Albin and Cerqueus, Thomas and Boutet, Antoine and Ben Mokhtar, Sonia and Coquil, David and Brunie, Lionel and Kosch, Harald}, title = {SimAttack: private web search under fire}, series = {Journal of Internet Services and Applications}, journal = {Journal of Internet Services and Applications}, publisher = {SpringerOpen}, issn = {1869-0238}, doi = {10.1186/s13174-016-0044-x}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:739-opus4-3574}, year = {2016}, abstract = {Web Search engines have become an indispensable online service to retrieve content on the Internet. However, using search engines raises serious privacy issues as the latter gather large amounts of data about individuals through their search queries. Two main techniques have been proposed to privately query search engines. A first category of approaches, called unlinkability, aims at disassociating the query and the identity of its requester. A second category of approaches, called indistinguishability, aims at hiding user's queries or user's interests by either obfuscating user's queries, or forging new fake queries. This paper presents a study of the level of protection offered by three popular solutions: Tor-based, TrackMeNot, and GooPIR. For this purpose, we present an efficient and scalable attack - SimAttack - leveraging a similarity metric to capture the distance between preliminary information about the users (i.e., history of query) and a new query. SimAttack de-anonymizes up to 36.7 \% of queries protected by an unlinkability solution (i.e., Tor-based), and identifies up to 45.3 and 51.6 \% of queries protected by indistinguishability solutions (i.e., TrackMeNot and GooPIR, respectively). In addition, SimAttack de-anonymizes 6.7 \% more queries than state-of-the-art attacks and dramatically improves the performance of the attack on TrackMeNot by 23.6 \%, while retaining an execution time faster by two orders of magnitude.}, language = {en} }