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Auflistung nach Autor:in "Grebhahn, Alexander"

1 - 6 von 6
  • Zeitschriftenartikel
    BTW 2013 – Zwischen wissenschaftlicher Geschichte und moderner Herausforderung
    (Datenbank-Spektrum: Vol. 13, No. 2, 2013) Köppen, Veit; Schäler, Martin; Grebhahn, Alexander; Saake, Gunter
  • Konferenzbeitrag
    Distance-Based Sampling of Software Configuration Spaces
    (Software Engineering 2020, 2020) Kaltenecker, Christian; Grebhahn, Alexander; Siedmund, Norbert; Guo, Jianmei; Apel, Sven
    Configurable software systems provide configuration options to adjust and optimize their functional and non-functional properties. However, to obtain accurate performance predictions, a representative sample set of configurations is required. Different sampling strategies have been proposed, which come with different advantages and disadvantages. In our experiments, we found that most sampling strategies do not achieve a good coverage of the configuration space with respect to covering relevant performance values. That is, they miss important configurations with distinct performance behavior. Based on this observation, we devise a new sampling strategy that is based on a distance metric and a probability distribution to spread the configurations of the sample set across the configuration space. To demonstrate the merits of distance-based sampling, we compare it to state-of-the-art sampling strategies on 10 real-world configurable software systems. Our results show that distance-based sampling leads to more accurate performance models for medium to large sample sets.
  • Konferenzbeitrag
    Extending an index-benchmarking framework with non-invasive visualization capability
    (Datenbanksysteme für Business, Technologie und Web (BTW) 2013 - Workshopband, 2013) Broneske, David; Schäler, Martin; Grebhahn, Alexander
    Finding a suitable multi-dimensional index structure for a data-intensive system is not a trivial task. The QuEval framework supports users in finding the best index structure from a list of candidates. Nevertheless, if an index structure shows itself superior to other index structures most oft the times, but fails for one data set, we want to know the reason for this phenomenon. To support an understanding of deficits, a visualization of the partitioning scheme is helpful. Consequently, we propose a visualization component which interacts with QuEval without affecting the performance evaluation. Thus, we use a modern software-engineering approach based on AspectJ to support Digital Engineering of complex solutions.
  • Konferenzbeitrag
    Performance-Influence Models
    (Software Engineering 2016, 2016) Siegmund, Norbert; Grebhahn, Alexander; Apel, Sven; Kästner, Christian
  • Konferenzbeitrag
    Privacy-aware multidimensional indexing
    (Datenbanksysteme für Business, Technologie und Web (BTW) 2022, 2013) Grebhahn, Alexander; Schäler, Martin; Köppen, Veit; Saake, Gunter
    Deleting data from a database system in a forensic secure environment and in a high performant way is a complex challenge. Due to redundant copies and additional information stored about data items, it is not appropriate to delete only data items themselves. Additional challenges arise when using multidimensional index structures. This is because information of data items are used to index the space. As initial result, we present different deletion levels, to overcome this challenge. Based on this classification, we analyze how data can be reconstructed from the index and modify index structures to improve privacy of data items. Second, we benchmark our index structure modifications and quantify our modifications. Our results indicate that forensic secure deletion is possible with modification of multidimensional index structures having only a small impact on computational performance, in some cases.
  • Konferenzbeitrag
    Secure Deletion: Towards Tailor-Made Privacy in Database Systems
    (Datenbanksysteme für Business, Technologie und Web (BTW) 2013 - Workshopband, 2013) Grebhahn, Alexander; Schäler, Martin; Köppen, Veit
    In order to ensure a secure data life cycle, it is necessary to delete sensitive data in a forensic secure way. Current state of the art in common database systems is not to provide secure deletion at all. There exist academic demonstrators that address some aspects of secure deletion. However, they are limited to their deletion approach. We argue, due to different data sensitivity levels (probably even on attribute level) and differences in policies (e.g., time when and how a data item has to be deleted), it is necessary to have a standardized, user defined opportunity to enforce secure data deletion in a forensic secure manner. Our literature analysis reveals that most approaches are based on overwriting the data. Thus, in this paper, we examine how it is possible to integrate user-defined overwriting procedures to allow a customizable deletion process based on existing default interfaces to minimize the integration overhead. In general, we propose an extension of SQL and a page propagation strategy allowing the integration of a user defined deletion procedure.