@article{LamprechtWickertMargaria2014,
  author    = {Lamprecht, Anna-Lena and Wickert, Alexander and Margaria, Tiziana},
  title     = {Lessons Learned},
  series = {Process Design for Natural Scientists: an agile model-driven approach},
  journal   = {Process Design for Natural Scientists: an agile model-driven approach},
  number    = {500},
  editor    = {Lambrecht, Anna-Lena and Margaria, Tiziana},
  publisher = {Springer Verlag},
  address   = {Berlin},
  isbn      = {978-3-662-45005-5},
  issn      = {1865-0929},
  pages     = {45 -- 64},
  year      = {2014},
  abstract  = {This chapter summarizes the experience and the lessons we learned concerning the application of the jABC as a framework for design and execution of scientific workflows. It reports experiences from the domain modeling (especially service integration) and workflow design phases and evaluates the resulting models statistically with respect to the SIB library and hierarchy levels.},
  language  = {en}
}
@article{LamprechtWickert2014,
  author    = {Lamprecht, Anna-Lena and Wickert, Alexander},
  title     = {The Course's SIB Libraries},
  series = {Process Design for Natural Scientists: an agile model-driven approach},
  journal   = {Process Design for Natural Scientists: an agile model-driven approach},
  number    = {500},
  editor    = {Lambrecht, Anna-Lena and Margaria, Tiziana},
  publisher = {Springer Verlag},
  address   = {Berlin},
  isbn      = {978-3-662-45005-5},
  issn      = {1865-0929},
  pages     = {30 -- 44},
  year      = {2014},
  abstract  = {This chapter gives a detailed description of the service framework underlying all the example projects that form the foundation of this book. It describes the different SIB libraries that we made available for the course "Process modeling in the natural sciences" to provide the functionality that was required for the envisaged applications. The students used these SIB libraries to realize their projects.},
  language  = {en}
}
@article{LamprechtMargaria2015,
  author    = {Lamprecht, Anna-Lena and Margaria, Tiziana},
  title     = {Scientific workflows and XMDD},
  series = {Process design for natural scientists},
  journal   = {Process design for natural scientists},
  editor    = {Lamprecht, Anna-Lena and Margaria, Tiziana},
  publisher = {Springer},
  address   = {Berlin},
  isbn      = {978-3-662-45006-2},
  pages     = {1 -- 13},
  year      = {2015},
  language  = {en}
}
@article{NaujokatNeubauerLamprechtetal.2014,
  author    = {Naujokat, Stefan and Neubauer, Johannes and Lamprecht, Anna-Lena and Steffen, Bernhard and Joerges, Sven and Margaria, Tiziana},
  title     = {Simplicity-first model-based plug-in development},
  series = {Software : practice \& experience},
  volume    = {44},
  journal   = {Software : practice \& experience},
  number    = {3},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {0038-0644},
  doi       = {10.1002/spe.2243},
  pages     = {277 -- 297},
  year      = {2014},
  abstract  = {In this article, we present our experience with over a decade of strict simplicity orientation in the development and evolution of plug-ins. The point of our approach is to enable our graphical modeling framework jABC to capture plug-in development in a domain-specific setting. The typically quite tedious and technical plug-in development is shifted this way from a programming task to the modeling level, where it can be mastered also by application experts without programming expertise. We show how the classical plug-in development profits from a systematic domain-specific API design and how the level of abstraction achieved this way can be further enhanced by defining adequate building blocks for high-level plug-in modeling. As the resulting plug-in models can be compiled and deployed automatically, our approach decomposes plug-in development into three phases where only the realization phase requires plug-in-specific effort. By using our modeling framework jABC, this effort boils down to graphical, tool-supported process modeling. Furthermore, we support the automatic completion of process sketches for executability. All this will be illustrated along the most recent plug-in-based evolution of the jABC framework, which witnessed quite some bootstrapping effects.},
  language  = {en}
}
@book{LamprechtMagariaSteffenetal.2007,
  author    = {Lamprecht, Anna-Lena and Magaria, Tiziana and Steffen, Bernhard and Sczyrba, Alexander and Hartmeier, Sven and Giegerich, Robert},
  title     = {GeneFisher-P},
  series = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Informatik},
  volume    = {2007, 3},
  journal   = {Preprint / Universit{\"a}t Potsdam, Institut f{\"u}r Informatik},
  publisher = {Univ.},
  address   = {Potsdam},
  issn      = {0946-7580},
  pages     = {17 S.},
  year      = {2007},
  language  = {en}
}
@misc{Schroeter2024,
  type      = {Master Thesis},
  author    = {Schr{\"o}ter, Alexander},
  title     = {Erstellung und Evaluation eines Fragebogens zur Erfassung von komplexen Interaktionssituationen in Software-Entwicklungsprojekten},
  doi       = {10.25932/publishup-63187},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-631873},
  school      = {Universit{\"a}t Potsdam},
  pages     = {75},
  year      = {2024},
  abstract  = {Die fortschreitende Digitalisierung durchzieht immer mehr Lebensbereiche und f{\"u}hrt zu immer komplexeren sozio-technischen Systemen. Obwohl diese Systeme zur Lebenserleichterung entwickelt werden, k{\"o}nnen auch unerw{\"u}nschte Nebeneffekte entstehen. Ein solcher Nebeneffekt k{\"o}nnte z.B. die Datennutzung aus Fitness-Apps f{\"u}r nachteilige Versicherungsentscheidungen sein. Diese Nebeneffekte manifestieren sich auf allen Ebenen zwischen Individuum und Gesellschaft. Systeme mit zuvor unerwarteten Nebeneffekten k{\"o}nnen zu sinkender Akzeptanz oder einem Verlust von Vertrauen f{\"u}hren. Da solche Nebeneffekte oft erst im Gebrauch in Erscheinung treten, bedarf es einer besonderen Betrachtung bereits im Konstruktionsprozess. Mit dieser Arbeit soll ein Beitrag geleistet werden, um den Konstruktionsprozess um ein geeignetes Hilfsmittel zur systematischen Reflexion zu erg{\"a}nzen. In vorliegender Arbeit wurde ein Analysetool zur Identifikation und Analyse komplexer Interaktionssituationen in Software-Entwicklungsprojekten entwickelt. Komplexe Interaktionssituationen sind von hoher Dynamik gepr{\"a}gt, aus der eine Unvorhersehbarkeit der Ursache-Wirkungs-Beziehungen folgt. Hierdurch k{\"o}nnen die Akteur*innen die Auswirkungen der eigenen Handlungen nicht mehr {\"u}berblicken, sondern lediglich im Nachhinein rekonstruieren. Hieraus k{\"o}nnen sich fehlerhafte Interaktionsverl{\"a}ufe auf vielf{\"a}ltigen Ebenen ergeben und oben genannte Nebeneffekte entstehen. Das Analysetool unterst{\"u}tzt die Konstrukteur*innen in jeder Phase der Entwicklung durch eine angeleitete Reflexion, um potenziell komplexe Interaktionssituationen zu antizipieren und ihnen durch Analyse der m{\"o}glichen Ursachen der Komplexit{\"a}tswahrnehmung zu begegnen. Ausgehend von der Definition f{\"u}r Interaktionskomplexit{\"a}t wurden Item-Indikatoren zur Erfassung komplexer Interaktionssituationen entwickelt, die dann anhand von geeigneten Kriterien f{\"u}r Komplexit{\"a}t analysiert werden. Das Analysetool ist als „Do-It-Yourself" Fragebogen mit eigenst{\"a}ndiger Auswertung aufgebaut. Die Genese des Fragebogens und die Ergebnisse der durchgef{\"u}hrten Evaluation an f{\"u}nf Softwarentwickler*innen werden dargestellt. Es konnte festgestellt werden, dass das Analysetool bei den Befragten als anwendbar, effektiv und hilfreich wahrgenommen wurde und damit eine hohe Akzeptanz bei der Zielgruppe genießt. Dieser Befund unterst{\"u}tzt die gute Einbindung des Analysetools in den Software-Entwicklungsprozess.},
  language  = {de}
}
@article{MarcoFigueraRiedelRossietal.2022,
  author    = {Marco Figuera, Ramiro and Riedel, Christian and Rossi, Angelo Pio and Unnithan, Vikram},
  title     = {Depth to diameter analysis on small simple craters at the lunar south pole - possible implications for ice harboring},
  series = {Remote sensing},
  volume    = {14},
  journal   = {Remote sensing},
  number    = {3},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2072-4292},
  doi       = {10.3390/rs14030450},
  pages     = {13},
  year      = {2022},
  abstract  = {In this paper, we present a study comparing the depth to diameter (d/D) ratio of small simple craters (200-1000 m) of an area between -88.5 degrees to -90 degrees latitude at the lunar south pole containing Permanent Shadowed Regions (PSRs) versus craters without PSRs. As PSRs can reach temperatures of 110 K and are capable of harboring volatiles, especially water ice, we analyzed the relationship of depth versus diameter ratios and its possible implications for harboring water ice. Variations in the d/D ratios can also be caused by other processes such as degradation, isostatic adjustment, or differences in surface properties. The conducted d/D ratio analysis suggests that a differentiation between craters containing PSRs versus craters without PSRs occurs. Thus, a possible direct relation between d/D ratio, PSRs, and water ice harboring might exist. Our results suggest that differences in the target's surface properties may explain the obtained results. The resulting d/D ratios of craters with PSRs can help to select target areas for future In-Situ Resource Utilization (ISRU) missions.},
  language  = {en}
}
@article{LuckeHaferHartmann2020,
  author    = {Lucke, Ulrike and Hafer, J{\"o}rg and Hartmann, Niklas},
  title     = {Strategieentwicklung in der Hochschule als partizipativer Prozess},
  series = {Potsdamer Beitr{\"a}ge zur Hochschulforschung},
  journal   = {Potsdamer Beitr{\"a}ge zur Hochschulforschung},
  number    = {6},
  publisher = {Universit{\"a}tsverlag Potsdam},
  address   = {Potsdam},
  isbn      = {978-3-86956-498-2},
  issn      = {2192-1075},
  doi       = {10.25932/publishup-49276},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-492764},
  pages     = {99 -- 117},
  year      = {2020},
  abstract  = {Die Setzung strategischer Ziele sowie die Zuordnung und Umsetzung dazugeh{\"o}render Maßnahmen sind ein wesentliches Element, um die Innovationsf{\"a}higkeit von Organisationen zu erhalten. In den vergangenen Jahren ist auch an Hochschulen die Strategiebildung deutlich vorangetrieben worden. Dies betrifft verschiedene Handlungsfelder, und es werden verschiedene Ans{\"a}tze verfolgt. Der vorliegende Beitrag greift am Beispiel der Universit{\"a}t Potsdam drei in den vergangenen Jahren adressierte Strategiebereiche heraus: IT, E-Learning und Forschungsdaten. Die damit verbundenen Prozesse waren in unterschiedlichem Maß von Partizipation gepr{\"a}gt. Die gesammelten Erfahrungen werden reflektiert, und es werden Empfehlungen f{\"u}r Strategieentwicklungsprozesse abgeleitet.},
  language  = {de}
}
@phdthesis{Jiang2007,
  author    = {Jiang, Chunyan},
  title     = {Multi-visualization and hybrid segmentation approaches within telemedicine framework},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12829},
  school      = {Universit{\"a}t Potsdam},
  year      = {2007},
  abstract  = {The innovation of information techniques has changed many aspects of our life. In health care field, we can obtain, manage and communicate high-quality large volumetric image data by computer integrated devices, to support medical care. In this dissertation I propose several promising methods that could assist physicians in processing, observing and communicating the image data. They are included in my three research aspects: telemedicine integration, medical image visualization and image segmentation. And these methods are also demonstrated by the demo software that I developed. One of my research point focuses on medical information storage standard in telemedicine, for example DICOM, which is the predominant standard for the storage and communication of medical images. I propose a novel 3D image data storage method, which was lacking in current DICOM standard. I also created a mechanism to make use of the non-standard or private DICOM files. In this thesis I present several rendering techniques on medical image visualization to offer different display manners, both 2D and 3D, for example, cut through data volume in arbitrary degree, rendering the surface shell of the data, and rendering the semi-transparent volume of the data. A hybrid segmentation approach, designed for semi-automated segmentation of radiological image, such as CT, MRI, etc, is proposed in this thesis to get the organ or interested area from the image. This approach takes advantage of the region-based method and boundary-based methods. Three steps compose the hybrid approach: the first step gets coarse segmentation by fuzzy affinity and generates homogeneity operator; the second step divides the image by Voronoi Diagram and reclassifies the regions by the operator to refine segmentation from the previous step; the third step handles vague boundary by level set model. Topics for future research are mentioned in the end, including new supplement for DICOM standard for segmentation information storage, visualization of multimodal image information, and improvement of the segmentation approach to higher dimension.},
  language  = {en}
}
@phdthesis{Hu2006,
  author    = {Hu, Ji},
  title     = {A virtual machine architecture for IT-security laboratories},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7818},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {This thesis discusses challenges in IT security education, points out a gap between e-learning and practical education, and presents a work to fill the gap. E-learning is a flexible and personalized alternative to traditional education. Nonetheless, existing e-learning systems for IT security education have difficulties in delivering hands-on experience because of the lack of proximity. Laboratory environments and practical exercises are indispensable instruction tools to IT security education, but security education in conventional computer laboratories poses particular problems such as immobility as well as high creation and maintenance costs. Hence, there is a need to effectively transform security laboratories and practical exercises into e-learning forms. In this thesis, we introduce the Tele-Lab IT-Security architecture that allows students not only to learn IT security principles, but also to gain hands-on security experience by exercises in an online laboratory environment. In this architecture, virtual machines are used to provide safe user work environments instead of real computers. Thus, traditional laboratory environments can be cloned onto the Internet by software, which increases accessibility to laboratory resources and greatly reduces investment and maintenance costs. Under the Tele-Lab IT-Security framework, a set of technical solutions is also proposed to provide effective functionalities, reliability, security, and performance. The virtual machines with appropriate resource allocation, software installation, and system configurations are used to build lightweight security laboratories on a hosting computer. Reliability and availability of laboratory platforms are covered by a virtual machine management framework. This management framework provides necessary monitoring and administration services to detect and recover critical failures of virtual machines at run time. Considering the risk that virtual machines can be misused for compromising production networks, we present a security management solution to prevent the misuse of laboratory resources by security isolation at the system and network levels. This work is an attempt to bridge the gap between e-learning/tele-teaching and practical IT security education. It is not to substitute conventional teaching in laboratories but to add practical features to e-learning. This thesis demonstrates the possibility to implement hands-on security laboratories on the Internet reliably, securely, and economically.},
  subject      = {Computersicherheit},
  language  = {en}
}
@book{MeinelSack2012,
  author    = {Meinel, Christoph and Sack, Harald},
  title     = {Internetworking : technische Grundlagen und Anwendungen},
  publisher = {Springer-Verlag Berlin Heidelberg},
  address   = {Berlin, Heidelberg},
  isbn      = {978-3-540-92939-0},
  doi       = {10.1007/978-3-540-92940-6},
  pages     = {978 S.},
  year      = {2012},
  language  = {de}
}
@phdthesis{Ghasemzadeh2005,
  author    = {Ghasemzadeh, Mohammad},
  title     = {A new algorithm for the quantified satisfiability problem, based on zero-suppressed binary decision diagrams and memoization},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-6378},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {Quantified Boolean formulas (QBFs) play an important role in theoretical computer science. QBF extends propositional logic in such a way that many advanced forms of reasoning can be easily formulated and evaluated. In this dissertation we present our ZQSAT, which is an algorithm for evaluating quantified Boolean formulas. ZQSAT is based on ZBDD: Zero-Suppressed Binary Decision Diagram , which is a variant of BDD, and an adopted version of the DPLL algorithm. It has been implemented in C using the CUDD: Colorado University Decision Diagram package. The capability of ZBDDs in storing sets of subsets efficiently enabled us to store the clauses of a QBF very compactly and let us to embed the notion of memoization to the DPLL algorithm. These points led us to implement the search algorithm in such a way that we could store and reuse the results of all previously solved subformulas with a little overheads. ZQSAT can solve some sets of standard QBF benchmark problems (known to be hard for DPLL based algorithms) faster than the best existing solvers. In addition to prenex-CNF, ZQSAT accepts prenex-NNF formulas. We show and prove how this capability can be exponentially beneficial.},
  subject      = {Bin{\"a}res Entscheidungsdiagramm},
  language  = {en}
}
@phdthesis{Linckels2008,
  author    = {Linckels, Serge},
  title     = {An e-librarian service : supporting explorative learning by a description logics based semantic retrieval tool},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17452},
  school      = {Universit{\"a}t Potsdam},
  year      = {2008},
  abstract  = {Although educational content in electronic form is increasing dramatically, its usage in an educational environment is poor, mainly due to the fact that there is too much of (unreliable) redundant, and not relevant information. Finding appropriate answers is a rather difficult task being reliant on the user filtering of the pertinent information from the noise. Turning knowledge bases like the online tele-TASK archive into useful educational resources requires identifying correct, reliable, and "machine-understandable" information, as well as developing simple but efficient search tools with the ability to reason over this information. Our vision is to create an E-Librarian Service, which is able to retrieve multimedia resources from a knowledge base in a more efficient way than by browsing through an index, or by using a simple keyword search. In our E-Librarian Service, the user can enter his question in a very simple and human way; in natural language (NL). Our premise is that more pertinent results would be retrieved if the search engine understood the sense of the user's query. The returned results are then logical consequences of an inference rather than of keyword matchings. Our E-Librarian Service does not return the answer to the user's question, but it retrieves the most pertinent document(s), in which the user finds the answer to his/her question. Among all the documents that have some common information with the user query, our E-Librarian Service identifies the most pertinent match(es), keeping in mind that the user expects an exhaustive answer while preferring a concise answer with only little or no information overhead. Also, our E-Librarian Service always proposes a solution to the user, even if the system concludes that there is no exhaustive answer. Our E-Librarian Service was implemented prototypically in three different educational tools. A first prototype is CHESt (Computer History Expert System); it has a knowledge base with 300 multimedia clips that cover the main events in computer history. A second prototype is MatES (Mathematics Expert System); it has a knowledge base with 115 clips that cover the topic of fractions in mathematics for secondary school w.r.t. the official school programme. All clips were recorded mainly by pupils. The third and most advanced prototype is the "Lecture Butler's E-Librarain Service"; it has a Web service interface to respect a service oriented architecture (SOA), and was developed in the context of the Web-University project at the Hasso-Plattner-Institute (HPI). Two major experiments in an educational environment - at the Lyc{\´e}e Technique Esch/Alzette in Luxembourg - were made to test the pertinence and reliability of our E-Librarian Service as a complement to traditional courses. The first experiment (in 2005) was made with CHESt in different classes, and covered a single lesson. The second experiment (in 2006) covered a period of 6 weeks of intensive use of MatES in one class. There was no classical mathematics lesson where the teacher gave explanations, but the students had to learn in an autonomous and exploratory way. They had to ask questions to the E-Librarian Service just the way they would if there was a human teacher.},
  subject      = {Terminologische Logik},
  language  = {en}
}
@phdthesis{Huang2006,
  author    = {Huang, Wanjun},
  title     = {Temporary binding for dynamic middleware construction and web services composition},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7672},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {With increasing number of applications in Internet and mobile environments, distributed software systems are demanded to be more powerful and flexible, especially in terms of dynamism and security. This dissertation describes my work concerning three aspects: dynamic reconfiguration of component software, security control on middleware applications, and web services dynamic composition. Firstly, I proposed a technology named Routing Based Workflow (RBW) to model the execution and management of collaborative components and realize temporary binding for component instances. The temporary binding means component instances are temporarily loaded into a created execution environment to execute their functions, and then are released to their repository after executions. The temporary binding allows to create an idle execution environment for all collaborative components, on which the change operations can be immediately carried out. The changes on execution environment will result in a new collaboration of all involved components, and also greatly simplifies the classical issues arising from dynamic changes, such as consistency preserving etc. To demonstrate the feasibility of RBW, I created a dynamic secure middleware system - the Smart Data Server Version 3.0 (SDS3). In SDS3, an open source implementation of CORBA is adopted and modified as the communication infrastructure, and three secure components managed by RBW, are created to enhance the security on the access of deployed applications. SDS3 offers multi-level security control on its applications from strategy control to application-specific detail control. For the management by RBW, the strategy control of SDS3 applications could be dynamically changed by reorganizing the collaboration of the three secure components. In addition, I created the Dynamic Services Composer (DSC) based on Apache open source projects, Apache Axis and WSIF. In DSC, RBW is employed to model the interaction and collaboration of web services and to enable the dynamic changes on the flow structure of web services. Finally, overall performance tests were made to evaluate the efficiency of the developed RBW and SDS3. The results demonstrated that temporary binding of component instances makes slight impacts on the execution efficiency of components, and the blackout time arising from dynamic changes can be extremely reduced in any applications.},
  subject      = {Middleware},
  language  = {en}
}
@inproceedings{DennertMoellerGarmannKujathetal.2016,
  author    = {Dennert-M{\"o}ller, Elisabeth and Garmann, Robert and Kujath, Bertold and Zscheyge, Oliver and Weicker, Karsten and B{\"o}hne, Sebastian and Knobelsdorf, Maria and Kreitz, Christoph and Steen, Alexander and Wisniewski, Max and Benzm{\"u}ller, Christoph and Gebhardt, Kai and Ehlenz, Matthias and Bergner, Nadine and Schroeder, Ulrik},
  title     = {Hochschuldidaktik der Informatik},
  editor    = {Schwill, Andreas and Lucke, Ulrike},
  publisher = {Universit{\"a}tsverlag Potsdam},
  address   = {Potsdam},
  isbn      = {978-3-86956-376-3},
  issn      = {1868-0844},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-93511},
  pages     = {102},
  year      = {2016},
  abstract  = {Die 7. Fachtagung f{\"u}r Hochschuldidaktik, die 2016 erneut mit der DeLFI E-Learning Fachtagung Informatik stattfand, setzte das erfolgreiche Modell einer Tagung fort, die sich mit hochschuldidaktischen Fragen und der Gestaltung von Studieng{\"a}ngen der Informatik besch{\"a}ftigt. Thema der Tagung waren alle Fragen, die sich der Vermittlung von Informatikgegenst{\"a}nden im Hochschulbereich widmen. Dazu geh{\"o}rten u.a.: • fachdidaktische Konzepte der Vermittlung einzelner Informatikgegenst{\"a}nde • methodische L{\"o}sungen, wie spezielle Lehr- und Lernformen, Durchf{\"u}hrungskonzepte • empirische Ergebnisse und Vergleichsstudien • E-Learning-Ans{\"a}tze, wenn sie ein erkennbares didaktisches Konzept verfolgen • Studienkonzepte und Curricula, organisatorische Fragen, wie Gewinnung von Studierenden, Studieneingangsphase, Abbrecher. Die Fachtagung widmete sich ausgew{\"a}hlten Fragestellungen dieses Themenkomplexes, die durch Vortr{\"a}ge ausgewiesener Experten, durch eingereichte Beitr{\"a}ge und durch Pr{\"a}sentationen und Poster intensiv behandelt wurden. Unser besonderer Dank gilt dem Programmkomitee und den hier nicht genannten Helfern f{\"u}r ihren Einsatz bei der Vorbereitung und Durchf{\"u}hrung der Tagung.},
  language  = {de}
}
@phdthesis{Menzel2011,
  author    = {Menzel, Michael},
  title     = {Model-driven security in service-oriented architectures : leveraging security patterns to transform high-level security requirements to technical policies},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-59058},
  school      = {Universit{\"a}t Potsdam},
  year      = {2011},
  abstract  = {Service-oriented Architectures (SOA) facilitate the provision and orchestration of business services to enable a faster adoption to changing business demands. Web Services provide a technical foundation to implement this paradigm on the basis of XML-messaging. However, the enhanced flexibility of message-based systems comes along with new threats and risks. To face these issues, a variety of security mechanisms and approaches is supported by the Web Service specifications. The usage of these security mechanisms and protocols is configured by stating security requirements in security policies. However, security policy languages for SOA are complex and difficult to create due to the expressiveness of these languages. To facilitate and simplify the creation of security policies, this thesis presents a model-driven approach that enables the generation of complex security policies on the basis of simple security intentions. SOA architects can specify these intentions in system design models and are not required to deal with complex technical security concepts. The approach introduced in this thesis enables the enhancement of any system design modelling languages - for example FMC or BPMN - with security modelling elements. The syntax, semantics, and notion of these elements is defined by our security modelling language SecureSOA. The metamodel of this language provides extension points to enable the integration into system design modelling languages. In particular, this thesis demonstrates the enhancement of FMC block diagrams with SecureSOA. To enable the model-driven generation of security policies, a domain-independent policy model is introduced in this thesis. This model provides an abstraction layer for security policies. Mappings are used to perform the transformation from our model to security policy languages. However, expert knowledge is required to generate instances of this model on the basis of simple security intentions. Appropriate security mechanisms, protocols and options must be chosen and combined to fulfil these security intentions. In this thesis, a formalised system of security patterns is used to represent this knowledge and to enable an automated transformation process. Moreover, a domain-specific language is introduced to state security patterns in an accessible way. On the basis of this language, a system of security configuration patterns is provided to transform security intentions related to data protection and identity management. The formal semantics of the security pattern language enable the verification of the transformation process introduced in this thesis and prove the correctness of the pattern application. Finally, our SOA Security LAB is presented that demonstrates the application of our model-driven approach to facilitate a dynamic creation, configuration, and execution of secure Web Service-based composed applications.},
  language  = {en}
}
@misc{KliemeTietzMeinel2018,
  author    = {Klieme, Eric and Tietz, Christian and Meinel, Christoph},
  title     = {Beware of SMOMBIES},
  series = {The 17th IEEE International Conference on Trust, Security and Privacy in Computing and Communications (IEEE TrustCom 2018)/the 12th IEEE International Conference on Big Data Science and Engineering (IEEE BigDataSE 2018)},
  journal   = {The 17th IEEE International Conference on Trust, Security and Privacy in Computing and Communications (IEEE TrustCom 2018)/the 12th IEEE International Conference on Big Data Science and Engineering (IEEE BigDataSE 2018)},
  publisher = {IEEE},
  address   = {New York},
  isbn      = {978-1-5386-4387-7},
  issn      = {2324-9013},
  doi       = {10.1109/TrustCom/BigDataSE.2018.00096},
  pages     = {651 -- 660},
  year      = {2018},
  abstract  = {Several research evaluated the user's style of walking for the verification of a claimed identity and showed high authentication accuracies in many settings. In this paper we present a system that successfully verifies a user's identity based on many real world smartphone placements and yet not regarded interactions while walking. Our contribution is the distinction of all considered activities into three distinct subsets and a specific one-class Support Vector Machine per subset. Using sensor data of 30 participants collected in a semi-supervised study approach, we prove that unsupervised verification is possible with very low false-acceptance and false-rejection rates. We furthermore show that these subsets can be distinguished with a high accuracy and demonstrate that this system can be deployed on off-the-shelf smartphones.},
  language  = {en}
}
@article{ThienenNoweskiMeineletal.2012,
  author    = {Thienen, Julia von and Noweski, Christine and Meinel, Christoph and Lang, Sabine and Nicolai, Claudia and Bartz, Andreas},
  title     = {What can design thinking learn from behavior group theraphy?},
  isbn      = {978-3-642-31990-7},
  year      = {2012},
  language  = {en}
}
@misc{MeinelSack2004,
  author    = {Meinel, Christoph and Sack, Harald},
  title     = {WWW : Kommunikation, Internetworking, Web-Technologien},
  publisher = {Springer},
  address   = {Berlin},
  isbn      = {3-540-44276-6},
  issn      = {1439-5428},
  pages     = {1179 S.},
  year      = {2004},
  language  = {de}
}
@book{MeinelSack2009,
  author    = {Meinel, Christoph and Sack, Harald},
  title     = {Digitale Kommunikation : Vernetzen, Multimedia, Sicherheit},
  series = {Media Press},
  journal   = {Media Press},
  publisher = {Springer-Verlag Berlin Heidelberg},
  address   = {Berlin, Heidelberg},
  isbn      = {978-3-540-92922-2},
  issn      = {1439-3107},
  doi       = {10.1007/978-3-540-92923-9},
  pages     = {422 S.},
  year      = {2009},
  language  = {de}
}
@misc{AlhosseiniAlmodarresiYasinBinTareafNajafietal.2019,
  author    = {Alhosseini Almodarresi Yasin, Seyed Ali and Bin Tareaf, Raad and Najafi, Pejman and Meinel, Christoph},
  title     = {Detect me if you can},
  series = {Companion Proceedings of The 2019 World Wide Web Conference},
  journal   = {Companion Proceedings of The 2019 World Wide Web Conference},
  publisher = {Association for Computing Machinery},
  address   = {New York},
  isbn      = {978-1-4503-6675-5},
  doi       = {10.1145/3308560.3316504},
  pages     = {148 -- 153},
  year      = {2019},
  abstract  = {Spam Bots have become a threat to online social networks with their malicious behavior, posting misinformation messages and influencing online platforms to fulfill their motives. As spam bots have become more advanced over time, creating algorithms to identify bots remains an open challenge. Learning low-dimensional embeddings for nodes in graph structured data has proven to be useful in various domains. In this paper, we propose a model based on graph convolutional neural networks (GCNN) for spam bot detection. Our hypothesis is that to better detect spam bots, in addition to defining a features set, the social graph must also be taken into consideration. GCNNs are able to leverage both the features of a node and aggregate the features of a node's neighborhood. We compare our approach, with two methods that work solely on a features set and on the structure of the graph. To our knowledge, this work is the first attempt of using graph convolutional neural networks in spam bot detection.},
  language  = {en}
}
@article{LindbergMeinelWagner2011,
  author    = {Lindberg, Tilmann and Meinel, Christoph and Wagner, Ralf},
  title     = {Design thinking : a fruitful concept for IT development?},
  isbn      = {978-3-642-13756-3},
  year      = {2011},
  language  = {en}
}
@article{MeinelKlotz2006,
  author    = {Meinel, Christoph and Klotz, Volker},
  title     = {The first 10 years of the ECCC digital library},
  doi       = {10.1145/1107458.1107484},
  year      = {2006},
  language  = {en}
}
@article{GruenewaldMeinel2015,
  author    = {Gr{\"u}newald, Franka and Meinel, Christoph},
  title     = {Implementation and Evaluation of Digital E-Lecture Annotation in Learning Groups to Foster Active Learning},
  series = {IEEE transactions on learning technologies},
  volume    = {8},
  journal   = {IEEE transactions on learning technologies},
  number    = {3},
  publisher = {Inst. of Electr. and Electronics Engineers},
  address   = {Los Alamitos},
  issn      = {1939-1382},
  doi       = {10.1109/TLT.2015.2396042},
  pages     = {286 -- 298},
  year      = {2015},
  abstract  = {The use of video lectures in distance learning involves the two major problems of searchability and active user participation. In this paper, we promote the implementation and usage of a collaborative educational video annotation functionality to overcome these two challenges. Different use cases and requirements, as well as details of the implementation, are explained. Furthermore, we suggest more improvements to foster a culture of participation and an algorithm for the extraction of semantic data. Finally, evaluations in the form of user tests and questionnaires in a MOOC setting are presented. The results of the evaluation are promising, as they indicate not only that students perceive it as useful, but also that the learning effectiveness increases. The combination of personal lecture video annotations with a semantic topic map was also evaluated positively and will thus be investigated further, as will the implementation in a MOOC context.},
  language  = {en}
}
@phdthesis{Schnjakin2014,
  author    = {Schnjakin, Maxim},
  title     = {Cloud-RAID},
  pages     = {137},
  year      = {2014},
  language  = {de}
}
@phdthesis{Saleh2016,
  author    = {Saleh, Eyad},
  title     = {Securing Multi-tenant SaaS Environments},
  school      = {Universit{\"a}t Potsdam},
  pages     = {108},
  year      = {2016},
  abstract  = {Software-as-a-Service (SaaS) offers several advantages to both service providers and users. Service providers can benefit from the reduction of Total Cost of Ownership (TCO), better scalability, and better resource utilization. On the other hand, users can use the service anywhere and anytime, and minimize upfront investment by following the pay-as-you-go model. Despite the benefits of SaaS, users still have concerns about the security and privacy of their data. Due to the nature of SaaS and the Cloud in general, the data and the computation are beyond the users' control, and hence data security becomes a vital factor in this new paradigm. Furthermore, in multi-tenant SaaS applications, the tenants become more concerned about the confidentiality of their data since several tenants are co-located onto a shared infrastructure. To address those concerns, we start protecting the data from the provisioning process by controlling how tenants are being placed in the infrastructure. We present a resource allocation algorithm designed to minimize the risk of co-resident tenants called SecPlace. It enables the SaaS provider to control the resource (i.e., database instance) allocation process while taking into account the security of tenants as a requirement. Due to the design principles of the multi-tenancy model, tenants follow some degree of sharing on both application and infrastructure levels. Thus, strong security-isolation should be present. Therefore, we develop SignedQuery, a technique that prevents one tenant from accessing others' data. We use the Signing Concept to create a signature that is used to sign the tenant's request, then the server can verifies the signature and recognizes the requesting tenant, and hence ensures that the data to be accessed is belonging to the legitimate tenant. Finally, Data confidentiality remains a critical concern due to the fact that data in the Cloud is out of users' premises, and hence beyond their control. Cryptography is increasingly proposed as a potential approach to address such a challenge. Therefore, we present SecureDB, a system designed to run SQL-based applications over an encrypted database. SecureDB captures the schema design and analyzes it to understand the internal structure of the data (i.e., relationships between the tables and their attributes). Moreover, we determine the appropriate partialhomomorphic encryption scheme for each attribute where computation is possible even when the data is encrypted. To evaluate our work, we conduct extensive experiments with di↵erent settings. The main use case in our work is a popular open source HRM application, called OrangeHRM. The results show that our multi-layered approach is practical, provides enhanced security and isolation among tenants, and have a moderate complexity in terms of processing encrypted data.},
  language  = {en}
}
@article{MeinelWang2006,
  author    = {Meinel, Christoph and Wang, Long},
  title     = {Building content clusters based on modelling page pairs},
  doi       = {10.1007/11610113_85},
  year      = {2006},
  abstract  = {We give a new view on building content clusters from page pair models. We measure the heuristic importance within every two pages by computing the distance of their accessed positions in usage sessions. We also compare our page pair models with the classical pair models used in information theories and natural language processing, and give different evaluation methods to build the reasonable content communities. And we finally interpret the advantages and disadvantages of our models from detailed experiment results},
  language  = {en}
}
@phdthesis{SadrAzodi2015,
  author    = {Sadr-Azodi, Amir Shahab},
  title     = {Towards Real-time SIEM-based Network monitoring and Intrusion Detection through Advanced Event Normalization},
  school      = {Universit{\"a}t Potsdam},
  pages     = {144},
  year      = {2015},
  language  = {en}
}
@phdthesis{Gericke2014,
  author    = {Gericke, Lutz},
  title     = {Tele-Board - Supporting and analyzing creative collaboration in synchronous and asynchronous scenario},
  pages     = {186},
  year      = {2014},
  language  = {en}
}
@article{JobstKoeppenLindbergetal.2012,
  author    = {Jobst, Birgit and K{\"o}ppen, Eva and Lindberg, Tilmann and Moritz, Josephine and Rhinow, Holger and Meinel, Christoph},
  title     = {The faith-factor in design thinking : creative confidence through education at the design thinking schools Potsdam and Standford?},
  isbn      = {978-3-642-31990-7},
  year      = {2012},
  language  = {en}
}
@article{NoweskiScheerBuettneretal.2012,
  author    = {Noweski, Christine and Scheer, Andrea and B{\"u}ttner, Nadja and Thienen, Julia von and Erdmann, Johannes and Meinel, Christoph},
  title     = {Towards a paradigm shift in education practice : developing twenty-first century skills with design thinking},
  isbn      = {978-3-642-31990-7},
  year      = {2012},
  language  = {en}
}
@article{GumiennyGerickeWenzeletal.2012,
  author    = {Gumienny, Raja and Gericke, Lutz and Wenzel, Matthias and Meinel, Christoph},
  title     = {Tele-board in use : applying aq digital whiteboard system in different situations and setups},
  isbn      = {978-3-642-31990-7},
  year      = {2012},
  language  = {en}
}
@article{ThienenNoweskiRauthetal.2012,
  author    = {Thienen, Julia von and Noweski, Christine and Rauth, Ingo and Meinel, Christoph and Lange, Sabine},
  title     = {If you want to know who are, tell me where you are : the importance of places},
  year      = {2012},
  language  = {en}
}
@article{MeinelLeifer2012,
  author    = {Meinel, Christoph and Leifer, Larry},
  title     = {Design thinking research},
  isbn      = {978-3-642-31990-7},
  year      = {2012},
  language  = {en}
}
@book{LinckelsMeinel2011,
  author    = {Linckels, Serge and Meinel, Christoph},
  title     = {E-Librarian service : user-friendly semantic search in digital libraries},
  publisher = {Springer-Verlag Berlin Heidelberg},
  address   = {Berlin, Heidelberg},
  isbn      = {978-3-642-17742-2},
  doi       = {10.1007/978-3-642-17743-9},
  pages     = {212 S.},
  year      = {2011},
  language  = {en}
}
@article{MeinelLeifer2011,
  author    = {Meinel, Christoph and Leifer, Larry},
  title     = {Design thinking research},
  isbn      = {978-3-642-13756-3},
  year      = {2011},
  language  = {en}
}
@misc{OPUS4-33848,
  title     = {Design thinking : understand - improve - apply},
  editor    = {Plattner, Hasso and Meinel, Christoph and Leifer, Larry},
  publisher = {Springer-Verlag Berlin Heidelberg},
  address   = {Berlin, Heidelberg},
  isbn      = {978-3-642-13756-3},
  pages     = {236 S.},
  year      = {2011},
  language  = {en}
}
@article{GumiennyMeinelGerickeetal.2011,
  author    = {Gumienny, Raja and Meinel, Christoph and Gericke, Lutz and Quasthoff, Matthias and LoBue, Peter and Willems, Christian},
  title     = {Tele-board : enabling efficient collaboration in digital design spaces across time and distance},
  isbn      = {978-3-642-13756-3},
  year      = {2011},
  language  = {en}
}
@article{ThienenNoweskiMeineletal.2011,
  author    = {Thienen, Julia von and Noweski, Christine and Meinel, Christoph and Rauth, Ingo},
  title     = {The co-evolution of theory and practice in design thinking - or - "Mind the oddness trap!"},
  isbn      = {978-3-642-13756-3},
  year      = {2011},
  language  = {en}
}
@article{LindbergKoeppenRauthetal.2012,
  author    = {Lindberg, Tilmann and K{\"o}ppen, Eva and Rauth, Ingo and Meinel, Christoph},
  title     = {On the perection, adoption and Implementation of design thinking in the IT industry},
  year      = {2012},
  language  = {en}
}
@article{GerickeGumiennyMeinel2012,
  author    = {Gericke, Lutz and Gumienny, Raja and Meinel, Christoph},
  title     = {Tele-board : folow the traces of your design process history},
  year      = {2012},
  language  = {en}
}
@article{MeinelLeifer2012,
  author    = {Meinel, Christoph and Leifer, Larry},
  title     = {Design thinking research},
  year      = {2012},
  language  = {en}
}
@book{OPUS4-33866,
  title     = {Dsign thinking research : studying co-creation in practice},
  editor    = {Plattner, Hasso and Meinel, Christoph and Leifer, Larry},
  publisher = {Springer Berlin Heidelberg},
  address   = {Berlin, Heidelberg},
  isbn      = {978-3-642-21642-8},
  doi       = {10.1007/978-3-642-21643-5},
  pages     = {277 S.},
  year      = {2012},
  language  = {en}
}
@phdthesis{AlSaffar2016,
  author    = {Al-Saffar, Loay Talib Ahmed},
  title     = {Analysing prerequisites, expectations, apprehensions, and attitudes of university students studying Computer science},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-98437},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xii, 131},
  year      = {2016},
  abstract  = {The main objective of this dissertation is to analyse prerequisites, expectations, apprehensions, and attitudes of students studying computer science, who are willing to gain a bachelor degree. The research will also investigate in the students' learning style according to the Felder-Silverman model. These investigations fall in the attempt to make an impact on reducing the "dropout"/shrinkage rate among students, and to suggest a better learning environment. The first investigation starts with a survey that has been made at the computer science department at the University of Baghdad to investigate the attitudes of computer science students in an environment dominated by women, showing the differences in attitudes between male and female students in different study years. Students are accepted to university studies via a centrally controlled admission procedure depending mainly on their final score at school. This leads to a high percentage of students studying subjects they do not want. Our analysis shows that 75\% of the female students do not regret studying computer science although it was not their first choice. And according to statistics over previous years, women manage to succeed in their study and often graduate on top of their class. We finish with a comparison of attitudes between the freshman students of two different cultures and two different university enrolment procedures (University of Baghdad, in Iraq, and the University of Potsdam, in Germany) both with opposite gender majority. The second step of investigation took place at the department of computer science at the University of Potsdam in Germany and analyzes the learning styles of students studying the three major fields of study offered by the department (computer science, business informatics, and computer science teaching). Investigating the differences in learning styles between the students of those study fields who usually take some joint courses is important to be aware of which changes are necessary to be adopted in the teaching methods to address those different students. It was a two stage study using two questionnaires; the main one is based on the Index of Learning Styles Questionnaire of B. A. Solomon and R. M. Felder, and the second questionnaire was an investigation on the students' attitudes towards the findings of their personal first questionnaire. Our analysis shows differences in the preferences of learning style between male and female students of the different study fields, as well as differences between students with the different specialties (computer science, business informatics, and computer science teaching). The third investigation looks closely into the difficulties, issues, apprehensions and expectations of freshman students studying computer science. The study took place at the computer science department at the University of Potsdam with a volunteer sample of students. The goal is to determine and discuss the difficulties and issues that they are facing in their study that may lead them to think in dropping-out, changing the study field, or changing the university. The research continued with the same sample of students (with business informatics students being the majority) through more than three semesters. Difficulties and issues during the study were documented, as well as students' attitudes, apprehensions, and expectations. Some of the professors and lecturers opinions and solutions to some students' problems were also documented. Many participants had apprehensions and difficulties, especially towards informatics subjects. Some business informatics participants began to think of changing the university, in particular when they reached their third semester, others thought about changing their field of study. Till the end of this research, most of the participants continued in their studies (the study they have started with or the new study they have changed to) without leaving the higher education system.},
  language  = {en}
}
@article{Broeker2015,
  author    = {Br{\"o}ker, Kathrin},
  title     = {Unterst{\"u}tzung Informatik-Studierender durch ein Lernzentrum},
  series = {HDI 2014 : Gestalten von {\"U}berg{\"a}ngen},
  volume    = {2015},
  journal   = {HDI 2014 : Gestalten von {\"U}berg{\"a}ngen},
  number    = {9},
  editor    = {Schubert, Sigrid and Schwill, Andreas},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-84754},
  pages     = {189 -- 197},
  year      = {2015},
  abstract  = {In diesem Papier wird das Konzept eines Lernzentrums f{\"u}r die Informatik (LZI) an der Universit{\"a}t Paderborn vorgestellt. Ausgehend von den fachspezifischen Schwierigkeiten der Informatik Studierenden werden die Angebote des LZIs erl{\"a}utert, die sich {\"u}ber die vier Bereiche Individuelle Beratung und Betreuung, „Offener Lernraum", Workshops und Lehrveranstaltungen sowie Forschung erstrecken. Eine erste Evaluation mittels Feedbackb{\"o}gen zeigt, dass das Angebot bei den Studierenden positiv aufgenommen wird. Zuk{\"u}nftig soll das Angebot des LZIs weiter ausgebaut und verbessert werden. Ausgangsbasis dazu sind weitere Studien.},
  language  = {de}
}
@phdthesis{Prasse2016,
  author    = {Prasse, Paul},
  title     = {Pattern recognition for computer security},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-100251},
  school      = {Universit{\"a}t Potsdam},
  pages     = {VI, 75},
  year      = {2016},
  abstract  = {Computer Security deals with the detection and mitigation of threats to computer networks, data, and computing hardware. This thesis addresses the following two computer security problems: email spam campaign and malware detection. Email spam campaigns can easily be generated using popular dissemination tools by specifying simple grammars that serve as message templates. A grammar is disseminated to nodes of a bot net, the nodes create messages by instantiating the grammar at random. Email spam campaigns can encompass huge data volumes and therefore pose a threat to the stability of the infrastructure of email service providers that have to store them. Malware -software that serves a malicious purpose- is affecting web servers, client computers via active content, and client computers through executable files. Without the help of malware detection systems it would be easy for malware creators to collect sensitive information or to infiltrate computers. The detection of threats -such as email-spam messages, phishing messages, or malware- is an adversarial and therefore intrinsically difficult problem. Threats vary greatly and evolve over time. The detection of threats based on manually-designed rules is therefore difficult and requires a constant engineering effort. Machine-learning is a research area that revolves around the analysis of data and the discovery of patterns that describe aspects of the data. Discriminative learning methods extract prediction models from data that are optimized to predict a target attribute as accurately as possible. Machine-learning methods hold the promise of automatically identifying patterns that robustly and accurately detect threats. This thesis focuses on the design and analysis of discriminative learning methods for the two computer-security problems under investigation: email-campaign and malware detection. The first part of this thesis addresses email-campaign detection. We focus on regular expressions as a syntactic framework, because regular expressions are intuitively comprehensible by security engineers and administrators, and they can be applied as a detection mechanism in an extremely efficient manner. In this setting, a prediction model is provided with exemplary messages from an email-spam campaign. The prediction model has to generate a regular expression that reveals the syntactic pattern that underlies the entire campaign, and that a security engineers finds comprehensible and feels confident enough to use the expression to blacklist further messages at the email server. We model this problem as two-stage learning problem with structured input and output spaces which can be solved using standard cutting plane methods. Therefore we develop an appropriate loss function, and derive a decoder for the resulting optimization problem. The second part of this thesis deals with the problem of predicting whether a given JavaScript or PHP file is malicious or benign. Recent malware analysis techniques use static or dynamic features, or both. In fully dynamic analysis, the software or script is executed and observed for malicious behavior in a sandbox environment. By contrast, static analysis is based on features that can be extracted directly from the program file. In order to bypass static detection mechanisms, code obfuscation techniques are used to spread a malicious program file in many different syntactic variants. Deobfuscating the code before applying a static classifier can be subjected to mostly static code analysis and can overcome the problem of obfuscated malicious code, but on the other hand increases the computational costs of malware detection by an order of magnitude. In this thesis we present a cascaded architecture in which a classifier first performs a static analysis of the original code and -based on the outcome of this first classification step- the code may be deobfuscated and classified again. We explore several types of features including token \$n\$-grams, orthogonal sparse bigrams, subroutine-hashings, and syntax-tree features and study the robustness of detection methods and feature types against the evolution of malware over time. The developed tool scans very large file collections quickly and accurately. Each model is evaluated on real-world data and compared to reference methods. Our approach of inferring regular expressions to filter emails belonging to an email spam campaigns leads to models with a high true-positive rate at a very low false-positive rate that is an order of magnitude lower than that of a commercial content-based filter. Our presented system -REx-SVMshort- is being used by a commercial email service provider and complements content-based and IP-address based filtering. Our cascaded malware detection system is evaluated on a high-quality data set of almost 400,000 conspicuous PHP files and a collection of more than 1,00,000 JavaScript files. From our case study we can conclude that our system can quickly and accurately process large data collections at a low false-positive rate.},
  language  = {en}
}
@phdthesis{Videla2014,
  author    = {Videla, Santiago},
  title     = {Reasoning on the response of logical signaling networks with answer set programming},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-71890},
  school      = {Universit{\"a}t Potsdam},
  year      = {2014},
  abstract  = {Deciphering the functioning of biological networks is one of the central tasks in systems biology. In particular, signal transduction networks are crucial for the understanding of the cellular response to external and internal perturbations. Importantly, in order to cope with the complexity of these networks, mathematical and computational modeling is required. We propose a computational modeling framework in order to achieve more robust discoveries in the context of logical signaling networks. More precisely, we focus on modeling the response of logical signaling networks by means of automated reasoning using Answer Set Programming (ASP). ASP provides a declarative language for modeling various knowledge representation and reasoning problems. Moreover, available ASP solvers provide several reasoning modes for assessing the multitude of answer sets. Therefore, leveraging its rich modeling language and its highly efficient solving capacities, we use ASP to address three challenging problems in the context of logical signaling networks: learning of (Boolean) logical networks, experimental design, and identification of intervention strategies. Overall, the contribution of this thesis is three-fold. Firstly, we introduce a mathematical framework for characterizing and reasoning on the response of logical signaling networks. Secondly, we contribute to a growing list of successful applications of ASP in systems biology. Thirdly, we present a software providing a complete pipeline for automated reasoning on the response of logical signaling networks.},
  language  = {en}
}
@phdthesis{Haider2013,
  author    = {Haider, Peter},
  title     = {Prediction with Mixture Models},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-69617},
  school      = {Universit{\"a}t Potsdam},
  year      = {2013},
  abstract  = {Learning a model for the relationship between the attributes and the annotated labels of data examples serves two purposes. Firstly, it enables the prediction of the label for examples without annotation. Secondly, the parameters of the model can provide useful insights into the structure of the data. If the data has an inherent partitioned structure, it is natural to mirror this structure in the model. Such mixture models predict by combining the individual predictions generated by the mixture components which correspond to the partitions in the data. Often the partitioned structure is latent, and has to be inferred when learning the mixture model. Directly evaluating the accuracy of the inferred partition structure is, in many cases, impossible because the ground truth cannot be obtained for comparison. However it can be assessed indirectly by measuring the prediction accuracy of the mixture model that arises from it. This thesis addresses the interplay between the improvement of predictive accuracy by uncovering latent cluster structure in data, and further addresses the validation of the estimated structure by measuring the accuracy of the resulting predictive model. In the application of filtering unsolicited emails, the emails in the training set are latently clustered into advertisement campaigns. Uncovering this latent structure allows filtering of future emails with very low false positive rates. In order to model the cluster structure, a Bayesian clustering model for dependent binary features is developed in this thesis. Knowing the clustering of emails into campaigns can also aid in uncovering which emails have been sent on behalf of the same network of captured hosts, so-called botnets. This association of emails to networks is another layer of latent clustering. Uncovering this latent structure allows service providers to further increase the accuracy of email filtering and to effectively defend against distributed denial-of-service attacks. To this end, a discriminative clustering model is derived in this thesis that is based on the graph of observed emails. The partitionings inferred using this model are evaluated through their capacity to predict the campaigns of new emails. Furthermore, when classifying the content of emails, statistical information about the sending server can be valuable. Learning a model that is able to make use of it requires training data that includes server statistics. In order to also use training data where the server statistics are missing, a model that is a mixture over potentially all substitutions thereof is developed. Another application is to predict the navigation behavior of the users of a website. Here, there is no a priori partitioning of the users into clusters, but to understand different usage scenarios and design different layouts for them, imposing a partitioning is necessary. The presented approach simultaneously optimizes the discriminative as well as the predictive power of the clusters. Each model is evaluated on real-world data and compared to baseline methods. The results show that explicitly modeling the assumptions about the latent cluster structure leads to improved predictions compared to the baselines. It is beneficial to incorporate a small number of hyperparameters that can be tuned to yield the best predictions in cases where the prediction accuracy can not be optimized directly.},
  language  = {en}
}
@phdthesis{Dick2016,
  author    = {Dick, Uwe},
  title     = {Discriminative Classification Models for Internet Security},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-102593},
  school      = {Universit{\"a}t Potsdam},
  pages     = {x, 57},
  year      = {2016},
  abstract  = {Services that operate over the Internet are under constant threat of being exposed to fraudulent use. Maintaining good user experience for legitimate users often requires the classification of entities as malicious or legitimate in order to initiate countermeasures. As an example, inbound email spam filters decide for spam or non-spam. They can base their decision on both the content of each email as well as on features that summarize prior emails received from the sending server. In general, discriminative classification methods learn to distinguish positive from negative entities. Each decision for a label may be based on features of the entity and related entities. When labels of related entities have strong interdependencies---as can be assumed e.g. for emails being delivered by the same user---classification decisions should not be made independently and dependencies should be modeled in the decision function. This thesis addresses the formulation of discriminative classification problems that are tailored for the specific demands of the following three Internet security applications. Theoretical and algorithmic solutions are devised to protect an email service against flooding of user inboxes, to mitigate abusive usage of outbound email servers, and to protect web servers against distributed denial of service attacks. In the application of filtering an inbound email stream for unsolicited emails, utilizing features that go beyond each individual email's content can be valuable. Information about each sending mail server can be aggregated over time and may help in identifying unwanted emails. However, while this information will be available to the deployed email filter, some parts of the training data that are compiled by third party providers may not contain this information. The missing features have to be estimated at training time in order to learn a classification model. In this thesis an algorithm is derived that learns a decision function that integrates over a distribution of values for each missing entry. The distribution of missing values is a free parameter that is optimized to learn an optimal decision function. The outbound stream of emails of an email service provider can be separated by the customer IDs that ask for delivery. All emails that are sent by the same ID in the same period of time are related, both in content and in label. Hijacked customer accounts may send batches of unsolicited emails to other email providers, which in turn might blacklist the sender's email servers after detection of incoming spam emails. The risk of being blocked from further delivery depends on the rate of outgoing unwanted emails and the duration of high spam sending rates. An optimization problem is developed that minimizes the expected cost for the email provider by learning a decision function that assigns a limit on the sending rate to customers based on the each customer's email stream. Identifying attacking IPs during HTTP-level DDoS attacks allows to block those IPs from further accessing the web servers. DDoS attacks are usually carried out by infected clients that are members of the same botnet and show similar traffic patterns. HTTP-level attacks aim at exhausting one or more resources of the web server infrastructure, such as CPU time. If the joint set of attackers cannot increase resource usage close to the maximum capacity, no effect will be experienced by legitimate users of hosted web sites. However, if the additional load raises the computational burden towards the critical range, user experience will degrade until service may be unavailable altogether. As the loss of missing one attacker depends on block decisions for other attackers---if most other attackers are detected, not blocking one client will likely not be harmful---a structured output model has to be learned. In this thesis an algorithm is developed that learns a structured prediction decoder that searches the space of label assignments, guided by a policy. Each model is evaluated on real-world data and is compared to reference methods. The results show that modeling each classification problem according to the specific demands of the task improves performance over solutions that do not consider the constraints inherent to an application.},
  language  = {en}
}
@phdthesis{AlAreqi2017,
  author    = {Al-Areqi, Samih Taha Mohammed},
  title     = {Semantics-based automatic geospatial service composition},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-402616},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xvi, 163},
  year      = {2017},
  abstract  = {Although it has become common practice to build applications based on the reuse of existing components or services, technical complexity and semantic challenges constitute barriers to ensuring a successful and wide reuse of components and services. In the geospatial application domain, the barriers are self-evident due to heterogeneous geographic data, a lack of interoperability and complex analysis processes. Constructing workflows manually and discovering proper services and data that match user intents and preferences is difficult and time-consuming especially for users who are not trained in software development. Furthermore, considering the multi-objective nature of environmental modeling for the assessment of climate change impacts and the various types of geospatial data (e.g., formats, scales, and georeferencing systems) increases the complexity challenges. Automatic service composition approaches that provide semantics-based assistance in the process of workflow design have proven to be a solution to overcome these challenges and have become a frequent demand especially by end users who are not IT experts. In this light, the major contributions of this thesis are: (i) Simplification of service reuse and workflow design of applications for climate impact analysis by following the eXtreme Model-Driven Development (XMDD) paradigm. (ii) Design of a semantic domain model for climate impact analysis applications that comprises specifically designed services, ontologies that provide domain-specific vocabulary for referring to types and services, and the input/output annotation of the services using the terms defined in the ontologies. (iii) Application of a constraint-driven method for the automatic composition of workflows for analyzing the impacts of sea-level rise. The application scenario demonstrates the impact of domain modeling decisions on the results and the performance of the synthesis algorithm.},
  language  = {en}
}