Posted by The JAACS is the Alumni Association of the three Computer Science Institutes INF, IIUN and DIUF of the Universities of Bern, Neuchâtel, and Fribourg. More information about the association and how to register can be found at .
The JAACS annually awards a prize for the best Bachelor, Master, and Doctoral thesis at the INF, IIUN and DIUF that was defended during the academic year. The winners are selected by the respective institutes and are presented the award at the institute’s end-of-year event.
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PhD
Dr. Manuel Ohrndorf, “A History-based Approach for Model Repair Recommendations in Software Engineering” INF, Bern |
Abstract
Software is an everyday companion in today’s technology society that need to be evolved and maintained over long time periods. To manage the complexity of software projects, it has always been an effort to increase the level of abstraction during software development. Model-Driven Engineering (MDE) has shown to be a suitable method to raise abstraction levels during software development. Models are primary development artifacts in MDE that describe complex software systems from different viewpoints.
In MDE software projects, models are heavily edited through all stages of the development process. During this editing process, the models can become inconsistent due to uncertainties in the software design or various editing mistakes. While most inconsistencies can be tolerated temporarily, they need to be resolved eventually. The resolution of an inconsistency affecting a model’s design is typically a creative process that requires a developer’s expertise. Model repair recommendation tools can guide the developer through this process and propose a ranked list of repairs to resolve the inconsistency. However, such tools will only be accepted in practice if the list of recommendations is plausible and understandable to a developer. Current approaches mainly focus on exhaustive search strategies to generate improved versions of an inconsistent model. Such resolutions might not be understandable to developers, may not reflect the original intentions of an editing process, or just undo former work. Moreover, those tools typically resolve multiple inconsistencies at a time, which might lead to an incomprehensible composition of repair proposals.
This thesis proposes a history-based approach for model repair recommendations. The approach focuses on the detection and complementation of incomplete edit steps, which can be located in the editing history of a model. Edit steps are defined by consistency-preserving edit operations (CPEOs), which formally capture complex and error-prone modifications of a specific modeling language. A recognized incomplete edit step can either be undone or extended to a full execution of a CPEO.
The final inconsistency resolution depends on the developer’s approval. The proposed recommendation approach is fully implemented and supported by our interactive repair tool called ReVision. The tool also includes configuration support to generate CPEOs by a semi-automated process.
The approach is evaluated using histories of real-world models obtained from popular open-source modeling projects hosted in the Eclipse Git repository. Our experimental results confirm our hypothesis that most of the inconsistencies, namely 93.4%, can be resolved by complementing incomplete edits. 92.6% of the generated repair proposals are relevant in the sense that their effect can be observed in the models’ histories. 94.9% of the relevant repair proposals are ranked at the topmost position. Our empirical results show that the presented history-based model recommendation approach allows developers to repair model inconsistencies efficiently and effectively.
Laudatio
Model-based software and systems engineering can only be successful in the long term if it is adequately supported by highly specialized tools, including tools for spotting and resolving inconsistencies. In this respect, Mr. Ohrndorf’s PhD thesis shows a groundbreaking and novel path. Formal guarantees of a fully automated repair approach, as pursued by the majority of existing approaches proposed in the literature, are deliberately abandoned in favor of the goal of generating relevant repair proposals. This objective has been fully achieved, and the experimental results even exceed the expectations formulated at the beginning of the work.
In addition to the technical contributions, which are formally grounded on the theory of graph transformation, the empirical evaluation of the repair approach is particularly noteworthy. Despite the lack of publicly available models that can be used for empirical research, Mr. Ohrndorf managed to extract the version histories of a considerable number of open source modeling projects and prepared them for his evaluation. The experimental results are analyzed with utmost scientific rigor, and the prepared study subjects as well as the experimental setup have the potential to be used as a community benchmark for model repair tools in the future.
The outstanding quality of the work is also manifested in the two central preliminary publications on history-based model repair, which were published at top-tier scientifc publication outlets in software engineering (CORE ranking A*).
Link
urn:nbn:ch:bel-bes-7833
https://ubbern.swisscovery.slsp.ch/permalink/41SLSP_UBE/17e6d97/alma99117481803805511
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Master
Francois-Xavier Wicht ”Blockchain privacy notions using the transaction graph model” INF, Bern |
Abstract
Considerable work explores blockchain privacy notions. Yet, it usually employs entirely different models and notations, complicating potential comparisons. In this work, we use the Transaction Directed Acyclic Graph (TDAG) and extend it to capture blockchain privacy notions (PDAG). We give consistent definitions for untraceability, unlinkability, and confidentiality. Moreover, we specify conditions on a blockchain system to achieve each aforementioned privacy notion. Thus, we can compare the two most prominent privacy-preserving blockchains – Monero and Zcash, in terms of privacy guarantees. Finally, we unify linking heuristics from the literature with our graph notation and review a good portion of research on blockchain privacy.
Laudatio
The MSc thesis of François-Xavier Wicht develops a formal model for defining and analyzing blockchain-based cryptocurrencies. This model builds on a model in previous work for blockchains without privacy. The thesis presents quantitative definitions of untraceability and unlinkability of transactions in this model and compares different blockchain architectures in terms of these notions. In particular, his thesis applies the model to two add-on privacy solutions, Coinjoin and Tornado Cash, and to two privacy-preserving blockchains, namely Monero and Zcash. The PDAG model and security notion are clearly and thoroughly explained. The examples are detailed and interesting. A publication of the work in a leading international venue is forthcoming.
Link
https://crypto.unibe.ch/archive/theses/2022.msc.francois-xavier.wicht.pdf
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Bachelor
Tobias Kohler ”Fast Hexahedral Mesh Extraction from Locally Injective Integer-Grid Maps” INF, Bern |
Abstract
Hexahedral meshes are an important class of volumetric discretizations that are often employed in simulation, e.g. with the Finite-Element method. Integer-Grid Maps as boundary-aligned volume parametrizations of tetrahedral meshes onto a voxel grid have proven to be a valuable approach in the field of hex-meshing as they can induce highly structured hexahedral meshes. The decomposition of the map into multiple cell charts due to the presence of singularities and non-identity transitions between adjacent charts makes the process of extracting a hex-mesh from an IGM nontrivial. Additionally, inverted and degenerate charts in the parametrization may cause inconsistencies that need to be fixed in a postprocessing step. As most current methods work without such defects in the IGM, we present a specialized hex-extraction algorithm that expects all cell charts to have a strictly positive volume and aims to be as fast as possible. To achieve this, we apply common rasterization techniques to efficiently extract the hex-mesh’s geometry and use a specifically designed data structure called propeller to extract its topology.
Laudatio
The Bachelor thesis of Tobias Kohler on fast hexahedral mesh extraction defines the new state of the art by offering strong contributions w.r.t. both theory and practice. The devised specialized algorithms and data structures significantly lower the asymptotic time complexity such that the computational time for typical inputs can be reduced from minutes or even hours to seconds. The unconditionally robust hexahedral mesh extraction algorithm is published as an open source library in C++ and it is expected to become the new de facto standard in research as well as industrial applications.
Link
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