Researcher profile

Manuel Rigger

Manuel Rigger contributes to research discovery and scholarly infrastructure.

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Published work

4 published item(s)

preprint2026arXiv

CAMAL: Improving Attention Alignment and Faithfulness with Segmentation Masks

Many vision datasets now provide segmentation masks in addition to annotated images to support a wide range of tasks. In this work, we propose Class Activation Map Attention Learning (CAMAL), an efficient and scalable method that utilizes segmentation masks to improve attention alignment and faithfulness in vision models. Specifically, attention alignment refers to the degree to which a model's attention aligns with ground-truth discriminative regions, while attention faithfulness refers to the degree to which a model's attention influences its decision. Improving both attention alignment and faithfulness is essential for ensuring that model attention is both spatially accurate and causally meaningful. To improve attention alignment and faithfulness in vision models, CAMAL first extracts the model's attention for each image during training and then compares the attention to ground-truth discriminative regions obtained from the corresponding segmentation masks. CAMAL then acts as an auxiliary regularizer, encouraging attention that aligns with ground-truth discriminative regions, while suppressing attention elsewhere. We evaluated CAMAL across two learning paradigms -- Deep Learning (DL) and Deep Reinforcement Learning (DRL) -- and observed consistent, significant improvements in both attention alignment and faithfulness. In particular, CAMAL yields statistically significant gains in attention alignment across all settings, and improves attention faithfulness by over 35% compared to recent work. Moreover, we show that improved attention alignment and faithfulness enhance explainability, while yielding improved or comparable generalization performance without increasing inference cost. These findings demonstrate that the spatial information contained within segmentation masks can be effectively leveraged to guide model attention across learning tasks.

preprint2023arXiv

Testing Database Engines via Query Plan Guidance

Database systems are widely used to store and query data. Test oracles have been proposed to find logic bugs in such systems, that is, bugs that cause the database system to compute an incorrect result. To realize a fully automated testing approach, such test oracles are paired with a test case generation technique; a test case refers to a database state and a query on which the test oracle can be applied. In this work, we propose the concept of Query Plan Guidance (QPG) for guiding automated testing towards "interesting" test cases. SQL and other query languages are declarative. Thus, to execute a query, the database system translates every operator in the source language to one of potentially many so-called physical operators that can be executed; the tree of physical operators is referred to as the query plan. Our intuition is that by steering testing towards exploring diverse query plans, we also explore more interesting behaviors-some of which are potentially incorrect. To this end, we propose a mutation technique that gradually applies promising mutations to the database state, causing the DBMS to create diverse query plans for subsequent queries. We applied our method to three mature, widely-used, and extensively-tested database systems-SQLite, TiDB, and CockroachDB-and found 53 unique, previously unknown bugs. Our method exercises 4.85-408.48X more unique query plans than a naive random generation method and 7.46X more than a code coverage guidance method. Since most database systems-including commercial ones-expose query plans to the user, we consider QPG a generally applicable, black-box approach and believe that the core idea could also be applied in other contexts (e.g., to measure the quality of a test suite).

preprint2020arXiv

Detecting Optimization Bugs in Database Engines via Non-Optimizing Reference Engine Construction

Database Management Systems (DBMS) are used ubiquitously. To efficiently access data, they apply sophisticated optimizations. Incorrect optimizations can result in logic bugs, which cause a query to compute an incorrect result set. We propose Non-Optimizing Reference Engine Construction (NoREC), a fully-automatic approach to detect optimization bugs in DBMS. Conceptually, this approach aims to evaluate a query by an optimizing and a non-optimizing version of a DBMS, to then detect differences in their returned result set, which would indicate a bug in the DBMS. Obtaining a non-optimizing version of a DBMS is challenging, because DBMS typically provide limited control over optimizations. Our core insight is that a given, potentially randomly-generated optimized query can be rewritten to one that the DBMS cannot optimize. Evaluating this unoptimized query effectively corresponds to a non-optimizing reference engine executing the original query. We evaluated NoREC in an extensive testing campaign on four widely-used DBMS, namely PostgreSQL, MariaDB, SQLite, and CockroachDB. We found 159 previously unknown bugs in the latest versions of these systems, 141 of which have been fixed by the developers. Of these, 51 were optimization bugs, while the remaining were error and crash bugs. Our results suggest that NoREC is effective, general and requires little implementation effort, which makes the technique widely applicable in practice.

preprint2020arXiv

Testing Database Engines via Pivoted Query Synthesis

Relational databases are used ubiquitously. They are managed by database management systems (DBMS), which allow inserting, modifying, and querying data using a domain-specific language called Structured Query Language (SQL). Popular DBMS have been extensively tested by fuzzers, which have been successful in finding crash bugs. However, approaches to finding logic bugs, such as when a DBMS computes an incorrect result set, have remained mostly untackled. Differential testing is an effective technique to test systems that support a common language by comparing the outputs of these systems. However, this technique is ineffective for DBMS, because each DBMS typically supports its own SQL dialect. To this end, we devised a novel and general approach that we have termed Pivoted Query Synthesis. The core idea of this approach is to automatically generate queries for which we ensure that they fetch a specific, randomly selected row, called the pivot row. If the DBMS fails to fetch the pivot row, the likely cause is a bug in the DBMS. We tested our approach on three widely-used and mature DBMS, namely SQLite, MySQL, and PostgreSQL. In total, we reported 123 bugs in these DBMS, 99 of which have been fixed or verified, demonstrating that the approach is highly effective and general. We expect that the wide applicability and simplicity of our approach will enable the improvement of robustness of many DBMS.