Philipp Christmann after successfully defending his thesis. Photo: MPI-INF/Bertram Somieski
On Friday, 06 February 2026 Philipp Christmann defended his thesis with the title:"Question Answering over Heterogeneous Sources". From April 2021 until September 2025 he was PhD student in Computer Science at the Saarland Informatics Campus, Saarbrücken and the Max Planck Institute for Informatics under the supervision of Prof. Gerhard Weikum, head of Department "Databases and Information Systems", and Dr. Rishiraj Saha Roy. The doctoral degree is awarded by Saarland University.
Abstract of the thesis:
Question answering (QA) systems provide crisp answers to questions posed by end users. Most existing QA systems rely on a single type of information source for answering: either a curated knowledge base (KB), or a text corpus, or a set of web tables, which limits their answer coverage. This dissertation makes the following salient contributions:
(i) Proposing a general 3-stage architecture for answering questions over heterogeneous sources to improve answer coverage.
(ii) Developing end-to-end QA systems for conversational questions with incomplete intent, temporal questions with implicit or explicit time constraints, and complex questions that involve aggregation, grouping and joining of information from different sources.
(iii) Constructing large-scale benchmarks for conversational, temporal, and complex QA, as well as QA over personal data, which require the integration of heterogeneous sources. By design, answers obtained by our QA systems can be traced back to the underlying evidence, and the approaches build upon small-scale language models for computational efficiency.