Research & Interests

Recent Independent Work

2026
The decidability of ALCI_RCC5:
Whether concept satisfiability in ALCI_RCC5 - the description logic ALCI with the RCC5 spatial relations as roles - is decidable has been open since I stated the problem in 2002/2003. In 2026, I directed a sustained, adversarially reviewed attack on it by AI assistants. The full question is still open. One sub-question is settled: for the ∀PO-free fragment there is now a decision procedure that is checked in Lean 4.
Overview paper, paper on the decidable fragment. Neither is peer-reviewed.
2026
SHACL, nRQL, and property graphs - what came first?
A semantic and historical comparison of SHACL validation (2017) with what RacerPro's nRQL and its data substrate could already express in 2005. The reports were drafted by generative AI systems at my initiative and checked against the cited publications and the RacerPro manuals. Main report.
2026
My PhD thesis in English:
The thesis is 586 pages long and in German. There is now an extended English summary, written by Claude Code, that connects it to the systems it describes - Racer and nRQL, MiDeLoRa, and DLMAPS - together with an errata list.

Projects at SRI International (2010 - today)

2022 - today
SRI International, Artificial Intelligence Center - Senior Computer Scientist:
PARADIGM: PARACHUTE, a Prolog-based framework for abductive trace completion and projection. It tracks and guides medical procedures in real time, under noisy and incomplete observations, as part of the AMIRA task guidance system in the ARPA-H PARADIGM program. KEPS 2026 paper.
COLLEAGUE: a multi-agent Hierarchical Task Network (HTN) planner for SRI's collaborative robot framework, with partially ordered plans, reasoning about pre- and postconditions, and agent-aware task decomposition.
KMASS: research on large language models for knowledge management in the oil and gas domain, and Concept Vectors, an interpretable topic and user model built from multi-label concept classifiers. Paper on the deployed system.
COBRA: a test and evaluation harness for a federated mission-plan repair system.
Pathway Tools: new search facilities, and a six-fold reduction of the compilation time of the Lisp code base. I also refactored Franz's CLIM, the GUI toolkit Pathway Tools is built on, to the current foreign-function interface of Allegro Common Lisp (def-foreign-call and def-foreign-type in place of defforeign and def-c-type), tested on 64-bit Linux and Apple Silicon. This is now part of Franz's CLIM repository.
2017 - 2022
SRI International, Artificial Intelligence Center - Advanced Computer Scientist:
Procedural knowledge capture from video: an ontology-driven multimedia integration architecture that extracts procedural knowledge from how-to videos, using OWL and SPARQL. This work contributed to a US patent.
MEDIC and CHATPAL: two virtual personal assistants built with OntoVPA - one for Army combat medics, with a domain-specific language for authoring medical dialogue workflows, and a personalized companion for elderly users that learns facts about its user in conversation.
Facade classification: deep neural networks that classify building facades by architectural style, trained in PyTorch and deployed as a REST service.
2010 - 2017
SRI International, Artificial Intelligence Center - Computer Scientist:
OntoVPA: an ontology-based dialogue management system for virtual personal assistants. It uses OWL and RDF for the discourse representation and SPARQL rules for the dialogue dynamics, and was deployed for three commercial customers. See the IWSDS 2017 paper and the Common Lisp framework presented at ELS 2022, with a video of the talk.
AURA / Project Halo: I maintained, modernized and scaled the knowledge representation and reasoning backend of the AURA intelligent biology textbook: standard knowledge base exports (OWL2, TPTP, ASP, SILK, first-order logic) of the knowledge base KB_Bio_101, a new ABox-like representation language, and a new high-performance query language. I also worked on question answering algorithms.
Sunflower: refactoring and optimization of the ontology management layer of the Sunflower reasoner for Flora-2, and a graphical ontology editor.

Earlier Projects: Racer Systems and University (2003 - 2013)

2004 - 2013
Racer Systems GmbH & Co. KG - Co-Founder, Developer, Consultant:
The company behind RacerPro, the commercial offspring of the Racer description logic and OWL reasoner. My main contributions were the query language nRQL, the GUI RacerPorter, MiniLisp, and the OWLlink bindings - see below. From 2010 on, I did this work on the side, in my own time and in agreement with SRI, while being fully employed there. Franz Inc. distributed RacerPro in North America and Asia; the partnership has its own card: Franz Inc. & Racer Systems.
2009 - 10/2010
CASAM:
A project funded by the European Commission, see a stream-based cognitive architecture for multimedia interpretation.
2009 - 2010
PreSInt:
A project funded by the German Research Foundation (DFG), see a cognitive architecture for the interpretation of multimedia streams.
This was a joint effort with the CASAM project above.
2008 - 2010
OWLlink:
Work on the W3C Member Submissions OWLlink. I specified the functional binding and the S-Expression binding in collaboration with the company Derivo, colleagues from the university of Ulm, and DOCOMO Euro Labs.
My Common Lisp open source framework OntoLisp provides the native reference implementation of OWLlink.
2008 - 2009
BOEMIE:
A project funded by the European Commission on semantic multi-media interpretation and ontology bootstrapping. My ontology query language "nRQL" was extended with abductive query answering capabilities to provide the reasoning backbone of the semantic interpretation engine.
2007 - 2009
Consultant for DOCOMO Euro Labs:
DL-based complex ontology-based event recognition for the DOCOMO projects "ContextWatcher" and "IYOUIT".
2007 - 2010
MiniLisp:
A termination-safe scripting and extension language for the RacerPro server.
See this Sudoku solver written in MiniLisp and these slides for an explanation (pages 28 - 32).
2004
A Tangram-playing Lisp Program:
This was implemented in CLIM in Lispworks and demonstrates heuristic spatial search to solve geometric tiling problems. The source code is on Github, and there is a paper from the European Lisp Symposium 2021, with a video of the talk.
2003 - 2010
nRQL (new Racer Query Language):
An influential Description Logic and OWL query language for the RacerPro reasoner. The generic query engine underlying nRQL explored the idea of representation- and application-specific entailment relationships (nowadays called "entailment regimes" in SPARQL), offering expressive means such as classical negation and negation as failure, universal quantification, subqueries, user-defined procedural extensions, etc. Many of these expressive means have been adopted for standards such as SPARQL in the meantime.
 
nRQL was the first practical, fully working description logic "ABox" query engine with a heuristic cost-based query optimizer. The optimizer uses selectivity heuristics for re-ordering of subgoals in conjunctive queries, hence generating effective query evaluation plans by rewriting queries.
 
The optimizer was fully operational and documented in RacerPro in 2004. More details about the optimizer can be found in my thesis, together with a comprehensive evaluation of the effectiveness of the various optimization techniques using the LUBM benchmark. Some of these optimization techniques have been applied to SPARQL by other researchers in the meantime, for example, see this paper by Stocker et al., or this paper by Glimm et al.
 
In 2004, nRQL became the first OWL query engine that could answer the queries from the (nowadays standard) "Lehigh University Benchmark (LUBM)" completely.
 
Here is a (non-exclusive) list of researchers who have used nRQL in their projects: 1, 2, 3, 4, 5
The RacerPro User's Guide of December 2005 documents nRQL as it was then (chapter 6). A recent comparison with SHACL and SPARQL 1.1 looks at which of these features became standards later.
2004 - 2010
RacerPorter (for Racer Systems GmbH):
A GUI / IDE for RacerPro. You can see RacerPorter & RacerPro in this YouTube video published by Franz Inc, which used to be a partner company of Racer Systems GmbH & Co. KG. The source code is on Github.

The systems I built for my theses - DLMAPS, MiDeLoRa, VISCO and GenEd - are on their own page: Thesis Work.