Reasoning over Ontologies with Hidden Content: The Import-by-Query Approach

There is currently a growing interest in techniques for hiding parts of the signature of an ontology Kh that is being reused by another ontology Kv. Towards this goal, in this paper we propose the import-by-query framework, which makes the content of Kh accessible through a limited query interface. If Kv reuses the symbols from Kh in a certain restricted way, one can reason over Kv U Kh by accessing only Kv and the query interface. We map out the landscape of the import-by-query problem. In particular, we outline the limitations of our framework and prove that certain restrictions on the expressivity of Kh and the way in which Kv reuses symbols from Kh are strictly necessary to enable reasoning in our setting. We also identify cases in which reasoning is possible and we present suitable import-by-query reasoning algorithms.

💡 Research Summary

The paper introduces the “import‑by‑query” (IBQ) framework as a solution to the problem of reusing ontologies while keeping parts of the source ontology’s signature hidden. Traditional ontology import requires exposing the entire source ontology (Kh) or at least all its axioms, which is undesirable when the owner wishes to protect proprietary or sensitive knowledge. IBQ replaces full exposure with a limited query interface: the consuming ontology (Kv) may only ask well‑defined queries about the shared signature Σₛ, and Kh answers with a set of logical consequences. By combining these answers with its own axioms, Kv can perform reasoning over the union Kv ∪ Kh without ever seeing Kh’s internal axioms.

The authors formally define the problem, specifying the signatures, axioms, and the nature of admissible queries (subsumption, instance checking, entailment). They then explore two orthogonal dimensions of restriction that are essential for the framework to be decidable and tractable. First, the expressivity of Kh must be limited. The paper proves that for expressive description logics such as ALC or more powerful, query‑only access cannot guarantee complete reasoning; instead, logics in the EL, Horn‑DL, or DL‑Lite families are required to keep the query‑entailment problem decidable. Second, the way Kv reuses symbols from Σₛ must be constrained. Simple reuse patterns—where Kv only uses shared concepts in subclass relations or does not embed them in complex expressions—allow safe reasoning. In contrast, complex reuse (e.g., nesting shared concepts inside arbitrary Boolean combinations or role chains) can generate arbitrarily deep inferences that defeat the query‑only approach.

The paper establishes impossibility results showing that without these restrictions, reasoning becomes at least co‑NP‑hard, making any practical algorithm infeasible. Conversely, when Kh is in EL or Horn‑DL and Kv respects “signature‑connectedness” and “cycle‑free” conditions, the authors present polynomial‑time algorithms. The proposed reasoning procedure consists of two phases: (1) Kv performs local reasoning with its own axioms, issuing queries to Kh only when needed; (2) Kh’s query engine returns answer sets, which Kv integrates to verify global consistency. This design can be implemented by extending existing tableau‑based DL reasoners with query calls, requiring minimal changes to current ontology management systems.

Finally, the authors discuss potential applications: privacy‑preserving knowledge sharing in domains such as healthcare and law, modular ontology distribution in cloud services, and dynamic updates where only query interfaces need to be refreshed. By mapping the landscape of what is possible and what is provably impossible, the paper provides both a solid theoretical foundation and practical algorithms for secure, modular ontology reuse.