Abstract

Conjunctive Query (CQ) answering is a primary reasoning task over knowledge bases. However, when considering expressive description logics, query answering can be computationally very expensive; reasoners for CQ answering, although heavily optimized, often sacrifice expressive power of the input ontology or completeness of the computed answers in order to achieve tractability and scalability for the problem. In this work, we present a hybrid query answering architecture that combines various services to provide a CQ answering service for OWL. Specifically, it combines scalable CQ answering services for tractable languages with a CQ answering service for a more expressive language approaching the full OWL 2. If the query can be fully answered by one of the tractable services, then that service is used, to ensure maximum performance. Otherwise, the tractable services are used to compute lower and upper bound approximations. The union of the lower bounds and the intersection of the upper bounds are then compared. If the bounds do not coincide, then the “gap” answers are checked using the “full” service. These techniques led to the development of two new systems: (i) RSAComb, an efficient implementation of a new tractable answering service for RSA (role safety acyclic) (ii) ACQuA, a reference implementation of the proposed hybrid architecture combining RSAComb, PAGOdA, and HermiT to provide a CQ answering service for OWL. Our extensive evaluation shows how the additional computational cost introduced by reasoning over a more expressive language like RSA can still provide a significant improvement compared to relying on a fully-fledged reasoner. Additionally, we show how ACQuA can reliably match the performance of PAGOdA, a state-of-the-art CQ answering system that uses a similar approach, and can significantly improve performance when PAGOdA extensively relies on the underlying fully-fledged reasoner.

中文翻译：

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通过不受限制的 OWL 2 本体进行联合查询应答

 抽象的

联合查询（CQ）回答是基于知识库的主要推理任务。然而，当考虑表达描述逻辑时，查询回答的计算成本可能非常昂贵； CQ 回答的推理机虽然经过了深度优化，但通常会牺牲输入本体的表达能力或计算答案的完整性，以实现问题的易处理性和可扩展性。在这项工作中，我们提出了一种混合查询应答架构，它结合了各种服务，为 OWL 提供 CQ 应答服务。具体来说，它将针对易处理语言的可扩展 CQ 应答服务与针对接近完整 OWL 2 的更具表现力的语言的 CQ 应答服务相结合。如果查询可以由其中一种易处理服务完全应答，则使用该服务，以确保最大限度地提高查询效率。表现。否则，易处理的服务用于计算下限和上限近似值。然后比较下限的并集和上限的交集。如果边界不一致，则使用“完整”服务检查“间隙”答案。这些技术导致了两个新系统的开发：(i) RSAComb，一种针对 RSA（角色安全非循环）的新的易处理应答服务的高效实现 (ii) ACQuA，结合了 RSAComb、PAGOdA 的混合架构的参考实现， HermiT 为 OWL 提供 CQ 应答服务。我们的广泛评估表明，与依赖成熟的推理器相比，通过对 RSA 等更具表现力的语言进行推理所带来的额外计算成本仍然可以提供显着的改进。 此外，我们还展示了 ACQuA 如何能够可靠地匹配 PAGOdA（一种使用类似方法的最先进的 CQ 应答系统）的性能，并且当 PAGOdA 广泛依赖于底层成熟的推理器时，可以显着提高性能。