RDF generally follows the open-world assumption: information is incomplete by default. Consequently, SPARQL queries cannot retrieve with certainty complete answers, and even worse, when they involve negation, it is unclear whether they produce sound answers. Nevertheless, there is hope to lift thislimitation. On many specific topics (e.g., children of Trump, Apollo 11 crew, EU founders), RDF data sources contain complete information, a fact that can be made explicit through completeness statements. In this work, we leverage completeness statements over RDF data sources to provide guarantees of completeness and soundness for conjunctive SPARQL queries. We develop a technique to check whether query completeness can be guaranteed by taking into account also the specifics of the queried graph, and analyze the complexity of such checking. For queries with negation, we approach the problem of query soundness checking, and distinguish between answer soundness (i.e., is an answer of a query sound?) and pattern soundness (i.e., is a query as a whole sound?). We provide a formalization and characterize the soundness problem via a reduction to the completeness problem. We further develop heuristic techniques for completeness checking, and conduct experimental evaluations based on Wikidata, a prominent, real-world knowledge base, to demonstrate the feasibility of our approach.

中文翻译：

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具有完整性声明的RDF数据源上的SPARQL联合查询的完整性和完整性保证

RDF通常遵循开放世界的假设：默认情况下信息不完整。因此，SPARQL查询无法确定地获取完整答案，甚至更糟的是，当它们涉及否定时，还不清楚它们是否产生合理的答案。尽管如此，仍然有希望解除这一限制。在许多特定主题上（例如，特朗普的孩子，阿波罗11号船员的孩子，欧盟创始人），RDF数据源包含完整的信息，这一事实可以通过完整性声明予以明确。在这项工作中，我们利用RDF数据源上的完整性声明为联合SPARQL查询提供完整性和健全性的保证。我们开发了一种技术，可以通过同时考虑查询图的细节来检查是否可以保证查询的完整性，并分析这种检查的复杂性。对于带有否定的查询，我们处理查询健全性检查的问题，并区分答案健全性（即查询声音的答案？）和模式健全性（即查询作为整体声音吗？）。我们提供形式化并通过简化完整性问题来表征健全性问题。我们进一步开发用于完整性检查的启发式技术，并基于Wikidata（一个著名的现实世界知识库）进行实验评估，以证明我们的方法的可行性。