论文标题
FEDQPL：关于RDF数据源异质联合会的逻辑查询计划的语言（扩展版）
FedQPL: A Language for Logical Query Plans over Heterogeneous Federations of RDF Data Sources (Extended Version)
论文作者
论文摘要
当查询无法单独从一个数据源获得的答案和见解时，RDF数据源的联合会提供了巨大的潜力。计划在这样的联邦上执行查询的挑战是，联邦可能在联合会成员提供的数据访问接口的类型方面是异质的。在文献中，这一挑战并没有得到太多关注。本文为未来的方法提供了坚实的正式基础，旨在应对这一挑战。我们的主要概念贡献是代表查询执行计划的正式语言；此外，我们确定了该语言的片段，该片段可用于捕获给定查询不同部分选择相关数据源的结果。作为技术贡献，我们表明该片段比现有的源选择方法所支持的片段更具表现力，这实际上强调了这些方法的固有限制。此外，我们表明源选择问题是NP-HARD，在$σ_2^\ Mathrm {p} $中，我们提供了一组全面的重写规则，可以用作查询优化的基础。
Federations of RDF data sources provide great potential when queried for answers and insights that cannot be obtained from one data source alone. A challenge for planning the execution of queries over such a federation is that the federation may be heterogeneous in terms of the types of data access interfaces provided by the federation members. This challenge has not received much attention in the literature. This paper provides a solid formal foundation for future approaches that aim to address this challenge. Our main conceptual contribution is a formal language for representing query execution plans; additionally, we identify a fragment of this language that can be used to capture the result of selecting relevant data sources for different parts of a given query. As technical contributions, we show that this fragment is more expressive than what is supported by existing source selection approaches, which effectively highlights an inherent limitation of these approaches. Moreover, we show that the source selection problem is NP-hard and in $Σ_2^\mathrm{P}$, and we provide a comprehensive set of rewriting rules that can be used as a basis for query optimization.
