The regular spanners (characterised by vset-automata) are closed under the algebraic operations of union, join and projection, and have desirable algorithmic properties. The core spanners (introduced by Fagin, Kimelfeld, Reiss, and Vansummeren (PODS 2013, JACM 2015) as a formalisation of the core functionality of the query language AQL used in IBM's SystemT) additionally need string-equality selections and it has been shown by Freydenberger and Holldack (ICDT 2016, Theory of Computing Systems 2018) that this leads to high complexity and even undecidability of the typical problems in static analysis and query evaluation. We propose an alternative approach to core spanners: by incorporating the string-equality selections directly into the regular language that represents the underlying regular spanner (instead of treating it as an algebraic operation on the table extracted by the regular spanner), we obtain a fragment of core spanners that, while having slightly weaker expressive power than the full class of core spanners, arguably still covers the intuitive applications of string-equality selections for information extraction and has much better upper complexity bounds of the typical problems in static analysis and query evaluation.

翻译：正则Spanner（由vset自动机刻画）在并、连接和投影等代数运算下封闭，并具有理想的算法性质。核心Spanner（由Fagin、Kimelfeld、Reiss和Vansummeren（PODS 2013, JACM 2015）提出，作为IBM SystemT中使用的查询语言AQL核心功能的形式化）额外需要字符串相等选择。Freydenberger和Holldack（ICDT 2016, Theory of Computing Systems 2018）已证明这会导致静态分析和查询评估中典型问题的高复杂度甚至不可判定性。我们提出一种核心Spanner的替代方法：通过将字符串相等选择直接整合到表示底层正则Spanner的正则语言中（而非将其视为正则Spanner提取表格上的代数运算），我们获得了核心Spanner的一个片段。该片段虽然比完整核心Spanner类的表达能力稍弱，但依然涵盖了字符串相等选择在信息抽取中的直观应用，并且在静态分析和查询评估的典型问题上具有更优的上界复杂度。