  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.
