Efficient asymmetric inclusion of regular expressions with interleaving and counting for XML type-checking.

The inclusion of Regular Expressions (REs) is the kernel of any type-checking algorithm for XML manipulation languages. XML applications would benefit from the extension of REs with interleaving and counting, but this is not feasible in general, since inclusion is EXPSPACE-complete for such extended REs. In Colazzo et al. (2009) [1] we introduced a notion of “conflict-free REs”, which are extended REs with excellent complexity behaviour, including a polynomial inclusion algorithm  [1] and linear membership (Ghelli et al., 2008  [2]). Conflict-free REs have interleaving and counting, but the complexity is tamed by the “conflict-free” limitations, which have been found to be satisfied by the vast majority of the content models published on the Web.