This could be very interesting, too (our query engine now with full JSON support -- using sophisticated set-oriented join and aggregate optimizations):

Separating Key Concerns in Query Processing - Set Orientation, Physical Data Independence, and Parallelism

http://wwwlgis.informatik.uni-kl.de/cms/fileadmin/publicatio...

I've also ported their indexing ideas regarding XML to JSON, such that we can easily index whole paths with typed values as described in the README :-) the indexes itself are also versioned, of course and always updated.

First AST index rewrite rules for the query engine Brackit have also been added (Brackit is regargetable, so other data stores can easily implement a couple of interfaces).