JCR defines an SQL2 interface on top of a hierarchical document store
http://www.h2database.com/jcr/grammar.html
Note it doesnt support recursion, but at least it has support for ISCHILDNODE()/ISDECDENDANTNODE().
LINQ is also interesting mainly because I think it fixes one of the biggest issues with SQL: putting the table/collections first rather than the column/field list.
regards,
Lukas Kahwe Smith
m...@pooteeweet.org