Experimenting.. intermediate state
Variables moved from <entity> to <instance_generator>, and storing GeneratedValue (the URI) instead of the created resources.
Paying attention to X3ML version number.
DomainContext XPath syntax trick removed.  Now if there is == in the path/source_relation it is treated as a relational model, it is assumed to be <source-fk> == <path-pk>.
Also, XPathInput is being clever by caching a map for (range pk -> range node) and subsequently doing lookups in it.
In relational XML where == is used, the range/source_node is from the root.
In hierarchical XML where == is not used, the XPath expressions extend each other domain-path-range,
except for the case where path/source_relation and range/source_node are identical.
Experiment encoding URI policy
Experiment encoding URI policy- correction