Imports (or extension mechanism) in config XMLs

[marco-brandizi]

I'm using a number of XML that have slightly different SPARQL queries, each working on different data sets, each returning the same projection of fields. This means the Duke XMLs have a lot in common, for what concerns general parameter and schema properties. It would be really useful to have some <import> element in the XML. At the moment, I'm using an XML template having a placeholder like ${dukeCommon}, which I instantiate from the invoker, but what I'm suggesting would be more practical.