Allow field to be index using SPARQL query result over RDF data
The way fields are defined in solr-engine foe the indexing of documents is becoming more and more complex due to the inherent flexibility of RDF statements that are used to get the values to index.
To simplify the configuration, it might be worth using simply SPARQL query to select the values to be indexed.
This evolution implies quite a change on the configuration file of the solr-engine service and a transparent transition would be preferred (with deprecation of the old version).