As far as we know, in SPARQL query processing, the FROM clause is used to identify the default graph for a query and if multiple FROM clauses are specified in a query then the contents of those graphs are merged to provide a union graph. Having said that, our questions are:
If multiple FROM NAMED clauses are specified in a query then the contents of those graphs are not merged to provide a union graph, right?
If yes, is there any trick or workaround to specify multiple FROM NAMED clauses in a query to execute the query over the union of all named graphs while returning the graph name as a variable too?
Is it possible to create a virtual graph which is a union of two or more named graphs?