In Druid I don't know of any concept of grouping datasources into a "schema".
But I can think of one or two ways to set up datasources (tables) in a hierarchical manner, e.g.:
• ABC_parent_table (parent_id, parent_attr ...)
• ABC_child_table (parent_id, child_id, child_attr, ...)
which would imply a join between the two ...
Is this along the lines of what you are thinking?