Try to produce query containing union.

translates the `query` to the appropriate query language note: **must** be overriden by subclasses

Return union graph pattern. Returned object can be used as argument in :meth:`Query.where` method. union()` accepts multiple arguments,

returns a `class object` from the supplied `uri`. A valid class name is retrieved using the :func:`uri_to_classname` method. .. code-blo