private OperatorNode<SequenceOperator> readMultiSource(Scope scope, Source_listContext multiSource) {
        List<List<String>> sourceNameList = new ArrayList<>();
        List<Namespaced_nameContext> nameSpaces = multiSource.namespaced_name();
        for(Namespaced_nameContext node : nameSpaces) {
            List<String> name = readName(node);
            sourceNameList.add(name);
        }
        return OperatorNode.create(toLocation(scope, multiSource), SequenceOperator.MULTISOURCE, sourceNameList);
    }
Translate the ANTLR grammar into the logical representation.
container-search/src/main/java/com/yahoo/search/yql/ProgramParser.java