public Selector select(String rename, Expression expression) {

        OutputAttribute outputAttribute = new OutputAttribute(rename, expression);
        checkSelection(outputAttribute);
        selectionList.add(outputAttribute);
        return this;
    }
Selector selecting query output stream attributes
modules/siddhi-query-api/src/main/java/io/siddhi/query/api/execution/query/selection/Selector.java