It depends on how your attribute is defined: literal, $p (parameter) or $f (function).
There’s no way to download collection from the attribute, instead of string.
However there is a possibility to read it as String, BigDecimal, boolean, Date, Integer, double.
If $p (cascade get) : will get ParamValue, it’s a parameter result matrix. We can read every column and line. If any column is defined as array (in GUI: checkbox TAB), then that cell may be read as array.
If $f (cascade call): object we’ll get can be any kind, it depends only on the linked function.