how to judge if a shared member is a descendants of a specified member in business rules

@RELATIVE("YearTotal"

how to judge if a shared member is a descendants of a specified member in business rules? Usually, it's the basic member but not the shared member that was judged in the rule.

the example is as follows:

SET UPDATECALC  OFF;

SET AGGMISSG ON;

fix("CU00","SP200","SP100",&BudYear,"Budget",@RELATIVE("YearTotal",0),

   "I00","P00","CNY",&CurVersion,@share(@relative("YXQC200",0))/*甲公司的共享成员*/)

  "A100201010101020101"

  (  /* 判断甲公司的共享成员是否是XX公司的后代 */

  if(@ISDESC("YXQC200")) 

  /* 主营业务成本  */

  "A100201010101020101"=100;

  endif)

endfix