Hi Vinay,
Answers to your query
1) The subgroups are used for the HR entities,by default all HR objects shares one number range 01$$.
But you can define specific number range e.g, for orgunits and risks.
For eg: "01O" for orgunits,"01OF" for risks and "01$$" for the rest,
where the 3rd and 4th characters are "OTYPE" of the particular entity.
2) You do not have to create any default one. The subgroup for which you will maintain the interval will be used depending upon the HR object you will create.
3) Internal Noranges means system specifies automatically generated the no ranges.
External no ranges means user manually defined
4) I am not clear with the question.
Regards,
Silky