Please help newbie on group definition for own custom yum repositories

[Robinson Tiemuqinke]

Hi,

 Newbie questions regarding group definition for own
custom yum repositories for installatino and upgrade
systems.

 I have created my own package repositories for FC4
and FC5, and created metadata files with createrepo
command. Then I could install individual pacakges
without problems.

 But my question is: How I can define my own group(s)
like redhat did? do I have to write a similar xml
file? if so then where can I find a document for this
task?

 If I create a group definition file, which commands I
have to run to put it into functioning?

 At last, How can I change redhat's group XML file? I
don't like its idea of "base", "mandate", "optional
and default on", "optional and default off", this make
it interactive-friendly but largescale-terrible. 

I like a idea of "either in group and always on, or
just not in this group", so that it will be much
easier for central non-interactive installation and
distribution upgrade. If my idea reasonable? 

Please help this newbie. Thanks a lot.
  

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