Confusion with 2 changeset begin and end method In ODATA DPC_EXT Class

Hi Experts,

for batch batch update,create and delete call i am using two methods

/IWBEP/IF_MGW_CORE_SRV_RUNTIME~CHANGESET_BEGIN

/IWBEP/IF_MGW_CORE_SRV_RUNTIME~CHANGESET_END

/IWBEP/IF_MGW_CORE_SRV_RUNTIME~CHANGESET_BEGIN{

      mf_batch = abap_true.  //  this one is an custom attribute i have created for my DPC_EXT class
       EXIT.

}

/IWBEP/IF_MGW_CORE_SRV_RUNTIME~CHANGESET_END{

         CHECK mf_batch EQ abap_true.
  commit work.
CLEAR mf_batch.

}

first of all i am not getting why we write EXIT in changeset_begin method.

Including this also i am getting other 2 method of different interface in my DPC_EXT

/IWBEP/IF_MGW_APPL_SRV_RUNTIME~CHANGESET_BEGIN

/IWBEP/IF_MGW_APPL_SRV_RUNTIME~CHANGESET_END

So could you please tell me what is the purpose of extra 2 methods?

Regards

Saumya