Sound like you need to spend more time in the documentation. Also look at the dstx.ini file (or mercator.ini for older versions).
If you ask the second question, you also need to take the basic mapping class from IBM. You can define elements independantly, however, if your group is to be fixed length, it can't contain variable length objects.
BTW what version are you using? Event Server parameters vary by version.
BocaBurger
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