[OAI-implementers] Questions on MARC21

[Yang Zhao]

Question #1:
I encountered a problem when I tried to make a MARC21 XML from a so-called
CASI metadata.

There are such tags in CASI metadata like:
<D700a,D700e,D719a,D729a,D719i,D719b,D729b(001)>,
<D700a,D700e,D719a,D729a,D719i,D719b,D729b(002)>,
<D700a,D700e,D719a,D729a,D719i,D719b,D729b(003)>...

(the number inside parentheses, 001, 002, 003..., indicates the multiple
occurence of the tag.)

I just wonder how to express them in MARC21?

I know one of them can be expressed in a sequential way as the following :

- <datafield ind1="" ind2="" tag="700">
  <subfield code="a">Whiton, J. C.</subfield>
  <subfield code="e" />
  </datafield>
- <datafield ind1="" ind2="" tag="719">
  <subfield code="a">NASA Marshall Space Flight Center</subfield>
  </datafield>
- <datafield ind1="" ind2="" tag="729">
  <subfield code="a" />
  </datafield>
- <datafield ind1="" ind2="" tag="719">
  <subfield code="i">Huntsville, AL United States</subfield>
  <subfield code="b">United States</subfield>
  </datafield>
- <datafield ind1="" ind2="" tag="729">
  <subfield code="b">ND736801</subfield>
  </datafield>

But what if there are more than one sets of the above. How can I indicate
than which fields are together in one group?

Question #2:
I have another question about MARC21. There is a <leader> field in MARC21,
which should have a value of 24 byte, telling some properties of the MARC
record.
Why this field is needed? is there any easy way to make the value of
<leader>?

Appreciate your help.