Mapping requirement

Hi All,

i need to create segment ReleaseRefNum(occurance  0 to unbounded) based on some condition,under this segment one field availablr RefnoValue

(occurance 1:1)  andatory field

Target Structure

ReleaseRefNum(0:unbounded)

   Ref (0:1)

     ReleaseGid(0:1)

              gid(1:1)

                    DomainName(0:1)

                    Xid  (1:1)

  RefnoValue (occ 1:1)

i am passing constant  value to XId Field   Constant-------->Xid

Tlccat  (Source field) Equals 28 then i need to pass same constant=po  to RefnoValue

if this condition  failed then no need to create  segment

ReleaseRefNum(0:unbounded)

Please  send me the logic .

Thanks,

Aadi