Link Field can be obtained by following the followed steps :
  
1> Open the property window of the selected Text Field.
  
2> Select "Yes" for LinkedField column, which will enable the 
button "Create Link", which was disabled initially.
  
3> Click on "Create Link" button,which will open another window
having a title "Link Field".
  
4> Enter proper Relation name in the provided Text Field.
  
5> Select a table from the combo box having a title "Table1",
and select another table from combo box having a title "Table2".
These are the tables between which the mapping has to be done.
  
6> Now select the comun names of table1 and Table2 between
which the mapping has to be done.
  
7> Click on "Map" button to map the two columns.
  
8> Click on "OK" button to save the changes. On 
clicking "OK" button the user returns to the property window.
  
9> Click on "OK" button of the property window to return back to
the OCM user interface.