Problem mapping 1 row to multiple rows

Hi experts,

I have an inbound message type like this :

<row>

     <key>KEY</key>

     <field1>FIELD1</field1>

     <field2>FIELD2<field2>

     <field3>FIELD3<field3>

</row>

In my outbound mesage type, I want have multiple rows, one row by field, like this :

<row>

     <champ1>KEY</champ1>

     <champ2>1</champ2>     --> constant = 1

     <champ3>FIELD1</champ3>

</row>

<row>

     <champ1>KEY</champ1>

     <champ2>2</champ2>     --> constant = 1

     <champ3>FIELD2</champ3>

</row>

<row>

     <champ1>KEY</champ1>

     <champ2>3</champ2>     --> constant = 1

     <champ3>FIELD3</champ3>

</row>

How can I do this in message mapping ?

Thanks