business maps/validations/ notDuplicate validation on UI10 field

[Svemar]

Hello,
I am trying to implement the map to prevent saving the product witch already exist for the the vendor. So I want to check that there is no saved product with particular vendor_part_no AND particular Vendor name.
I tried the following map, but it does not allow to save product whit the same the vendor_part_no BUT different vendor.
Could you please guide me?

<map>
<originmodule>
<originname>Products</originname>
</originmodule>
<fields>
<field>
<fieldname>vendor_part_no</fieldname>
<validations>
<validation>
<rule>notDuplicate</rule>
</validation>
</validations>
</field>
<field>
<fieldname>vendor_id</fieldname>
<validations>
<validation>
<rule>notDuplicate</rule>
</validation>
</validations>
</field>
</fields>
</map>