Is SR Partner is a Contact(AP) or Customer(KU)?

Hi,

Currently we are working on SAP R/3 3.1i version and we are migrating to ECC6.0. For regulatory reasons we have to implement EH&S and has to automate MSDS Printing. In 3.1i we defined the SR Partner as Contact (AP). But Some says that this should be defined as Customer (KU). Can any one tell us what is the standard setting around SR partner and what is the use and How to create SR Partners and where to assign

Appreciate your quick reply on this

Regards,

Pradeep