For example, BPEL4WS (5)-connection between partners

Each partner connection has a WSDL parternerlinktype indicating its characteristics. The myrole/partnerrole attribute of the partner connection specifies how the partner and process of the given parternerlinktype interact. The myrole attribute references the role that the process will assume in parternerlinktype, And the partnerrole specifies the role that the partner will assume.
<Partnerlinks>
<Partnerlink name = "customer"
Partnerlinktype = "lNS: loanpartnerlinktype"
Myrole = "loanservice"/>
<Partnerlink name = "approver"
Partnerlinktype = "lNS: loanapprovallinktype"
Partnerrole = "approver"/>
<Partnerlink name = "assessor"
Partnerlinktype = "lNS: riskassessmentlinktype"
Partnerrole = "assessor"/>
</Partnerlinks>

The partner connection represents the interaction between processes. The partner represents the entity that interacts with itself, as shown below:
<Partner name = "sellershipper"
Xmlns ="Http://schemas.xmlsoap.org/ws/2003/05/partner-link/">
<Partnerlink name = "seller"/>
<Partnerlink name = "shipper"/>
</Partner>

The partner is not required in the process definition. the partner does not need to cover all the partner connections in the process definition. when you define a partner, it must implement the task (the service should be provided) that the role of the partner connection under the corresponding partner should complete ). the definition of a partner cannot overlap. That is to say, a partner connection cannot appear in multiple partners' definitions at the same time.