Updating the Employee Profile Data Using SAP PI

Dear Experts,

i have a requirement of file to soap where the customer is placing the file in sftp server which needs to be integrated to the successfactors. Here my query is i need to do the lookup in successfactors values. for eg the customer sends the employee profile data where the business phone is not filled at the first time . later it is filled by employee. Now i want to Update the value in successfactors if the value is there i dont want to do any thing . if it is not there i need to update it with out changing the other values . i guess it would be done through the soap lookup. Please suggest me

Regards

Giridhar.