Can I Submit A Self Service Request from the API

Dear All 

I would like to ask Can I do the Self Service from the Database using the API 

I mean Like any other API , I can define the payroll element from the screen or from the API .

I can define a new employee from the Screen or from the API . 

My question is 

Can I do the Absence request from the database using the API 

or (Custom request SIT like ( business trip request ) from the API , I mean Start the Work Flow Process and Approval from the Back end ( Database using API )