API for an e-business portal

We are developing a multipurpose touch screen e-business kiosk, wherein users can access a wide range of services from our third party partner websites ( like search, book & print flight tickets etc) . We need the developer to create an API , which we wanted to provide to our partners so that their services can be made available via our touch screen kiosk. ( Basically the APi should connect our Application with our partners back end ...for example if a user search for flight availablity, the API should pass on necessary values to the partners back end and retrieve the data). Our application is based on j2ee.