google 'application interface requirements template'
samples
Interface Requirements Document faaco.faa.gov
Application architecture detail template - interface control document dpi.state.nc.us
standard practice
Preparation of Web Service Requirements Documents faa.gov
FAA-STD-025f: Preparation of Interface Documentation
http://ato-p.se-apps.faa.gov/faastandards/
this link is 404; the standard is available from everyspec.com:
FAA-STD-025f: Preparation of Interface Documentation everyspec.com