This document contains reference material for the XMM SAS Data Access Layer (DAL) software.
The DAL's Application Programmable Interface (API) supports four languages; F90, C++, C and Perl.
Primarily, this document will serve as reference material for the F90 DAL API. The C++ and C APIs are also described but with less detail.
Where appropriate, a language-independent approach has been taken and this will partially serve as general user information.
It is a mandatory requirement that all SAS task developers must use the DAL APIs to access FITS files.