The Aqwa interface for Excel consists of two main parts:
A dynamic link library called aql32/64.dll
An Excel add-in macro sheet called aql32/64.xla
The dynamic link library (or DLL) is a set of functions written in the FORTRAN language. These functions understand enough about the Aqwa file system to extract information from it. They do all the hard work.
The add-in macro sheet provides a set of spreadsheet functions that use the dynamic link library to access the Aqwa file system. These spreadsheet functions can be used like any other functions in an Excel spreadsheet (or 'worksheet' in Microsoft's terminology). All the functions have names starting with the prefix AQL.