As part of its expanding Astrophysics program, Fermilab is participating in the Digital Sky Survey (DSS). Fermilab is part of a collaboration involving University of Chicago, Princeton University, and the Institute of Advanced Studies (at Princeton). DSS main results will be a photometric imaging survey and a redshift survey of galaxies and color-selected quasars over π steradians of the Northern Galactic Cap. This paper focuses on our use of Computer Aided Software Engineering (CASE) in specifying the data system for DSS. Extensions to ``standard'' methodologies were necessary to compensate for tool shortcomings and to improve communication amongst the collaboration members. One such important extension was the incorporation of CASE information into the specification document.