  In this paper, the basic ideal of the Event Space Theory and Analyzing Events
are expatiated on. Then it is suggested that how to set up event base library
in developing application software. Based above the designing principle of
facing methodology. Finally, in order to explain how to apply the Event Space
Theory in developing economic evaluation software, the software of "sewage
treatment CAD" in a national "8th-Five Year Plan Research Project" of PRC is
used as an example. This software concerns economic effectiveness evaluation
for construction projects.
