This paper develops a methodology for modeling a template of spatial decision support systems (SDSS) using UML and Spatial OCL, a geographic extension to Object Constraint Language, in support to the common agricultural policy. The paper outlines the proposed model for a SDSS, the issues raised during its conception and examples of OCL constraints are given. As presented in the paper, the challenge is to provide a template that could be easily specialized in order to meet the specific needs of different European countries.