The Intelligent Grid Scheduling Service (ISS) aims at finding an optimally suited computational resource for a given application component. An objective cost model function is used to decide it. It includes information on a parametrization of the components and the machines in a Grid, and on the availability of the clusters. The paper presents a detailed formulation of the environment and outlines the integration of the ISS model into the UNICORE-based VIOLA meta-scheduling Grid middleware. This document is an active collaboration between EPFL, EIA-FR, Forschungszentrum Jülich, Fraunhofer Gesellschaft, University of Dortmund, CETIC, CSCS, and Switch.