PRELIMINARY ABSTRACT: --------------------- A Constraint Program For Subgraph Epimorphisms with Application to Identifying Model Reductions in Systems Biology Steven Gay, François Fages, Thierry Martinez and Sylvain Soliman Keywords: Systems biology, Graph morphism, Constraint programming, Graph edition, Model reduction Abstract: This paper presents a constraint program for checking whether one graph can be obtained from another graph by using node deletions and node mergings. This NP-complete problem is equivalent to the existence problem of a subgraph epimorphism between two graphs, This differs from the well-known subgraph isomorphism problem by the existence of merge in addition to delete operations. Subgraph epimorphisms allow us to identify biologically meaningful reduction relationships between biochemical reaction graphs in large model repositories such as biomodels.net. This concept thus offers a computational tool for studying model reductions in systems biology by considering solely the structure of biochemical networks.