The CellML home page: http://www.cellml.org/

Coneference paper on ModelicaXML

http://www.modelica.org/events/Conference2003/papers/h39_Pop.pdf

SBML home page

http://www.sbml.org

Virtual Cellhome page: http://www.nrcam.uchc.edu/login/login.html

Unfortunately, although they claim to have a declarative model-representation language, it is not immediately obvious, when visiting their site, where this is defined.