Princples of process (systems) based modeling What books are available that address the fundamental principles all processed based modelers should be aware of?  

Is there a guide, some holy grail of text books for process based simulation models? 

Edit:
Process based, or system models such as those used to simulate ecological/biogeochemical/landscape processes. 
As Naught101 mentioned: "process based modelling" refers to a computational-numerical mode built on a conceptual model that is mostly based on physical laws defined by empirical relationships. As opposed to a purely empirical/statistical model.
I guess the only thing the modeler should know is either the mathematical equation describing the system or the statistical relationship between a predictor and a predictand. You might have "access" to the exact equations or you might need to fit a mathematical model onto empirical observations. Then you need to code these mathematical or statistical relationship into a software (i.e. numerical model).

Fairly general. The devil will be in the details.