attribute on species and compartments introduced?
If a model does not contain algebraic rules, it is possible to infer which components (species, compartment and parameters) are meant to change in value by examining the set of scalar rules, rate rules, and reactions. However, if a model contains algebraic rules, you need information about which symbols are meant to be variables and which constants, to solve the system of equations. The mere occurence of a symbol in an algebraic rule doesn’t imply that the symbol is a variable. OK, you ask, but why have a constant flag on species? Why not define constant species as parameters instead? Well, if you define something as a parameter, you lose information about the nature of that symbol: a parameter has nothing on it that says whether it is meant to be the amount of a species, or a volume of a compartment, or a numeric constant of any other kind. However, such semantic information may be useful in a model—it may be useful for a model interpreter to be able to determine that a particular sym
