We could use a general language itself to model structure Structural definition within a programming language isnt good for storing numerous pieces of small data but is very good at defining complex relationships and behavior whilst still providing a consistant interface/ protocol. Modelling using custom created formats can be limiting but tools such as python are designed with general purpose in mind and can adapt well to many situations.
A common interface may be needed or a way to emulate my minds ability to dynamically locate interface points.
How we may go about informing programmatic system components of custom written code can be discussed here: Implementation of user specified code
To use an example, if we wanted to model the production of potatos then we could describe this using a python class or set of functions.