A clear distinction is made in JAS-mine between objects with a modelling content, which specify the structure of the simulation, and objects which perform useful but auxiliary tasks, from enumerating categorical variables to building graphical widgets, from creating filters for the collection of agents to computing aggregate statistics to be saved in the output database.

JAS-mine extends the Model-Observer paradigm introduced by the Swarm experience and introduces a new layer in simulation modeling, the Collector.

• The Model deals mainly with specification issues, creating objects, relations between objects, and defining the order of events that take place in the simulation.
• The Collector collects the data and compute the statistics both for use by the simulation objects and for post-mortem analysis of the model outcome, after the simulation has completed.
• The Observer allows the user to inspect the simulation in real time and monitor some pre-defined outcome variables as the simulation unfolds.

This three-layer methodological protocol allows for extensive re-use of code and facilitates model building, debugging and communication.

Moreover, a separation is made between code and data, with all parameters and input tables stored either in an input database or in specific MS Excel files. The regression package provides tools for simulating outcomes from standard regression models (OLS, probit/logit, multinomial probit/logit): in particular, there is no need to specify the variables that enter a regression model, as they are directly read from the data files. This greatly facilitates exploration of the parameter space, testing different econometric specifications, and scenario analysis.