Communicating models

The ODD protocol

The ODD protocol (Grimm et al 2006) has been designed for individual based models, but it can be adapted to other kinds of models. It has been recently reviewed by Grimm et al. 2010. The basic idea of the protocol is to structure the information about an IBM in the same sequence. The sequence consists of seven elements that can be grouped in three blocks. The ODD web page with forum discussion can be found at: http://www.ufz.de/oesatools/odd.

Overview

The overview consists of three elements which provide an overview of the overall purpose and structure of the model.

• • Purpose: The purpose of a model has to be stated first because without knowing it readers cannot understand why some aspects of reality are included while others are ignored.

  • Entities, state variables and scales: What kinds of entities are in the model? By what state variables, or attributes, are these entities characterized? What are the temporal and spatial resolutions and extents of the model? The full set of state variables should be described. It is important not to confuse low-level state variables with auxiliary, or aggregated, variables. Types of entities are:

    • Agents/individuals

    • Spatial units

    • Environment

    • Collectives

  • Process overview and scheduling: To understand a model we must know which processes are built into the model. Conceptual, verbal, description of each process and its effects is sufficient here. The scheduling of the model should be described (the order of processes and the order in which state variables are updated).

Design concepts

The design concepts provide a common framework for designing and communiticating IBMs. The sequence of checklist items to be followed when describing (and designing) models will depend on the kind of model being described.

Details

Here implementation details are given:

• • Initialization: This deals with how state variables are initialized at the start of a simulation run (variability among runs, where data came from...)

  • Input: Input variables may change over space and time. All these impose dynamics of certain state variables.

  • Submodels: All submodels representing the processes listed above should be presented and explained. Two versions of the detailed model description should be written:

    • The mathematical skeleton of the model

    • A full model description with the same structure as the skeleton.

Bibliography

• • Grimm, V., Berger, U., Bastiansen, F., Eliassen, S., Ginot, V., Giske, J., Goss-Custard, J., Grand, T., Heinz, S.K. & Huse, G. (2006) A standard protocol for describing individual-based and agent-based models. Ecological Modelling, 198, 115-126.

  • Grimm, V., Berger, U., DeAngelis, D. & Polhill, J. (2010) The ODD protocol : a review and first update. Ecological Modelling, 221, 2760-2768.