Who (i.e., what entity) does what, and in what order? When are state variables updated? How is time modeled, as discrete steps or as a continuum over which both continuous processes and discrete events can occur? Except for very simple schedules, one should use pseudocode to describe the schedule in every detail, so that the model can be re-implemented from this code. Ideally, the pseudo-code corresponds fully to the actual code used in the program implementing the ABM.

        The “does what?” In the first question refers to the model’s processes. In this ODD element only the self-explanatory names of the model’s processes should be listed: ‘up-date habitat’, ‘move’, ‘grow’, ‘buy’, ‘update plots’, etc. These names are then the titles of the sub-models that are described in the last ODD element, ‘Submodels’. Processes are performed either by one of the model’s entities (for example: ‘move’), or by a higher-level controller that does things such as updating plots or writing output to files. To handle such higher-level processes,  ABM  software  platforms  like  Swarm  (Minar  et  al.,  1996)  and  NetLogo  (Wilensky, 1999) include the concept of the ‘Model’, or ‘Observer’, itself; that is, a controller object that performs such processes.

        By “in what order?” we refer to both the order in which the different processes are executed and the order in which a process is performed by a set of agents. For example, feeding may be a process executed by all the animal agents in a model, but we must also specify the order in which the individual animals feed; that is, whether they feed in random order, or fixed order, or size-sorted order. Differences in such ordering can have a very large effect on model outputs (Bigbee et al., 2006; Caron-Lormier et al., 2008).

    The question of when variables are updated includes the question of whether a state variable is immediately  assigned  a  new  value  as  soon  as  that  value  is  calculated  by  a  process  (asynchronous updating), or whether the new value is stored until all agents have executed the process,  and  then  all  are  updated  at  once  (synchronous  updating).  Most  ABMs  represent  time simply  by  using  time  steps:  assuming  that  time  moves  forward  in  chunks.  But  time  can  be represented  in  other  ways  (Grimm  and  Railsback,  2005,  Chapter  5). Defining a model’s schedule includes stating how time is modeled, if it is not clear from the ‘Entities, State Variables, and Scales’ element.