It's like The Sims (Maxis TM)---people, their interactions, their world, and objects in the world are represented. However, activities are modeled in Brahms in more detail, beliefs and how they change are explicitly modeled, and focus of attention (what people notice in the world) is also simulated (based on what people think they are doing). In particular, communications are modeled in much more detail, plus the logistic interactions are represented (e.g., you need to know a fax number for sending a fax; how do you find out the fax number?). In the Brahms framework, how people behave depends on their group memberships/identities. People belonging to the same group behave similarly. Behaviors are "blends" of all the groups to which the person belongs. Finally, the simulation display allows finding out why simulated people did what they did and how their behaviors influenced each other.
In Brahms, people are called agents. Each agent has
his/her own beliefs, which may be specified when the simulation
begins (at both the agent or group level). Agent behaviors are
specified by situation-action rules, called workframes.
A workframe has a logical precondition (beliefs required for workframe to be activated), actions (primitive with durations, communications, movement, etc.), and consequences (changed beliefs or facts in the world).
A workframe's detectables specify what types of objects/attributes the agent might observe in the world while doing the actions.
An activity is modeled as an organized collection of workframes (e.g., alternative behaviors or steps in a procedure).
An optional end condition specifies how the activity might be satisfied, impassed, or aborted.
Workframes that do not have actions and so do not take time are called thoughtframes.
In the jargon of AI, each agent is essential a "knowledge-based system"; the simulation engine coordinates the processing of each agent's behaviors.
Objects, such as telephones, rovers, etc. are modeled similarly, except they are organized into classes and do not have thoughtframes.