Declarative Model

Declarative models differ from an imperative model in that actions
and conditions in which specific actions (individually or collectively) might be taken are not specified in advance but instead, emerge from simulations produced with the declarative models. 

An imperative model specifies the process to be followed and the initial conditions of the process then determine the outcomes. 

Two classes of declarative models are systems dynamics models and declarative agent-based models . The processes leading to outcomes and the outcomes themselves emerge from simulations with these models. 

The principal difference between declarative agent-based models and systems dynamics models is that the agent-based models describe social interactions whilst the systems dynamics models do not.