# ModelDefinition The `ModelDefinition` general node defines system-wide information about the simulation. Example: ```python ModelDefinition { StartDate = "01-01-2024" EmissionsLifetime = 100 } ``` ## Attributes ### StartDate This attribute sets the start date of the simulation. * **Data type**: `date` * **Example values**: + `"01-01-2024"` + `"01/01/2024"` * **Default**: None. Must be provided by the user. ### EmissionsLifetime This attribute determines the emission lifetime used to calculate the Global Warming Potential (GWP) value for the computation of CO₂ equivalent emissions. * **Data type**: `Float` * Example value: `20` * **Unit**: Years * **Minimum value**: 0 * **Default**: 100