Static Separation of Duty (SSoD) differs from [Dynamic Separation of Duty] (DSoD) based on the when the enforcement of the [Separation of Duty] constraint is performed.

Static Separation of Duty is typically determined when the roles are assigned to the users. [Dynamic Separation of Duty] is dynamically evaluated within the active session. 

!!(SSoD) relations 
* prevents conflict of interests that arise when a user gains permissions associated with conflicting roles 
* (SSoD) relations are specified for any pair of roles that conflict. 

The [Dynamic Separation of Duty] concept becomes especially important when utilizing [RBAC Hierarchical] where a senior role may contain conflicting [Separation of Duty] constraints.