An IfcWorkSchedule represents a task schedule of a work plan, which in turn can contain a set of schedules for different purposes. 

IfcWorkSchedule can reference a project (the single IfcProject instance) via IfcRelDeclares. The figure below shows the backbone structure of a work schedule that defines a context through IfcRelDeclares (not necessarily the project) and controls tasks (typically the schedule summary task) and resources. Please note that a work calendar shall be assigned to the summary task and not the work schedule. 

If an assigned IfcTask is a root-level task, such task must be declared on the IfcProject using the IfcRelDeclares relationship.