Most navigation properties translate into getting the objects on the other side of the relation from the object. A special case is Navigation Properties on the Plant object (ConfigProjectRoot in Smart 3D). As per OData specification, there is a Navigation Property on the Plant for each Entity type and these properties return an Entity Set of all objects of that type in the model, not just those that have a direct relation to the plant. However, there is also the need to be able to get only those objects that have an actual relation to the Plant. To accomplish this, additional Plant navigation properties, whose name ends in "Children", are created to only return those objects that have a direct relation to the Plant. For example:
GET <ServiceRoot>/Sites('MySiteAlias')/Plants('MyPlant')/Handrails
Returns all the handrail objects in the model.
GET <ServiceRoot>/Sites('MySiteAlias')/Plants('MyPlant')/HandrailChildren
Returns only those handrails that have an actual relation to the ConfigProjectRoot.