Collection

Collections build on the ability of relationships to identify objects in a USD scene. Whereas a relationship is (resolves to, by fetching its Targets) simply an ordered list of paths identifying other objects in the scene, a Collection uses a pair of relationships and extra rules to compactly encode potentially large sets of objects by identifying a set of paths to hierarchically include in the Collection, and a separate set of paths to hierarchically exclude. For example, the following Collection identifies all of the prims comprising the two buildings, except for all the prims organized under the Floor13 prim in each.