Hierarchies describe the relationship between objects, usually using a combination of parent-child and tree analogies, as you do with a family tree. Objects can be associated to each other in a hierarchy for a number of reasons, such as to make manipulation easier, to propagate applied properties, or to animate children in relation to a parent. For example, the parent-child relationship means that any properties applied to the parent (in branch mode) also affect the child.
In a hierarchy there is a parent, its children, its grandchildren, and so on. The combination of links that can be created is almost infinite.
• A root is a node at the base of either a branch or the entire tree.
• A tree is the whole hierarchy of nodes stemming from a common root.
• A branch is a subtree consisting of a node and all its descendants.
• Nodes with the same parent are called siblings.

Topics:
• Selecting Objects in a Hierarchy.
• Cutting Links in a Hierarchy.
• For information about hierarchies and transformations, see Transformations and Hierarchies [Transformations].
• For more information on hierarchies specific to skeletons, see Building Skeletons [Character Animation].
• Parent-child links act like constraints in many ways. If you want to have objects move together without them being in a hierarchy, you can use constraints. For more information, see Animating with Constraints [Animation].
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