Relationships#

What is a Relationship?#

Relationships establish connections between prims, acting as pointers or links between objects in the scene hierarchy. A relationship allows a prim to target or reference other prims, attributes, or even other relationships. This establishes dependencies between scenegraph objects.

How Does It Work?#

Relationships store path values that point to other scene elements. When you query a relationship’s targets, OpenUSD performs path translations to map the authored target paths to the corresponding objects in the composed scene prims.

Relationships are robust against path translations, a key advantage over hard-coded paths. If a target prim’s path changes due to editing or referencing, the relationship automatically remaps to the new location.

Relationships can have multiple targets, making them useful for grouping or collecting objects together. For example, a material relationship might target all geometry prims that should use that material.

Note that a relationship is an alternative type of property to an attribute. Unlike an attribute, it has no data type. It is a way of declaring, at creation time, that the only use for a property is to record linkage information. Conceptually, it is like an attribute whose data type is a “link”. This means you can not use a relationship to connect two already-existing attributes–for that, you can use attribute connections.

Working With Python#

Here are a few Python commands to familiarize yourself as you work with relationships. These can be useful as you establish connections between different scene elements, like materials and geometry.

 1# Get the target paths of a relationship
 2UsdRelationship.GetTargets()
 3
 4# Set the target paths for a relationship
 5UsdRelationship.SetTargets()
 6
 7# Add a new target path to a relationship
 8UsdRelationship.AddTarget()
 9
10# Remove a target path from a relationship
11UsdRelationship.RemoveTarget()

Key Takeaways#

Relationships enable robust encoding of dependencies and associations between scene elements, such as:

  • Binding geometry to materials

  • Grouping prims into collections

  • Establishing connections in shading networks

  • Modeling hierarchical relationships (e.g. parent-child)

Using relationships instead of hard paths enhances:

  • Non-destructive editing workflows

  • Referencing and asset reuse across tools

  • Collaborative workflows across teams

Relationships are a way to link scene elements while enabling non-destructive editing and cross-tool collaboration. They enhance the flexibility and scalability of OpenUSD-based pipelines.