Is there an Intermediate Representation of URDF and SDF?

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When going from a URDF or SDF file to a simulated world, it is often useful for there to be an Intermediate Representation (IR). Benefits include:

1. Decoupling the XML parsers from the methods that create the actual simulation objects.
2. Performing some computation to fill in missing details in the IR like certain frame transformations, which joints form kinematic loops, etc.
3. Identifying errors in the URDF and SDF specification so the system can fail fast.

Does an IR already exist between the URDF and SDF parsers and a Gazebo simulation? If so, where can I find it?