URML (open robot intent language): a validated-intent layer that interops with BehaviorTree.CPP — request for comment

[idoco2003]

Hi BehaviorTree.CPP community,

URML (urml.dev) is a small, Apache-2.0 language for describing robot intent: a person writes a sentence, URML turns it into a typed primitive, validates it against the robot's declared capabilities and a safety envelope, then dispatches. URML has a Layer-3 of its own -- programs are trees of sequence / parallel / branch / retry over typed, validated primitives -- so I'm writing to the people who build the dominant behavior-tree engine to ask how the two should meet.

Nothing here asks the project to adopt, host, or maintain anything. This is a request for comment, and genuinely a design question.

Two seams, both honest: (1) URML lowers to a tree -- a validated URML program's sequence/parallel/branch/retry compiles to a BehaviorTree.CPP tree, each primitive a leaf, and URML supplies what BT leaves don't check on their own (typed args, capability match, safety envelope, all verified before the tree runs). (2) A leaf dispatches a validated primitive -- a custom BT.CPP / BT.ROS2 node wraps one URML primitive so a hand-authored tree gets validate-before-actuate per leaf. The acid test holds: a behavior tree is control flow; URML is the typed, capability-checked intent the flow carries.

Two real questions: (1) Which seam is more natural -- URML compiling to a BT.CPP tree, or a BT leaf node that dispatches a validated URML primitive? (2) Does URML's sequence/parallel/branch/retry map cleanly onto BT.CPP control nodes (Sequence/Parallel/Fallback/RetryUntilSuccessful), or are there mismatches?

Full write-up: https://github.com/URML-MARS/URML/blob/main/docs/rfcs/0470-behaviortree-cpp-outreach.md

Thanks for BehaviorTree.CPP; the de-facto robotics BT engine is exactly where this Layer-3 interop question should be asked.

Ido Yahalomi (URML, greenvh@gmail.com)

AI-assisted prose, maintainer-reviewed before posting (see VIBE.md). Human-only correspondence available on request.