Urbi is an open-sourcecross-platform software platform in C++ used to develop applications for robotics and complex systems. Urbi is based on the UObject distributed C++ component architecture. It also includes the urbiscriptorchestration language which is a parallel and event-driven script language. UObject components can be plugged into urbiscript and appear as native objects that can be scripted to specify their interactions and data exchanges. UObjects can be linked to the urbiscript interpreter, or executed as autonomous processes in "remote" mode.
The urbiscript Language
The urbiscript language has been created in 2003 by Jean-Christophe Baillie in the Cognitive Robotics Lab of ENSTA, Paris. It has been actively and further developed in the industry through the Gostai company founded in 2006. It is now an open source project, with a BSD license, available at . The urbiscript language can be best described as an orchestration script language: like Lua in video games, urbiscript can be used to glue together C++ components into a functional behavior, the CPU-intensive algorithmic part being left to C++ and the behavior scripting part being left to the script language which is more flexible, easy to maintain and allows dynamic interaction during program execution. As an orchestration language, urbiscript also brings some useful abstractions to the programmer by having parallelism and event-based programming as part of the language semantics. The scripting of parallel behaviors and reactions to events are core requirements of most robotic and complex AI applications, therefore urbiscript is well suited to these applications.
Integration of ROS directly accessible from urbiscript
Examples
The example below shows how to write a ball tracking action/perception loop in urbiscript: headYaw/headPitch are two motor objects, and ball is the ball detection object : whenever ;
whenever is used to trigger a piece of code in loops as long as the associated condition is true. The "&" sign is used to specify that both commands should start at the same time, thus running in parallel. Other notable event-driven constructs include at, which triggers the associated code once when the event is triggered: at
Every command or group of commands is taggable, which provides a way to stop it later if needed: myTag: while echo, at myTag.stop;
Note in the example above the comma at the end of the command. It will put the preceding command in the background, allowing the flow execution to carry on, in particular the next 'at' command to be executed.
UObject component architecture
The UObject component architecture allows developers to interface any Java/C++ object within Urbi, making selected methods and attributes visible in urbiscript, while in fact being compiled code. Special notifiers can be set on any of the object's attributes to notify the C++ side of any change on these attributes on the urbiscript/Urbi side. UObject uses C++ templates to transparently map any requested method to an interface machinery that takes care of the type checking. A UObject can be used in plugged mode if it is directly linked to Urbi at compile time or with dynamic loading. In that case, the C++ object shares the Urbi memory directly, resulting in efficient integration. This is typically used for time critical components like motor or sensor drivers. The same UObject can also be used without modifications as a remote component. In that case, it will become an autonomous program to be executed with the IP address of the Urbi server as a parameter. In both cases, the object will transparently appear in urbiscript as a native urbiscript object.
