URBI

Key takeaways

URBI belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect URBI to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of URBI from memory before moving on to harder problems.

Reference excerpt

Urbi is an open-source cross-platform software computing platform written 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 urbiscript orchestration 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 was 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 on GitHub. 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 a program 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 (and the whole Urbi platform) is well suited to such applications.

Language attributes Parallelism and event-based programming Prototype-based programming C++ like syntax Java and C++ based component architecture (UObject) with possibility to link objects or run them remotely Client–server model architecture Cross platform: Linux, Macintosh, Windows, others. Embeddable, Urbi can run on various processors: x86, ARM, MIPS, powerPC, etc. Job control via "tags"

Functions Parallel programming and event-driven programming Programming prototypes Syntax similar to C++ Architecture components: C++, Java (UObject) with the ability to link object or execute remotely Client–server model Interfaces with customers Java and MATLAB (Urbi SDK) Multiple platforms: Linux, macOS, Windows NT, and embedded environments (x86, ARM, MIPS, powerPC) Marking orders for their control so asynchronous Integration of Robot Operating System (ROS) directly accessible from urbiscript (version 2.1)

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 (x and y range from -1/2 to 1/2):

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:

Every command or group of commands is taggable, which provides a way to stop it later if needed:

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.

Ecosystem

Robotics simulators compatible with Urbi Webots is the official robot simulator compatible with Urbi. Player/Stage integration has been reported, although it is not currently released.

Urbi-fied robots Released:

Gostai Open Jazz Segway PT Aibo ERS-7/ERS-2xx (Urbi 1.x only, Urbi 2.3 is available as alpha) iRobot Create Lego Mindstorms NXT HRP-2 (restricted release to members of JRL) Nao Robotis Bioloid Mobile Robots Pioneer Announced:

Surveyor Khepera III e-puck

Worked examples

Example 1 — a first encounter with URBI

Start with the simplest possible case. Write down what URBI claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to URBI before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about URBI ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of URBI

In research: URBI appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses URBI in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: URBI is common in secondary-school and first-year university syllabi. It links to neighbouring topics 2003 in robotics, 2003 software, Integrated development environments, so understanding it makes those chapters shorter.
In everyday life: Look for URBI outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study URBI in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what URBI means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain URBI out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is URBI in simple terms?

Urbi is an open-source cross-platform software computing platform written in C++ used to develop applications for robotics and complex systems. Urbi is based on the UObject distributed C++ component architecture.

Why does URBI matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study URBI?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on URBI.