Croquet Project

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Croquet Project
Paradigm Object-oriented
Appeared in 2007
Designed by Alan Kay, Julian Lombardi, Mark P. McCahill, Andreas Raab, David P. Reed, and David A. Smith
OS Cross-platform
License MIT License
Website http://croquetconsortium.org

The Croquet Project is an international effort to promote the continued development of Croquet, a free software platform and a network operating system for developing and delivering deeply collaborative multi-user online applications. Croquet was specifically designed to enable the creation and low-cost deployment of large scale metaverses.

Implemented in Squeak Smalltalk, Croquet features a network architecture that supports communication, collaboration, resource sharing, and synchronous computation among multiple users. It also provides a flexible framework in which most user interface concepts can be rapidly prototyped and deployed to create powerful and highly collaborative multi-user 2D and 3D applications and simulations. Applications created with the Croquet Software Developer's Kit (SDK) can be used to support highly scalable collaborative data visualization, virtual learning and problem solving environments, 3D wikis, online gaming environments (MMORPGs), and privately maintained/interconnected multiuser virtual environments.

Contents

[edit] The Croquet SDK

[edit] Technical functionality

Real time, interactive, 3D map of this very same world. Change something in the world, the map changes. Move something in the map (as one would a chess piece), the object in the world represented by it moves the same way.
Real time, interactive, 3D map of this very same world. Change something in the world, the map changes. Move something in the map (as one would a chess piece), the object in the world represented by it moves the same way.

The Croquet technologies are presently available in the form of a software developer's toolkit (SDK) that can be used to develop deeply collaborative virtual world applications. Applications created using the Croquet SDK are automatically collaborative since application objects in Croquet share a common protocol that allows them to cooperate with each other.

Croquet works by employing the principle of replicated computation (synchronization) together with a peer-based messaging protocol that makes it possible to coordinate the activities of people within virtual worlds without the requirement of maintaining central server resources (other than those needed for specialized data and institutional middleware services).

Media content authors, programmers, and those moving through and interacting with the Croquet world simultaneously participate and collaborate in a dynamic, concurrent environment where they can work, explore, and learn at a level of integration not easily achieved through other virtual world technologies.

Underlying Croquet is an object-oriented semantics based on active objects that have the capability of temporal reflection. That is, each object is aware and in direct control of its behavior in time. Croquet also directly supports replication of computation, allowing computation to be moved close to the point of interaction on demand, while maintaining a consistent view of behaviors that can scale to include thousands of nodes. Consequently, Croquet is defined so that replication of computations is just as easy as replication of data. The overall effect is to greatly reduce the overhead required for widespread deployment of collaborative virtual worlds. This efficiency, combined with the ability to deploy Croquet worlds on consumer-level hardware, makes it possible to deploy large-scale and highly-participatory collaborative worlds at very low cost compared with virtual world technologies that are entirely dependent on server-based infrastructures to support the activities of their users.

[edit] Virtual machine

Adding 3D Notes linked to 3D Objects & Places
Adding 3D Notes linked to 3D Objects & Places

Croquet’s virtual machine (VM) runs bit identically on multiple platforms and it supports a number of capabilities that could only be provided by a true late bound, message sending language. Croquet’s relationship to Squeak gives Croquet the property of a purely object-oriented system allowing for significant flexibility in the design and the nature of the protocols and architectures that have been developed for the system. Because of this, Croquet has the ability to keep running while testing, and especially while changes are made – an essential part of the Croquet collaborative development capability. Programmers can therefore modify the code running the environment while the environment is running. Another key feature of Squeak is its generalized storage allocator and garbage collector that is not only efficient in real-time (so that animations and dynamic media of many kinds can be played while the garbage collector is collecting), but that allows reshaping of objects to be done safely. Like Squeak, Croquet supports many non-English languages and fonts such as German, Spanish, French, and Japanese.

Croquet allows the user to edit the source code of the 3D world from within the world, and immediately see the result while the world is still running. The running program does not have to be ended, and there is no compile-link-run-debug development loop. Any part of the program may be edited, down to the VM & OpenGL calls.
Croquet allows the user to edit the source code of the 3D world from within the world, and immediately see the result while the world is still running. The running program does not have to be ended, and there is no compile-link-run-debug development loop. Any part of the program may be edited, down to the VM & OpenGL calls.

[edit] Synchronization architecture

Croquet's time-based synchronization capabilities enable real-time, identical interactions between groups of users while dramatically reducing the need for server infrastructures to support virtual world deployment. Croquet's architecture makes it easy to develop deeply collaborative applications without having to spend a lot of effort and expertise in understanding how replicated applications work.

TeaTime is a scalable real-time multi-user architecture that is the basis for Croquet's object-object communication and synchronization. It is designed to support multi-user applications that can be scaled to massive numbers of concurrently interacting users in a shared virtual space. The most directly visible part of this architecture is the TObject class which is used to define and construct subclassed Tea objects. All of the interesting objects inside of Croquet are constructed from subclasses of TObject.

A Tea object acts with the property that messages sent to it are redirected to replicated copies of itself on other users' participating machines in a peer-to-peer network. This messaging protocol supports a coordinated distributed two-phase commit that is used to control the progression of computations at participating user sites. In this way messages may be dynamically redirected to large numbers of users while maintaining the appropriate deadline-based scheduling. Thus, TeaTime is designed to allow for a great deal of adaptability and resilience and works on a heterogeneous set of resources. It is a framework of abstraction that works over a range of implementations and that can be evolved and tuned over time, both within an application and across applications.

Key elements of the TeaTime synchronization architecture include:

  • A coordinated universal timebase embedded in communication protocol
  • Replicated, versioned objects that unify replicated computation and distribution of results
  • Replication strategies that separate the mechanisms of replication from the behavioral semantics of objects
  • Deadline-based scheduling extended with failure and nesting
  • Coordinated, distributed two-phase commit that is used to control the progress of computations at multiple sites, to provide resilience, deterministic results, and adaptation to available resources
  • Uses distributed sets

[edit] Cobalt

Cobalt user interface
Cobalt user interface

Cobalt is an emerging multi-institutional community software development effort to deploy an open source production-grade metaverse browser/toolkit application built using the Croquet SDK. Cobalt was made available under the Croquet license as a pre-alpha build in March 2008.

[edit] The Croquet Consortium

The Croquet Consortium is an international alliance of industry and academic institutions and individuals that seek to promote a broad collaborative open source metaverse software and toolkit effort. The consortium seeks to advance and promote the development, application and widespread adoption of open source Croquet technologies in research, industry, and education and to coordinate large-scale institutional participation in Croquet-related initiatives. The consortium is presently funded by major corporations, governmental agencies, universities, smaller companies, and individual donors. Members include:

Croquet Avatar with Wireframe Portal, eToy, & Mirror
Croquet Avatar with Wireframe Portal, eToy, & Mirror

[edit] History

Croquet is the confluence of several independent lines of work that were being carried out by its six principal architects, Alan Kay, David A. Smith. David P. Reed, Andreas Raab, Julian Lombardi, and Mark McCahill. The present identity of the project has its origins in a conversation between Smith and Kay in 1990, where both expressed their frustration with the state of operating systems at the time.

In 1994 Smith built a working prototype of a two user collaborative system that was a predecessor of the core of what Croquet is today. Also in 1994 Mark McCahill's team at the University of Minnesota developed GopherVR, a 3D user interface to Internet Gopher to explore how spatial metaphors could be used to organize information and create social spaces. In 1996 Julian Lombardi approached Smith to explore the development of highly extensible collaborative interfaces to the WWW. Later, in 1999, Smith built a system called OpenSpace, which was an early-bound variant of Croquet. Also in 1999, Lombardi began working with Smith on prototype implementations of highly extensible collaborative online environments based on OpenSpace. One of these implementations was a prototype implementation of ViOS, a way of spatially organizing all Internet-deliverable resources (including web pages) into a massively-scaled multiuser 3D environment.

Smith and Kay officially started the Croquet Project in late 2001 and were immediately joined by David Reed and Andreas Raab. Reed brought to the project his longstanding work on massively scalable peer-to-peer messaging architectures in a form deriving from his doctoral dissertation that was published in 1978. The first working Croquet code was developed in January 2002. Simultaneously and independently, Lombardi and McCahill began collaborating on defining and implementing highly scalable and enterprise-integrated architectures for multi-user collaboration and were invited by Kay to join the core architectural group in 2003.

From 2003-2006 the technology was developed under the leadership of its six principal architects with financial support from Hewlett-Packard, Viewpoints Research Institute Inc., The University of Wisconsin-Madison, The University of Minnesota, the Japanese National Institute of Communication Technology (NICT) and private individuals. On April 18, 2006 the project released a beta version of the Croquet SDK 1.0 in the open source. Since then, the Croquet technology infrastructure has been successfully used by private industry to build and to deploy commercial-grade closed source collaborative applications. Open source production-grade software implementations for delivering secure, interactive, persistent, virtual workspaces for education and training have at the same time been developed and deployed at the University of Minnesota, the University of Wisconsin-Madison, and The University of British Columbia.

[edit] Motivations

Multi-user, multi-lingual text editing in 3D
Multi-user, multi-lingual text editing in 3D

Alan Kay and Seymour Papert envisioned in the 1960’s the computer’s role as a tool for the mind… an “idea processor”. They have worked at bringing computers into this role for adults and children through several of Croquet’s predecessors like the Logo language and environment by Papert and Squeak, the open source Smalltalk language and environment, by Kay. In turn, for Croquet’s interface and architecture, Kay incorporated many educational principles discovered by Jean Piaget, Maria Montessori, and Jerome Bruner.

Croquet Spreadsheet
Croquet Spreadsheet

Kay and Papert expect computers (with the right software) to enhance learning and education through a media rich, enhanced communication medium and consequently benefit humanity in general as a result of the better communication of “powerful ideas”, ideas that “make the invisible somewhat visible”, ideas about truths that transform civilization’s thinking that are not common to all cultures but which must be discovered or invented by a culture and shared.

Kay’s philosophy suggests that if we consider science as an ever-improving mental map of causality as observed in the real world just as we observe cartography (map making) steadily improving our map’s accurate representation of the real world, we can consider Croquet as an ever-improving map of symbols and of place to reflect our understandings of science, the real world, and of each other.

To paraphrase Papert: In France, children grow up learning French fluently, just as we expect them to do. Yet, we have not allowed ourselves to imagine that children could all learn mathematics just as fluently as they learned their native language, if they grew up in a “Mathland”. Croquet, just as Squeak did earlier, tries to be that “Mathland” (and any other “land of an academic discipline” that its participants care to create for themselves and for each other).

Other educational principles incorporated by Kay and Papert include:

Kay and Papert consider Croquet and Squeak just one part of the two parts necessary to help humanity. They hope that Nicholas Negroponte’s $100 laptop effort, which they co-developed with him, will help distribute such learning, discovery, and communication software for youth around the world to use to supplement and improve the students’ own learning environments. In turn, they hope that these students’ discoveries and “powerful ideas” can be self-published by the same interconnected software to be made available to the rest of civilization.

[edit] Unique aspects

Croquet, as a software development environment, is more extensible than the proprietary technologies behind collaborative worlds such as Second Life, and before that ViOS. This is because;

  • It establishes a computational environment that belongs to its users;
  • It is platform and device independent;
  • Users/developers may freely share, modify and view the source code of the entire system (due to Croquet's liberal license);
  • The technology is not hosted on a single organization’s server (and hence not governed by any such organization);
  • It provides a complete professional programmer’s language (Smalltalk/Squeak), IDE, and class library in every distributed, running participant’s copy (the programming development environment itself is simultaneously shareable and extensible); and
  • Croquet based worlds can also be updated while the system is live and running.

Some of the environments that are enabled by Croquet somewhat resemble those of Sun's Project Wonderland. However, Croquet has been designed to go much further given that the programming of the 3D world is virtually without limits (due in part to Squeak's late-binding architecture and metaprogramming facilities) as well as Croquet's lack of dependency on server infrastructures as a means of supporting basic interactivity between peers.

[edit] See also

[edit] References

[edit] External links