Comparative Classification of Multi-User Virtual Worlds Tony Manninen & Jani Pirkola Raahe Computer Laboratory of Oulu University Rantakatu 1, 92100 RAAHE, Finland
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Abstract This paper defines and describes the classification of heterogeneous and otherwise abstract multi-user virtual environments. Furthermore, the aim of the paper is to compare the most critical features of the worlds, and thus, to establish solid foundation for the development of ideal multi-user virtual world. Total of 15 virtual worlds have been selected for qualitative survey, which includes measurement and comparison of the critical features. Based on the survey, an analysis will be provided with the aspect of ideal system in mind.
1. Introduction The scope of applications and forums that can be considered as multi-user virtual worlds is very wide and heterogeneous. These computerised realms provide usability at every level, starting from the plain text-based chat worlds with minimal scenery objects, and ranging all the way down to the modern 3D enhanced virtual landscapes filled with avatars capable of full-scale interaction. Although the differences are great and the similarities sometimes difficult to notice, all of the applications share some basic attributes: they are virtual, they present a world or any part of it, and they can have multiple simultaneous participants. In order to formalise and clarify the heterogeneous concept of shared places, the aim of this paper is to survey the existing multi-user virtual worlds, to classify the worlds into major categories, and to compare these worlds with each other. The comparison of the worlds with the imaginary and ideal multi-user environment will also be conducted. At first, the definition of multi-user virtual world should be obtained and unambiguously defined. When separated into different expressions, the phrase multi-user virtual world would define computer-generated nonphysical surroundings, which could accept computeraided participation of several simultaneous users (i.e. online users). The on-line users will be able to wander
around the computer presented world, see and communicate with avatars representing other on-line users, and possibly to pursue some pre- or self-defined goal. Multi-user virtual worlds may also be defined, according to Damer, as two and three-dimensional graphical environments inhabited by users represented as digital actors called "avatars". Through this medium, a wide variety of Internet users are participating in a large scale social experiment and collaborating on a variety of projects [Dam97b]. In this paper, the definition is expanded to contain non-graphical text-based environments also, corresponding to the large number of applications and significant realisations. The field of the survey is further limited with the aid of brief preliminary and quantitative study. Based on the results of the quantitative study, the minimal number of categories with the maximal number of existing applications will be created. The significance of the survey is in classification and comparison of the current multi-user virtual worlds and thus, the acquirement of the most critical features defining an adequate application. Based on these features, further work may be conducted in defining and specifying the ideal multi-user virtual environment.
2. Survey of Existing Work The survey of existing multi-user virtual worlds is based on the information obtainable through Internet because of the fast development in the field, and the suitable medium for network concepts. Some of applications have been tested by the authors, while the evaluation of others is purely relying on the written and graphical material provided by other sources i.e. the reviewers and developers. The categorisation of surveyed applications is divided into two-dimensional classification. The first classification dimension is based on the user interface and presentation technology and includes the division of applications into text-only, 2D, and 3D graphics. The second classification dimension is based on the field of the application i.e. educational, game, social/chat,
creative and work/research. Table 1 presents the classification of the Multi-User Virtual Worlds. All of the surveyed applications fit into this classification framework, although some of the categories had to be left empty because of the lack of applications.
On the other hand, there surely are existing applications designed to be used within totally different field. For example, lack of industrial simulations seems to be quite strange.
Table 1. Classification matrix of surveyed multi-user virtual worlds. Technical Category TEXT Application Area Creative/Constructivist Educational/Training Game
Social/Chat
2D
AlphaWorld APECKS Dark Chambers BatMUD
Ultima On-line The Realm
IRC
Worlds Away
Work/Research
The following paragraphs describe each application and the main features of the virtual world. The subjects selected for this survey are meant to form a qualitative approach to the field, and they will by no means represent every aspect of the numerous multi-user virtual worlds available today.
2.1
Text-based Applications
Text-based multi-user virtual worlds are the oldest applications within the field. They contain no graphical elements, and thus, base their representation solely on the text. The atmosphere and level of immersion is mainly realised in the mind of the user. This, in turn, requires good imagination and visualisation capabilities from the participants. 2.1.1
IRC
Internet Relay Chat (IRC) is text-based communication forum, which consists of hundreds channel. The users may participate in the large field of discussions, either publicly or privately within selected members. 2.1.2
3D
APECKS
APECKS (Adaptive Presentation Environment for Collaborative Knowledge Structuring) is the educational and research World Wide Web Multi-User Dungeon Object-oriented (WWW-MOO), which is used as a textual study and research forum for researchers and students all around the globe [Ten97].
2.1.3
Meridian59 Quake WarBirds Worlds Chat Blaxxun Onlive Traveler DIVE
Dark Chambers
Dark Chambers is one of the many Multi User Dungeons (MUDs) that have been entertaining Internet society for several years [Bar90]. This text-based role-playing game functions around character development and team play. Dark Chambers could be described as an interactive book, which will largely base on the imagination of the user. 2.1.4
BatMUD
BatMUD is the representative of separate branch of Multi User Dungeons than Dark Chambers. The basic features are alike, and only some minor differences can be found. BatMUD originates from the LPMud, and is thus one of the most popular multi-user virtual worlds among Internet users [Bat97].
2.2
2D-based Applications
The applications within 2D class present their worlds using 3rd person view and picture like scenery. The viewpoint of the user is usually either from top (bird view), or from one side. This category utilises avatars as an illustration of the user, which provides reasonable navigation support even in the complex worlds. 2.2.1
WorldsAway
WorldsAway is a technology and application, which is based on the LucasArts’ project called Habitat. The
concept is fully modified by Fujitsu, and is currently offering socialising possibilities for thousands of Internets users. Within a community inhabiting a magical world called The Dreamscape, the user can interact with other participants, and even with the virtual economy of the world. Also in WorldsAway the user can join group games including bingo, and engage plenty of other social antics. Avatar costuming is one of the favourite activities within the world [Dam97a]. 2.2.2
Ultima On-Line
The network version of famous Ultima Role Playing game allows thousands of people to exist simultaneously in the same fantasy game world over the Internet. Players can enjoy true social interaction with other participants in real time — form adventuring parties, engage in battles with other players, take on perilous quests, or chat in a tavern over a goblet of virtual wine. Other elements of the game constantly evolve — a functioning virtual ecology drives monsters to roam in search of food if it's scarce, and world events are inter-related through a closed economic system and limited resources [Ori97]. The world of Ultima is presented in isometric 3rd person view with the avatar of the user being the point of focus. There are numerous computer-controlled creatures and hundreds of other objects in this huge world (according to the Ultima OnLine developers, it would take 10 hours to walk from one end of the world to the other). 2.2.3
The Realm
The Realm is the virtual world and on-line Role Playing Game (RPG) provided by Sierra On-line. The world consists of thousands of separate rooms, which are presented from the side using 3rd person view. The user may explore the locales of the world and chat with fellow Realmers from all over the real world [Sie98].
2.3
3D-based Applications
The 3D-based applications form the technological elite of multi-user virtual worlds. They use 3D models to illustrate the various aspects of the surroundings, and thus, create most realistic representation of the “real” world. The applied technologies are either based on the standard Virtual Reality Mark-Up Language (VRML), or the technology is implemented for the purpose, and is thus, application specific. 3D worlds may have avatar to present the user, or they will provide direct 1st person view.
2.3.1
AlphaWorld
With the Active Worlds Browser the user can explore and build in AlphaWorld and the Active Worlds universe. The world contains huge complex of cityscapes has the total number of 300,000 registered citizens and tourists. In the Active Worlds virtual cityscapes there is the possibility to interact with other citizens through text chat and build new establishments as easy as using Lego bricks. Active Worlds have other features, including music and sound effects, letting the user jam and dance with avatars that can move through articulation [Dam97a]. The total area covered is about 400sq kilometres, and would take over 2 hours to walk directly from one end to the other. AW is the first 3D environment in the Internet, opened June 28th 1995. Besides the homeworld AlphaWorld, there are over 300 other worlds owned by private people or companies. 2.3.2
Meridian59
Meridian59 could be described as graphical 3D MUD because of the many similarities with the text-only role playing games. The perspective of the player is 1st person, similar to Quake, which can be a bit more engrossing than third-person views where the player merely controls an icon or figure. The world of Meridian59 is not very large and the on-line building option is not available for the users. The world is also quite limited and there are many access restrictions for the users (e.g. forests can be explored through certain paths). The interface allows the player relatively easy access to whatever is needed [Hac97]. 2.3.3
Worlds Chat
The Worlds Chat is a VRML-based 3D chat world, which consists of several locations forming a space hub. It is a space station with dozens rooms and spacepods connected by hallways and escalators. The user can select his or hers avatar, and wander around the hub chatting with other participants through text chat. Worlds Chat citizens cannot change objects or build (which helps make the world so fast). There are some animation and sound effects such as Trek-like sliding doors cheesy and spooky MIDI music and the escalators rumble like old department store models [Dam97a]. 2.3.4
Blaxxun
Blaxxun interactive has opened the doors to the VRML club in Cyberspace. The user can access the world using Netscape browser with the Community Client Pro
3.0 plug-in. The world is built with VRML (the Virtual Reality Modeling Language). VRML is open, and this means that the user can build his or her own world and avatar with VRML and connect it to the vast and expanding labyrinth of blaxxun worlds. Chat with other participants is possible in text or Cooltalk voice (if the user has the correct Netscape plugin), or even with Microsoft NetMeeting [Dam97a]. 2.3.5
Quake
Quake is a fast pace 3D multi-user game from ID Software. The world of Quake contains detailed and architectural places of various natures. The high-quality world model results in quite restricted and non-scalable maximum size of the environment. Quake is one of the many 3D multi-user game applications providing realistic gaming experience for limited number of users [Id97]. 2.3.6
DIVE
The Distributed Interactive Virtual Environment (DIVE) is an internet-based multi-user VR system where participants navigate in 3D space and see, meet and interact with other users and applications. DIVE is especially tuned to multi-user applications, where several networked participants interact over a network. DIVE applications and activities include virtual battlefields, spatial models of interaction, virtual agents, real-world robot control and multi-modal interaction [Hag98]. 2.3.8
The applications under survey are quite heavily biased towards 3D solutions, which in turn predict the future development in this field. A wide variety of text-based systems are still used for many purposes, but with the advancements in current technology, the high-tech solutions will be more and more usual. In order to successfully compare the studied applications, the measures for comparison have to be defined. The selected measures should be easily identifiable and comparable, and thus, should not contain too abstract characteristics or features, which will be based on a subjective rating. The technical and user interface criteria used to evaluate and compare graphical multi-user virtual worlds have been adapted to suit for multi-user virtual worlds in general. The applied criteria include [Dam96 et. al]:
WarBirds
The Warbirds is a multi-user World War II flight combat simulator, which has 32 different aircraft to try out. The world of the Warbirds consists of hills, mountains and rivers, but the only structures depicted on the landscape are airfields. Users may team up, and have several types of co-ordinated campaigns against the enemy territories [Str97]. 2.3.7
3. Analysis
Onlive Traveler
Traveler from Onlive! Technologies is one of the most exciting revolutions to hit the Internet. The users can talk in their own voice to other people represented as avatars. The world is built using VRML and it includes for example a sophisticated avatar collision detection system with the corresponding sound effects [Dam97a].
1. Avatar appearance and design (range of choices, articulation or animation) 2. Ease, options for avatar motion (degrees of freedom, level of modelled features) 3. Methods of communication (text chat, body language, audio, video) 4. Effectiveness of controls and services (doors, stairs, walkways, rooms, signage, co-ordinate readouts) 5. Ability of users to alter the space (object moving and assembly, building construction, message posting) In addition to these criteria, a set of measures has been chosen according to the differences and distinctions of each application category. The approach starting from the ideal multi-user virtual world system has been chosen to form the foundation for the measure collection. Based on the literature and subjective opinions of the authors, the set of approximately thirty measures was identified. The verification and evaluation of these measures within each surveyed application is presented in the competence matrix illustrated in Table 2. The four different levels of realisation were used to evaluate and compare the measures. These levels include three shades of grey ( : : ) presenting the realisation level of the feature (darkest grey illustrates most full and/or most adequate realisation), and empty cell ( ) describes non-existent feature or poor realisation.
Table 2. Competence matrix of surveyed multi-user virtual worlds.
none
low
The applications have been classified based on the user interface and presentation technology, and thus, including categories: text-only, 2D, and 3D. Selected measures have been grouped into five separate classes:
medium
high
scalability, avatar features, world realism, user interface, and communication. When examining the matrix, distinct groups of measures and applications may be formed. For example, sound has been supported in most of the
applications, which also support either 2D or 3D graphics. According to the competence matrix, it is clearly visible that several areas of technology and features have been inadequately utilised within multi-user virtual world applications under survey. The usage of advanced input and output devices is almost non-existent within the surveyed group of applications. The current price range of the modern I/O system could be one of the reasons restricting the full-scale usage of the peripherals within entertainment and non-research sectors. Furthermore, the level of AI and the number of artificially intelligent objects seem to be one critical area of development. Even if the current technology provides adequate support for AI implementation, the realisation level seems to be quite low. One of the reasons could be the nature of the multi-user systems, which emphasises human-interaction, and thus targets the production resources elsewhere. Table 3. Overall Technology Comparison.
TEXT
2D
3D
applications lack some of the critical features, but on the other hand, every critical feature may be found at least in some of the applications. This corresponds to the fact that the technological background is more or less available, but there seem to be major difficulties in integrating all of the required features into one solution.
4. Further Work The further work within the scope of this survey must be continued in terms of keeping up to date with the development of this fast-evolving field. New applications and technologies will be introduced frequently, which in turn alters the results of this survey. The further identification and isolation of the most critical measures and features should be conducted for more detailed, more accurate and widely interdisciplinary viewpoint. These measures will then be used as a basis for the specification and design of ideal multi-user virtual world. The prototype of the world will be produced according to the specification and allocated funding.
5. Conclusions
Scalability Avatar Features World Realism User Interface Communication
The average values of different measure groups are presented in Table 3. The comparison between separate technical categories results in amazingly small differences. The World Realism measure group containing the easiness of the immersion has even the same average values within each category. Text-based VEs have been termed a `cold' medium, in which the users of the system tend to engage their imagination to fill in details, as compared to the `hot' medium of graphical VEs [Cur92]. It may well be that the use of imagination enhances the immersion that users experience [Ten97]. The modern 3D-based multi-user systems seem to lack adequate avatar features. Most of the applications model only few characteristics of the avatar, and illustrate even less. The text-based worlds have an advantage in this area, because of the strong and rich language support. The communication features have been most fully supported within the 3D applications. This may resulting from the current status of development i.e. 3D multi-user worlds are usually the most recent ones, and furthermore, they seem to contain better possibilities for integration of audio and video “terminals”. Currently, there seem to be no perfect, or even adequate, multi-user virtual world. All of the surveyed
While the early prototypes of multi-user virtual worlds suffered from both user interface and communication limitations, they were able to provide meaningful interaction within these digital spaces. Improved graphics rendering and server crowd control speed would reduce the effort required to navigate and approach other avatars for interaction. Further exploitation of auditory features, such as, speech and interaction cues, would greatly reduce the confusion and improve the usability. Finally, a set of simple, standard interface cues for navigating in virtual space would be very useful. There are also limitations that prevent the full expression of interaction, for example, because avatars are not unique to each user, it is difficult to distinguish between strangers and familiar users. Lastly lacking a means to identify who is involved in a conversation leads to frequent inadvertent interruptions [Dam96 et. al]. The ideal, or at least perfect, multi-user virtual world could be specified and developed with the seamless implementation and integration of the critical features. There are several existing applications, which have great potential for becoming an ideal solution. The complexity and wideness of this application domain seem to require too many compromises, and thus, restrict the current implementations. Although, we still do not have the ideal multi-user virtual world, the current implementations could be further developed to serve wide variety of needs. And even on today’s world, the applications provide adequate research and entertainment value.
6. References [Dam97a] B. Damer: Avatars! : Exploring and Building Virtual Worlds on the Internet, PeachPit Press, 1997 [Dam97b] B. Damer: Interacting and Designing in Virtual Worlds on the Internet, Proceedings of ACM CHI '97, 1997. [Dam96] B. Damer, C. Kekenes, T. Hoffman: Inhabited Digital Spaces, Proceedings of ACM CHI '96, 1996 [Dod97] C. Dodsworth: Digital Illusion, ACM Press, 1997. [Rhe93] H. Rheingold: The Virtual Community, AddisonWesley, 1993 [Pan97] I. Paniaras: Design of Virtual Identities and Behavior in Cyber Communities, Proc. 85th CAA Conference, 1997 [Gos94] R. Gossweiler, R. J. Laferriere, M. L. Keller, R. Pausch: An Introductory Tutorial for Developing Multi-User Virtual Environments, University of Virginia, PRESENCE: Teleoperators and Virtual Environments, MIT Press, 3(4), Fall, 1994, pp. 255264. [Bar90] R. Bartle: Interactive Multi-User Computer Games, MUSE Ltd and British Telecom, 1990 [Ori97] Origin, Ultima OnLine WWW-site, WWW-source: http://www.owo.com/, 1997 [Hac97] J. Hachem: Meridian 59 Review, Games Domain Review, WWW-source: http://gamesdomain.uol.com.br/gdreview/zones/revi ews/pc/jan97/merid.html, 1997
[Str97]
[Hag98] [Cur92]
[Ten97]
[Sie98] [Bat97]
[Id97]
C. Strachan: Air Warrior II and Warbirds, Games Domain Review, WWW-source: http://gamesdomain.uol.com.br/gdreview/zones/revi ews/pc/may97/airoff.html, 1997 O. Hagsand: The DIVE Home Page, WWW-source: http://www.sics.se/dive/dive.html, 1998 P. Curtiss: Mudding: Social Phenomena in Textbased Virtual Realities, Proceedings of Conference on the Directions and Implications of Advanced Computing, 1992 J. Tennison: Adaptive Presentation Environment for Collaborative Knowledge Structuring (APECKS), WWW-source: http://www.psyc.nott.ac.uk/staff/Jenifer.Tennison/A PECKS/ Specs/Initial/, 1997 Sierra On-Line, Inc: The Realm, WWW-source: http://www.realmserver.com, 1998 Balanced Alternative Techniques Ry: “Home Page of the BatMUD”, WWW-source: http://www.bat.org/, Balanced Alternative Techniques Ry, 1997 ID Software Inc.: Quakeworld, WWW-source: http://www.idsoftware.com/quakeworld/, iD Software, 1997
