using extended fuzzy-timing petri nets to modelrole-based and agent oriented collaborative virtual...

8/3/2019 Using Extended Fuzzy-Timing Petri Nets to ModelRole-Based and Agent Oriented Collaborative Virtual Environment

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Proceedings of the 5" World Congress on Intelligent Control % i i r a @ % ~ i % E # $3hk%e2004%'.fiR 15 - 19 E , 9Bfnl.i.ind Automation,June 15-19.2004. Hangzhou. P.R. China

Using Extended Fuzzy-Timing Petri Netsto ModelRole-Based and Agent Oriented Collaborative Virtual

EnvironmentHaihong Wul, C h u n y a n Yu' an d M i n g h u i Wu2

'State Key Lab.ofCAD&CG Zhejiang Universify.Hangzhoir, Zhejiang Province, China'Computer Department o Zhejiang UniversiiyCity College, Hungzhotr, Zhejiang Pro vince,China

[email protected]

Absfracl - Modeling collaborative virtual environment(CVE) is the basisof describing and solving related problemssuch as concurrency and consistency. In this paper, a newmodel adopting role theory for CVE is presented. Thisrole-based model called RACVEdefines CV E as a seven-tuplewhich contains all important components and describes staticrelations between basic rollaborative entities and collaborative

events. Especially, two important concepts,Intelligenr Entity inRunning Stare and Collaborative Federation,are proposed totake time factor into consideratian. Although the definitionand static relation description are com plete inRACVEmodel,it is still deficient in desrribing time-based dynamic statetransition of system. The RACVE model represents only atraditions) 3D system; actually, CV E s a kind of 4D systemwith time as its fourth dimension.In order to represent timefactor explicitly and describe dynamic state of system, aFuzzy-Timing Petri Nets formal modeling technique isemployed to revise RACVEmodel to satisfy 4D and real-timerequirement of CVE. Furthermore, state transitions forSharedObject, Intelligent Entity in Running Slate, Collabora~iveFederation, and Collaborolive Autiviware modeled efficiently,and reinforceRACVEgreatly a s well.

Index Terms- collaborative virtual environm ent,Fuzzy-Timing Pe tri Nets, fuzzy-timing, formal modeling, role scheme

1 INTRODUCTION

Collaborative Virtual Environment (CVE), whichintegrates CSCW (Computer Supported Collaborative Work)technology, VR (Virtual Reality) technology, AI technology,multimedia technology and network technology, is one ofthe important modalities of the next-generation computing

Due to the recent rapid development of all techniquesmentioned above, there are diverse applications andincreasing use of CVEs, such as virtual shopping mall,education, etc.

However, CVEs still have many problems to solvesuch as maintaining real-time consistency and concurrency.Some programming package and libraries are developedtohelp programming instead of formal modeling1'?Nevertheless, we insist that a formal model for CVEs is thebasis of describing and solving all these problems. As weh o w , C VEs allow people geographically dispersed tointeract with each other in real time, share information,manipulate objects, and work together to perform acomplex roup task in remote virtual environments overnetworksi5. Hence, it is difficult to model CVEs because i t

focuses on not only all virtual entities and interactionamong virtual entities hut also state transition of virtualentities accompanying interaction and time.ag ing.Also, it ismore complicated by adding network considerations, forconcurrency and consistency are network-correlated.

This paper consists of two phases: first, it proposes a

generic role-based model called RACVE for CVEs byintroducing role scheme; second, it proposes to apply aFuzzy-Timing Petri Nets (FTNs) formal modelingtechnique to R.4CVE in order to add time factor andnetwork considerations into it. The proposed genericRACVE model regards CVE as a 3D virtual environmentand an spatial extension for traditional2D CSCW system; itdescribes virtual entities and s tatic relations between virtualentities perfectly; moreover, it takes time factor intoconsideration: especially, the two important concepts areboth time-based defined: fntelligenf Enfity in RunningStarewhich represents hybrid avatar and virtual actor, andCollaboration Federation which is the minimum unit toprocess collaborative activities. However, integrating time

factor into ou r proposed model is pretty superficial for themodel don't describe state transition at all; thus, it stillcouldn't describe concurrency and consistency problems.Applying formal modeling techniques such as FTNs torevise OU T RACVE model, we hope to extend original 3Dmodel to a sufficient 4D model which can describe dynamicstate transition of CVEs and make i t conductive to describeand solve consistency and concurrency problems. In thispaper, we employ a kind of extended FTNs technique tomodel the effects that time factor acts onIntelligent E n t i pin Running Stare, Collaborative Federation, Shared Objectan d CollaborativeActivity.

This paper is organized as follows: section 2 presentsour role-based model M C V E which is a traditional 3D

model. Section 3 expands traditional 3D model toa 4Dmodel through introducing time factor and reviews brieflyFTNs. Section 4 proposes generic FTN models for four keyconcepts expanded fromou r role-based model RACVE.Ourconclusion is given in section 5.

11. TRADITIONAL 3 D MODELRACVE FORCOLLABORATIVE VIRTUAL ENVIRONM ENT

A CVE is composed of a number of entities whichsimulate those true objects in real life by representing3-Dobjects in higher-level and encapsulating all attributesof

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objects such as position and actions. Foran y CVE, there arethree essential entities: Hybrid Avatar, Virtual Actor andShared Object. Shared Objects existing in a CVE constitutevirtual objects that ffvbrid Av&r an d Wa rul Actor canoperate. Hvbrid Avatar embodies a participant in the virtualworld. He interacts with th e vittual world throughcontrolling his avatars motion; meanwhile, he recognizesthe other ones state position, and movement by theiravatars. As we know, Hybrid Avatar is a special entity as itis alterable, active and locomotor. Different from HybridAvatar controlled by its participant, Virtual Actoraccomplishes a specific task for collaborative activitiesself-determinedly and intelligently. Virtual Actordistinguishes itself from th e common agent because it isvisualized and has same movement as avatar.Hybrid Avatarand K m a l Actor, viewed as intelligent agents, are twoessential components supporting collaborative activities inCVEs.

In addition, we adopt the concept of role from roletheory[. As we know, Participants Roles and Rights is on eof generic requirements for collaborative activity inCVEs. That is to say, certain roles and associated withcertain rights must be appointed for each participant toensure efficiency and progressof the collaborative activities.Hence, all Hybrid Avatars an d Virtual Actors are playingthe roles according to their capabilities. A role, defined as acollection of duties and rights, refers to the expectedbehavior pattems an agent must perf orm Duties of roles aremodeled as obligations which specify what activities anagent must or must not perform on a set of shared objects.Rights are modeled as permissions which specify whatcollaborative activities an agent is permitted (or forbidden)

to perform on a set of target resources[8J. There are tw ogeneral types: particular role and time-based role.Particular role is inherent in agents, for instance,consumerfo r a Hvbrid Avatar and sales fo r a Ern id Actor are bothpaeicular roles that are unchangeable during the whole lifecycle of agents once these roles are assigned to. On thecontrary, time-based role is random for agents. That istosay, agent plays different roles at different time. Forinstance, when a user logging in a CVE af time tlh his avatarplays member role; and if he sponsorsa new collaborativesession at time t,, his avatar plays leader role. Agents areselected to play the time-based roles according to somespecial policies.

On the other hand, collaborative event describing the

dynamic process of collaboration is another importantconcept. Shared Object Manipulation, CommunicationandNuvigation are three basic collaborative events. SharedObject Manipulation,one of the most important interactionsbetween users and the virtual world, includes geometric,edit and transfer operations as well[]. That is to say, userscan select a certain shared virtual object to change itsposition and orientation, manipulate object attributes, andexecute application-predefined embedded functions.Comnnmication, which is the foundation of all kinds ofcollaborative events and interactions, assures progressesofal l collaborative activities even though it might he direct or

indirect and its effects might he explicit or implicit.Navigation, an important characteristic o f CV Es, providesasimple and natural method for users to move throughin aneasy manner to reduce spatial loss and enhance usersspatial awareness[.Definition 1 A generic role-based collaborative virtualenvironment model RACVEis a tuple

CV E = where Avatars represent all users in CVE where there existsone-to-one-mapping between Avatars and users;Actors isan aggregation of agents that automatically accomplishspecific assignments for users in CVE;SO is an aggregationof shared objects in CVE; R represents a se t of roles andcorresponding Role Schem e to supportall the collaborativeactivities in CVE; M represents Object Manipulation; Crepresents Communication;N represents Navigation. ,

Avatars, Actors and SO constitute a collaborativeentity layer of CVEs while Avatars and Actors are

collaborative activity subjects. AndM , C and N constitutebasic collaborative events. Furthermore, Fig.I shows ageneric architecture of our proposed role-basedcollaborative virtual environment model. As Fig..l shows,there are two important concepts introduced IntelligentEnti@ in Running State proposed to describe dynamic stateof Intelligent Entities that contain both Hybrid Avatars an dVirtual Actors, and Collaborative Federation defined as theminimum unit to p rocess collaborative activities.Definition 2 An Intelligent Entity inRunning State model isdefined in BNF as follows:,::=

INTELLIGEN T ENTITY IN RUN NING STATE

< Target_Role-Rule Associated List>END-INTELLIGENT ENTITY INR W I N G STATE< Target-Role-Rule Associated List>: := < RnleList(Goal, t< Target-Role-Rule Associated List? := < RuleList(Goa1,t)>

The attributes o f an Intelligent Entity in Running Statehave the following meaning: ID is the identifier of HybridAvutar or Virtual Actor to associate lntelligenf Entily inRunning State with avatars or actors unique correlativestatic definition. Variational Attributes involve allchangeable attributes that are time-based of avatar or actor.Rules is self-determined reaction rule base and its record isa set of clauses as follows: IF Conditional Statenient THEN

Executing Triggered Collaborative Event. Goal indicates acertain Collaborative Goal that the Intelligent Entit) . isengaged in at time t. Taxet is current .Target Statusdetermined by Goal. RoleList(Coa1, t) is a set of Roles an dfor an y r ER oleLis t (Go ul , t ) , r depends on Goal and time t.RuleList(Goa1,i) is a set of collaborative restriction ruleseduced from Goal and collaborative resource libraryincluding Collaborative Rules Base. CollaborativeFederation is a dynamic combination of Intelligent Entifiesin Running State.Definition 3 Collaborative Federation model is defined inBNF as follows:

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4 cExternal Virtual Environment

Fig. I A gencric architecturefor R A C V E

::="COLLABORATIVE FEDERATION "END-COLLABORATIVE FEDERATION"

::={","


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fuzzy enabling time, fuzzy occurrence time and fuzzy delay.For s implicity, trapezoidal possibility distributions specifiedby the 4-tuple (IT,, 2 , T, , n 4 ) re used to represent fuzzytim e fu nction s. Z ~ O U I ~ ~xtended FTN by integrating FTNwith timed Petri net. In Extended Fuzzy-Timing Petri Nets(EFTNs), each transition is associated with a firing intemalp ( a , p ) ,where the default interval is 1[0,0] (a transitiondefinitely fires as sqon as it is enabled). If a transitionT isenabled at time initant T , T may not fire before timeinstant r +a , nd must fire before or at time instant r + p .p is the possibility of transitions in structural conflict. Byattaching firing intervals with possibilities, these modelssucceed in giving a firing possibility and priority amongtransitions in conflict. The formal definitionof EFTNs andthe method to compute and update fuzzy time functions fortransitions are given in [12].

IV. REVISNG RACVEWITH EFTNs

As analyzed above, it is the fatal flaw of ourrole-based and agent oriented model that time factorintegration is too superficial. Undoubtedly, the task of toppriority of revising our RA CVE model is to represent timefactor and state transition explicitly, which is feasible byFTNs.

Our role-based model has been described the staticrelations between those basic collaborative entities andbasic collaborative events. That is to say, definition anddescription for static parts of CVEs is complete in ou rrole-based model. Hence, ou r revision work carried outwith EFTNs aims at reinforcingou r original model throughdescribing state transition of collaborative entities andcollaborative federation based on the original3D modelrather than overthrow it. In figure 2 to 6 , we model statetransition of Shared Object, Intelligent in Running State,Collaborative Federation and Collaborative Activityseparately.

In order to revise our role-based collaborative virtualenvironment more accurately, we introduce an special arcnamed du m p arc into ou r proposed models, which is subsetof the set of arc (P,T). The m ain feature of dump arc is thatits weight is alterable and depends on the number of tokensin its input place P. Once the output transition T is fired attime instant T , ll current tokens in the input placeP willbe taken off through the arc. To avoid frequent updatingserver database and federation copy, we employ dump arcto the updating actions, which not only solves the problem

caused by tokens heap but also describes the periodicalactions concisely. In the figures , we den ote such arcs by thecharacter n attached to the weights.

In the revised models, bur explicit timingconsiderations are embodied as follows. We use the timeinterval[ E , , E , ] or [ E ~ ,> ] to represent the period duringwhich local copy waits for reload from server database orfederation copy. To describe the duration of a certainactivity more explicitly, we combine the transition withappropriate fuzzy delay D,,,,.,, r ) uch as D E , D,,#,,

in Fig.2. Furthermore, we may assign the possibility totransitions in structural conflict, which is desirablein futureworks.

V. CONCLUSION REMARKS

In order to model CVE, we first have presented a newrole-based model RACVE in this model. And thecorresponding architecture has been given. The twoimportant concepts in RACVE are Intelligent Entihi inRunning State and Collaborative Federation. RACVEandits architecture define and describe the static relationsbetween basic collaborative entities and basic collaborativeevents completely. However, as the fourth dimension ofCVE, time factor do not represented explicitly inRACVEatall. Introduced FTNs, we have modeled state transition ofShared Object, Intelligent in Running State, CollaborativeFederation an d collaborative activity separately. Inparticular, we have introduced a new arc nameddump arc

in the above models to describe state transition much moreaccurately.

REFERENCES

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An agent ob tain the permissionofcreat io~l

Create a new iliared object

Shared object is created

Add shared object to DB

Sewer DB ,b updsrc shared object inUB y other fedemion s

Federationiequerl to load

Sewer DB is updatedFlag ofdelcie

An agent in federation

Shared

Ubiect's

llfecyele is OYer

Shared object isdestroyedin

this fedemtion

shared Obicct dclefed

Pemlanen, Al"tl"ip"latia" Z-Q

Five up Update sharedobject in DB

Fig. 2 EFTN model for thewhole lifecycle o f a shared objcct

Local agent requeiffo or d

is ready

Shared object out

of dirplayine area

Update federation's copyby other agents

Wait fo r Manipularion isWait for updatingfederation'scopy

Updare federation's copy Update sha rd civeobject in DB

Fig. 3 EFTN model Cor lifecycle of3

copy of a shared object

Agent log inFederation is reedy

Agent log cute oa d -Local scene s readylupdafed

Destroy local x r n r

collaborative goal

updating federation

Update fedcntioo U P b t e Givr upDB

Fig. 4 EFT 8 model forhfelligenr Entirv in Running Stare

Fig. 5 EFTN model for,Colluboralive ederalion

A new collaborative goal IS generated

evaluating ith fhc thresholdst

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Fig. 6 EFTN model far Colloborolive AcliL,iw

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using extended fuzzy-timing petri nets to modelrole-based and agent oriented collaborative virtual...

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