Software Agents in the Wireless World - Application to Mobile Services -

- Application to Mobile Services -

ZakariaMaamar

,WathiqMansoor

,andQusayH.Mahmoud '

Software AgentsResearchGroup@ZU

'

WITLab

College ofInformationSystems SchoolofComputingScience

ZayedUniversity SimonFraserUniversity

Dubai,UnitedArabEmirates Vancouver,Canada

zakaria.maamar,wathiq.mansoor@zu.ac.ae qmahmoud@cs.sfu.ca

Abstract Thepaperdiscusses mobileservices,denotedby m-services,

inthe wireless world. M-services are viewed as an extensionto the e-

servicesparadigm.Thewirelessworldhasitsownfeaturesthatmakeit

dierentfromthewiredworld.Forinstance,newcommunicationmeans

needto be used, newuser-friendly servicesneed to be suggested, and

newtypesof computingresourcesneedto be involved.The paperalso

discusses the use of software agents inaddressing the following issues:

howarem-servicesdiscoveredinanopenwirelessenvironment?Howare

m-servicescombinedtogether?Andhowarem-servicesmadeexecutable

onwirelessdevices?

1 Introduction

According to [3], the Internet is going throughseveral major changes. Indeed,

the Internet is becoming a vehicle of services rather than just a repository of

information.Currently,severalorganizationsaremakingtheirservicesaccessible

overtheweb.Usually,e-servicesdenotethiskindofservices.Besidesthenewrole

oftheInternet,weexpectthatmoreandmoree-serviceswillbeoeredtopeople

who use wireless devices to conduct their operations. Further, we expect that

moreandmorewirelessdeviceswillbeenhancedwithnewadvancedcomputing

resources,whichwillenabletheminthenearfuturetobecomemobileoces.We

areallwitnessingthetremendousgrowthinthedevelopmentanduseofwireless

devicesacrosstheworld.Unfortunately,thisgrowthisaccompaniedwithitsset

of problems.For example,wirelessdevices arestrictly bound to theirbatteries

for operation. In order to support wireless devices-oriented users 1

, we aim at

working on a new generation of e-services that will be specially designed and

developed to t wireless devices. M-services denote this new generation of e-

services.

Thereexistseveraltypesof wirelessdevices,varying frommobile phonesto

PersonalDigitalAssistants(PDAs).Thesedevicespresentseveralshortcomings

thatmaketheiruserequiresspecicarrangements.Forinstance,theservicesto

1

goes against the e-services platform independence principle. Thus, leveraging

e-services into m-services is a necessity. M-services will have to consider the

characteristicsofthewirelessdevicesonwhichtheywillberunning.Infact,we

advocatethatm-serviceswillbefetchedon-demandfromprovidersitestousers'

wirelessdevices.

Havingpre-installedservicesonusers'wirelessdevicesisanoptionthatcould

beconsidered. However,this optionwould haveworkedfor asmall number of

users where looking for the lowest commondenominator betweenthem is fea-

sible. In an open environment with dierent users and needs, looking for the

common denominator is not trivial. Therefore, on-demand deliveryof services

to wireless devices is more appropriate than pre-installing services. Enabling

thedownloadingof dynamicallycomposed servicesisamongtheapproachesto

followforsystemsdesignedtothewirelessworld.

Section 2motivates ourwork on m-services. Section 3denes mobile com-

puting and e-services. Section 4 presents our system of m-services. Section 5

describesoursystemimplementation.Section6presentsrelatedwork.Section7

concludesthepaper.Itismadeclearatthatlevelthatissuessuchasnegotiation

andcoordination,whileimportant,donotfall inthescopeofthispaper.

2 Motivating scenario

Tomotivate ourwork,weconsiderthefollowingctivescenario.Asales repre-

sentative working for a software company;it is based in countryX but serves

customers fromovertheworld. Sincetherepresentativeismostof thetimeon

themovevisiting customers,he isequipped witha PDA, which provides basic

oce tools. Moreover,the representativeuses the PDA to record the dealshe

madewithcustomers.Itmayhappenthatinpreparationforanimportantmeet-

ing, the representative hasto carry out specic operations such assimulating

the consequencesof this meeting onthe company stockshares. Unfortunately,

beforeheleaveshisocethistimehedidnotdownloadtheappropriatesoftware

applicationsintohisPDA.Consequently,hedecidestoproceedasfollows.First,

hesendsa"wireless"requesttothecompanyserver.Accordingtotheworkload

oftheserver,one ofthefollowingsituationsoccurs.

Servernot"busy"-itacceptstherequestandprocessesit.Tothis end,the

representativehas to send "wirelessly" the requireddata. Later on, the server

transmits"wirelessly"resultstotherepresentative'sPDA.Iftherepresentative

has known before that the server was not busy, he could have attached the

requireddatato therequesthe submittedin thersttime. Unfortunately, this

isdiculttopredict.

Server"busy"- itsuggeststwoalternativestothe representative.Therst

oneistoputhisrequestinawaitinglist.Thesecondoneistosendtherequired

applicationstohisPDAforexecution.Theseapplicationstransferhastofollow

whereawirelessdevicewillbeactingasacomputingplatformtotheapplications

tobereceivedfromtheserver.Weconsiderthese applicationsasm-services.

3 Background

MobileComputingreferstosystemsinwhichcomputationalcomponents,either

hardwareorsoftware,changelocationsinaphysicalenvironment.Movingfroma

locationtoanotherisduetoseveralreasons:componentminiaturization,wireless

networks,and mobile-code programming languages.Kinds of mobile work are

as follows[15]: hardwaremobility,softwaremobility,and combinedmobility. A

codethatisdownloadedfromawebsitetoauser'smobilephonecombinesboth

hardwareandsoftwaremobility.

E-serviceisanapplication componentprovidedbyanorganizationin order

to beassembled and re-usedin adistributed,Internet-basedenvironment [12].

A component is considered asan e-service ifit is: 1) independent as much as

possiblefromspecicplatformsandcomputingparadigms;2)developedmainly

forinter-organizationalsituationsratherthanforintra-organizationalsituations

only;and3)easily composablewithothere-services.

4 System of m-services

4.1 M-services

Therationaleofdesigninganddevelopingm-services 2

istooernewopportuni-

tiestowirelessdevices-orientedusers.Ithappensthattheseuserspostponetheir

operations because they lackappropriate facilitieson their devices. Therefore,

it becomes importantto support such usersbyallowing them:1) to search for

additional facilities, when needed, 2) to fetch these facilities to their wireless

devices,and3) toconducttheoperations1)and2)in atransparentway.A so-

lutionto1)consistsofcreatingbrokeringmechanisms.Asolutionto2)consists

of using wirelesscommunicationmechanisms.Finally, asolutionto 3) consists

ofusingSoftwareAgents(SAs)[6].

Weconsideranapplicationcomponentasanm-serviceifitis:transportable

throughwirelessnetworks;exibleintermofcompositionwithotherm-services;

adaptableaccordingtothewirelessdevices'computingcharacteristics;andexe-

cutable onwirelessdevices.

4.2 Architecture

In our work,brokeringmechanisms and SAs are considered in the design and

development of asystem oeringm-services to wireless devices-orientedusers.

Thissystem'sfeaturesare:

2

Thersttypeis associated withusersof m-services. Thesecond andthird

typesareassociatedwithprovidersofm-services.

Createasoftwareplatform,calledMeetingInfrastructure(MI),that willbe

headedbyasupervisor-agent.This MIhasabrokeringrole[10].

Develop twotypes of delegates: provider-delegate and user-delegate. Dele-

gates interact respectivelyon behalf of user-agents and provider-agentsin

theMI.

Developstorage serversthat savethe sequence of m-services to be sent to

wireless devices for execution. Storage servers are spread across networks

andstorage-agentsareresponsibleofthem.

Figure1illustratesthearchitectureofoursystem.Itisdecomposedintofour

parts:user, provider, MI,and storage.The MI andstorageparts are linked to

theuserpartinawirelessway.Meanwhile,theMIandstoragepartsarelinked

totheprovider-partin awiredway.

Meeting infrastructure User

delegate

Provider delegate Interactions Wireless

Interactions Interactions

User User-agent

Provider-agent Device-agent Supervisor

agent

Bank of m-services

Provider Storage

server ₁

Storage server _j Storage

server _i

M-services M-services

Requests Notification Storage-agent ₁

Wireless connection Wired connection

Figure1.Architectureofm-servicessystem

The user part consists of users and user-agents.User-agents act on behalf

ofusers; theyaccepttheirneeds, convert theminto requests,and submitthem

to user-delegates. The MI supervisor creates user-delegates. To satisfy users'

requests,user-delegatesinteractwithprovider-delegates.

The provider-part consists of providers,provider-agents,and device-agents.

Provider-agentsactonbehalfofprovidersofm-services;theyadvertisetheirm-

servicestouser-delegates,throughprovider-delegates.Inaddition,theymonitor

the behaviorof providersin caseof new m-services are oered,and thus need

to be announced. In Figure 1, m-services are gathered into a bank on which

provider-agentsanddevice-agentsarelocated.Provider-agentscreateprovider-

less devices for execution.The rationaleof havingdevice-agents is to consider

the dierences that exist between wireless devices, e.g. screen dimension and

processorspeed.

The MI part is a software platform on which user-delegates and provider-

delegatesinteractinalocalandsecureenvironment[9].Inanopenenvironment,

mostoftheinteractionsbetweenrequestersofservicesandprovidersofservices

are conducted through third parties, known asbrokers.Despite its important

role, abrokercouldeasily becomeabottleneck. Toovercomethis problem,re-

questers and providers may have to bypass the broker. They need a common

environment in which they meet and interact directly. The MI plays the role

ofthisenvironment.Inoursystem,theMIsupervisor-agenthasseveralrespon-

sibilities, among them: it monitorsthe interactions that occur within the MI;

it makesthe MI a safeenvironment; and it directs user-delegatestowardsthe

provider-delegatesthatinterestthem.

Thestoragepartreceivesthesequenceofm-servicesthatwillbesenttousers

forexecution.Accordingtooursystemexecution'sprinciples,m-servicesaresent

toauser'swirelessdeviceonebyone.Severaladvantagesareobtainedfromthe

useofstorage-servers.Auser-agentdoesnothavetodealwithseveralproviders.

Its point of contact for getting the m-services is the storage-agent.The same

thing applies to device-agentsthat will be interacting with few storage-agents

insteadofseveraluser-agents.Securityisincreasedforbothusersandproviders.

Storage-serversareindependentplatformswheresecuritycontrolareconducted.

4.3 Software agents

User-oriented components User-agent resides in a wireless device. First,

the user communicates with his user-agent to arrange requests. After submit-

ting them to the user-delegate, the user-agent goes into a standby mode and

waits for notications from its delegate. Notications concern the sequence of

m-servicesthatsatisestheuser'srequests.Beforeexecutingthemonuser'sde-

vice,m-servicesareputinastorageserver.TheMIsupervisor-agentsuggeststo

user-delegatethestorageserverto beused consideringforexampletheserver's

location. To downloadthe m-servicesone at atime from thestorageserverto

theuser'swirelessdevice, theuser-agentcommunicates withthestorage-agent.

Theuser-agentkeepstrackof theexecution ofan m-service,before itasks the

storage-agenttosubmitthenextm-service.Whenitisreceived,theexecutedser-

viceisdeletedfromthewirelessdeviceplatform.Finally,theuser-agentinforms

theuseraboutthecompletedrequests.

If this is the rst time that a user-agentsubmits requests, the supervisor-

agent creates a user-delegate in the MI to be associated with that user-agent

(cf. Table 1). For the nextrequests, the user-agentinteracts directly with the

user-delegate (cf. Table 2). Table 1 and Table 2 use "submit", "reply", and

"notify"performativesillustratingtheinteractionsthattakeplacebetweenuser-

agents and supervisor-agent and between user-agents and delegate-agents. In

considersthesecharacteristicsinitsprocessofwrappingm-services.InTable2,

"submit" performative occurs once a user-agent knows the delegate-agent to

whichithasbeenassociated.

Table1.Interactionsuser-agent/supervisor-agent

Submit(Id-submit: id1, From: user-agent1, To: supervisor-agent1, Content:

request

1

,Device:(Brand:brand

1

,Type:type

1

,Screendim.:dim

1 ))

Reply(Id-reply:id

1

,From:supervisor-agent

1

,To:user-agent

1

(In-reply-to:id

1 ),

Delegate: (Id: user-delegate1, Contact: user-delegate1@...), Storage-server: (Id:

storage-agent1,Contact:storage-agent1@...))

Table2.Interactionsuser-agent/user-delegate

Submit(Id-submit:id2,From:user-agent1,To:user-delegate1,Content:request2,

Device:())

Notify(Id-notify: id

1

, From: user-delegate

1

, To: user-agent

1

(In-reply-to: id

2 ),

Content:sequence1/m-service1;2)

User-delegate resides in the MI, acting on behalf of user-agent. The user-

delegate receives the user's requests from the user-agent (cf. Table 2). After-

wards,it interacts with provider-delegates. The purpose isto match user'sre-

questswithproviders'm-services.Incasethereisamatch(weassumethatthere

is alwaysamatch), the user-delegate designsthe sequence ofm-services to be

included in satisfying the user's requests. Information about this sequence is

senttothestorage-agent(cf.Table3).Thepurposeistomakethestorage-agent

ready to receivem-services from device-agents.Furthermore,theuser-delegate

notiestheuser-agentaboutthesequenceofm-servicesithasestablished(cf.Ta-

ble2). InTable3,tworelevanteldsof"to-get-ready"performativeareimpor-

tant."Destination"eldcorrespondstotheuser-agentforwhichthesequenceof

m-services hasbeendesigned. "M-services"eld correspondsto the m-services

thedevice-agenthasto submit. Toset upasequence, thestorage-agentknows

them-service that comesbefore andafter them-services tobesubmittedbya

device-agent. Instead of creating auser-delegate on awireless-device platform

and shippingitto theMI, wesuggestedtoundertakethisoperation in theMI

for twomain reasons:evenifweexpect abigimprovementin wireless devices'

resources,thoseresourceshavetobeusedina"rationale"way;andthewireless

connectionthattransferstheuser-delegateisavoided.

Provider-orientedcomponents Provider-agentresidesinprovider'ssite,run-

To-get-ready(Id-to-get-ready:id4,From:user-delegate1,To:storage-agent1,Se-

quence:sequence

1

,Destination:user-agent

1

@...,M-services:(From:device-agent

i ,

Before:0[m-serviceh]1,Id:1[m-servicei]n,After:0[m-servicej]1))

Provider-delegatesbroadcastm-servicesto user-agents,throughuser-delegates.

Theprovider-agentisinconstantinteractionswithitsprovider-delegate(cf.Ta-

ble 4). For instance: it communicates to the provider-delegate the negotiation

strategyithastofollowwithuser-delegates.

Table4.Interactionsprovider-agent/provider-delegate

Submit(Id-submit:id6,From:provider-agent1,To:provider-delegate1,Content:

strategy

6

/m-service

6

,Device:())

Inform(Id-inform:id1,From:provider-delegate1,To:provider-agent1,Agreement:

(Sequence: sequence1, With: user-agent1, Service: 1[Id: m-servicei]n), Storage-

server:(Id:storage-agent

1

,Contact:storage-agent

1

@...),Device:(Brand:brand

1 ,

Type:type1,Screendim.:dim1))

Device-agentresidesinprovider'ssite.Itsresponsibilityistowrapm-services

accordingtothedevicestowhichtheywillbesentforexecution.Initially,these

m-servicesaresenttostorageservers.Theprovider-agenthasalreadysubmitted

the contact details of the storage-server to the device agent. We recall that

the user-delegate hasinformed the storage-agentof that storage server about

them-servicesitwillreceive(cf.Table3).Double-checkingtheinformationthat

user-delegatesandprovider-delegatesforwardtoastorage-agentguaranteesmore

securitytooursystem.

Provider-delegateresidesintheMI;itactsonbehalfofprovider-agent.Inour

system,theprovider-delegateisresponsibleforinteracting withuser-delegates,

regarding the m-services it oers. In addition, it interacts with its provider-

agentfornoticationpurposes.Noticationsarethenforwardedtodevice-agent

forconsideration.Werecallthat theprovider-agentcreatesaprovider-delegate

andtransfersitto theMI.

MI-oriented components Supervisor-agent resides in the MI and has sev-

eral responsibilities:it supervises theoperationsthat occurintheMI; itmedi-

atesincaseofconictsbetweenuser-delegatesandprovider-delegates;itsets-up

user-delegatesandassignsthemtouser-agents(cf.Table1); itchecksprovider-

delegatesidentitywhentheyarrivefromprovidersites;and itsuggeststouser-

delegatesthestorageservertobeused.

The purpose of such a server is to save the m-services to be sent to wireless

devicesforexecution.Accordingtotheinformationonthesequenceofm-services

ithasreceivedfromtheuser-delegate(cf. Table3,"before"and"after"elds),

the user-delegate arranges the sequence as the m-services start arriving from

providers.As soonas this sequence is completed,it informsthe user-agentin

orderto getprepared(cf.Table5).

Table5.Interactionsdevice-agent/user-agent

Get-prepared(Id-get-prepared: id

7

,From: storage-agent

1

, To: user-agent

1 , Se-

quence:sequence1,Status:ready)

Basedonthe requestsit receivesfrom user-agent,thestorage-agentpushes

them-servicesoneatatime(cf.Table6).Thesem-servicesarereadyforexecu-

tion.Thedeletionofm-servicesfromthestorage-serversaswellasfromwireless

devicesfollowsspecicreliabilityrules(cf.Figure 3).

Table6.Interactionsuser-agent/storage-agent

Request(Id-request: id

24

, From: user-agent

1

, To: storage-agent

1

, Sequence:

sequence1,M-service:?m-service1)

Push(Id-push:id1,From:storage-agent1,To:user-agent1 (In-reply-to:id24),Al-

readysubmitted:3,Remained:2,Attachment:m-service1)

4.4 Operating mode

Theoperatingmodeofoursystemconsistsofvestages:agentication,identi-

cation,correspondence,notication,andrealization(cf.Figure2).

Agentication stage purpose is to set up the dierent infrastructures and

agentsthatconstituteoursystem.User-agentsareestablishedat theuserlevel.

Provider-agentsanddevice-agentsareestablishedattheproviderlevel.Lastbut

notleast,themeetinginfrastructureandstorageservers,includingtheirstorage-

agents,arecreated.

Identication stage purpose is toinform theMI supervisor-agentaboutthe

existenceofusersandproviderswhoareinterestedin oursystem.Attheagen-

ticationstage,user-agentsandprovider-agentsarerespectivelyinstalledontop

of users' wireless devices and providers' resources.The outcome of the identi-

cation stage is the creation of user-delegates and the reception of provider-

delegates coming from provider-sites.Creation and receptionoccur in the MI.

Provider-agents inform the supervisor-agent about their readiness to submit

their provider-delegates to the MI. User-agents inform the supervisor-agent

Meeting infrastructure

3. Interactions User

User-agent Supervisor-agent

Bank of m-services

Provider Storage

server ₁ Storage-agent ₁

2.a Creation

2.b Migration 1.a Needs

User-delegate Provider-delegate

Device-agent Provider

delegate Provider-agent 1.b Creation

4.a M-services

notifcation 4.b Contracts

notifcation 5. Contracts notification 6. M-services

transfer 7. M-services

transfer for execution

Figure2.Operatingofm-servicessystem

Correspondence stage purpose is to enable user-delegates and provider-

delegates toget together.User-delegateshaverequeststo satisfyand provider-

delegateshaveservicestooer.First,auser-delegatesearchesfortheprovider-

delegates that have the services it needs. Two approaches exist (cf. Table 7

and Table 8): a/ The user-delegate asks the supervisor-agent to suggest a

list of provider-delegates that havethe services itneeds. Here, thesupervisor-

agentplaystherole ofarecommender.b/Theuser-delegaterequestsfrom the

supervisor-agent the contact details of all the provider-delegates that exist in

theMI.Table8liststheadvantagesanddisadvantagesof bothapproaches.

Table7.Interactionsuser-delegate/supervisor-agent

Ask-for(Id-ask-for:id32,From:user-delegate11,To:supervisor-agent1,Content:

1[service

i

,?provider

i ]n)

Recommend(Id-recommend:id

1

, From: supervisor-agent

1

, To:user-delegate1

1

(In-reply-to:id32),Content:a/Provider-delegate1;4 b/Provider-delegates)

Independentlyoftheapproachofsearchingfordelegate-providers,theuser-

delegate submits its needs of services to selected provider-delegates after in-

teractions. Basedondierent parameters,such asworkloadandcommitments,

provider-delegatesanswerthe user-delegate. At this stage of our work,we as-

sumethat providersdonothaveservicesincommon.Consequently,thereisno

need for a user-delegate to look for the best service (negotiation for a service

is1userwith1provider) 3

.Oncetheuser-delegateandprovider-delegatesagree

3

Thisisnota shortcomingof oursystem.Itis partofour currentworkto consider

Advantages Disadvantages

a/ a/

Provider-delegatesaretargetedinadvance.Supervisor-agentbecomesabottleneck.

Less interaction messages between user-

delegates andprovider-delegates.

Supervisor-agent'srecommendationscould

notsatisfycompletelyuser-delegates.

User-delegateshaveanarrowperceptionof

theMIcontent.

b/ b/

User-delegates have a wide perception of

theMIcontent.

Moremessagestodiscoverwhatprovider-

delegatesoer.

Morefreedomisgiventouser-delegates.

uponthem-servicestouse,noticationsaresenttodierentrecipients.Thiswill

beexplainedin thenoticationstage.

Notication stagepurposeistoinformdierentagentsaboutuser-delegates'

andprovider-delegates'agreements.

Regardingthe user-delegate, it is in charge of the following operations:in-

formstheuser-agentaboutthesequenceofm-servicesithasestablishedtosatisfy

itsuser'srequest(cf.Table2);andinformsthestorage-agentaboutthesequence

ofservicesitwillreceivefromdierentdevice-agents(cf.Table3).

Regarding the provider-delegate, it noties the provider-agent about its

agreements with a user-delegate (cf. Table 4). We recall that provider-agents

donotreject anyagreements.

Based on the information it has received from its provider-delegate, the

provider-agent forwards them to the device-agent. This information concerns

them-servicesthat areinvolvedandthestorage-serverthatisused. Amongthe

actions the device-agent undertakes we cite submitting the m-services to the

storage-agentofthestorage-server.

Realization stage purpose isto executethe sequenceof m-services that the

user-delegate has designed. User-agent and storage-agent are the participants

ofthisstage.Werecallthattheuser-delegatehasalreadyinformedthestorage-

agentaboutthem-servicesitwillreceivefromdevice-agents(cf.Table3).Before

theuser-agentstartsaskingthestorage-agentforthem-servicesithas,itwaits

foranoticationmessagefrom thestorage-agentmentioningthatthesequence

isreadytobesubmittedforexecution.

Intherealization phase,reliabilityaspecthasbeentakeninto account.Our

approachconsidersastorage-serverasabackupserverforthem-services.When

astorage-agentsendsanm-servicetoauser-agent,thestorage-agentkeepsacopy

ofthisserviceatitslevel.Itdeletesitwhentheuser-agentasksforthem-service

that follows the one it has received. For the last m-service of a sequence, the

user-agentsendsanacknowledgementmessagetothestorage-agentsoitdeletes

User-agent Storage-agent

Actions Actions

Interactions Sequence: m-service _1,2,3

Request: ?m-service ₁

save: m-service ₁ Push: m-service ₁

run: m-service ₁

Request: ?m-service ₂

delete: m-service ₁ Push: m-service ₂

wait: m-service ₂

Request: ?m-service ₂ Push: m-service ₂ run: m-service ₂

Request: ?m-service ₃

delete: m-service ₂ save: m-service ₂

Push: m-service ₃ run: m-service ₃

Request: ok

delete: m-service ₃ save: m-service ₃ prepare: request

To-make-ready: seq. ₁ prepare: message

delete: m-service ₁

delete: m-service ₂

delete: m-service ₃

Figure3.Interactiondiagramofrealizationphase

5 Implementation

An implementation of the MI has already been undertaken in [9]. The proto-

typeusesSUN'sJavaSpacestechnology[5]toimplementarepositorythatholds

providers'm-servicesadvertisement.JavaSpacesis animplementationofLinda

[8]thatprovidesasimple,fast,andauniedmechanismforsharing,coordinat-

ing, and communicatingdistributed resources, services,and objectsacrossthe

network.

TheMIisimplementedasasetofthreemodules.Therstmoduleistheman-

agementandinstallation,whichisresponsibleforreceivingdelegatesfromtheir

originalsystemsandinstallingthem.Allthesecurityoperationsareundertaken

in thismodule.Thesecondmodule istheinteractionmodulethat supportsthe

communicationsthat takeplace betweenuser-delegatesandprovider-delegates.

Finally, the third module is the advertisement and consulting module, which

is supportedby JavaSpaces,dealswith advertising servicesandidentifying the

servicesthatarerequiredforsatisfyingspecicneeds.Inaddition,theadvertise-

mentandconsultingmodulesupportsthesubscriptionprocesstouser-delegates.

Forinstance,if auser-delegatesisinterestedin aspecic event, thenit canbe

notiedwhenthiseventoccurs.JavaSpacesprovidesthisnoticationoperation.

Provider-agentsandtheir delegatesanduser-delegates areimplementedus-

ingVoyager[14]. Regardingtheuser-agent,it ismainlyaninterface-agentthat

feedstheuser-delegatewithrequests.ThisagentisimplementedusingJ2ME[4],

whichisaJavaeditionthatrunsonwirelesshandhelddeviceswithconstrained

resources.Asnapshotoftheuser-agentprototypeisshowninFigure4.

Atthisstage ofourimplementation, wesimulatethesituationwhere auser

can enter the m-services he requires.In this example, the useris requesting a

m-service hasbeendownloadedthe userwillbenotied,asshownin Figure4,

sothatshecanstartusingitasshowninFigure5.

Figure5.M-serviceexecutionscreenmockup

6 Related work

There exist several projectsthat study howwireless devices could change our

wayofdoingbusiness[1,10,11,13].InHPLaboratories,[10]workedondelivering

Internet servicesto wireless users.This work wasconducted under the project

for PervasiveServices Infrastructure(PSI). The vision is "any service to

anyclient(anytime, anywhere)".Theprojectinvestigatedhowooading parts

ofapplicationstomid-pointserverscanenableandenhanceserviceexecutionon

aresource-constraineddevice.Inourwork,weareinterestedin thesameissues.

Furthermore,weareinterestedinsupportingusersintheirsearchform-services

in an open environment. In [11] the Odyssey project provides systemsupport

for mobileand adaptiveapplications. Itdenes aplatformfor adaptivemobile

data access on which dierent applications, such as a web browser, a video

player, and a speech recognition, could run on top. The Odyssey's approach

is to adjust the quality of accessed data to match available resources. In our

system,weconsideredadaptabilityattwodierentlevels:m-servicesarewrapped

according to the wireless devices' characteristics; and user-agents request m-

services from storage agents according to the resources that are available on

typesofrobustandscalabledistributedInternetservices.Ninja'sobjectiveisto

meet therequirementsofanemergingclass ofextremelyheterogeneousdevices

that would access these services in atransparent way. In Ninja, the proposed

architecture considered four elements: bases, units, active proxies, and paths.

Comparable to our sequence of m-services, a path is an abstraction through

whichunits,services,andactiveproxiesarecomposed.Proxiesaretransforma-

tionalintermediariesputbetweendevicesandservicestoshieldthemfromeach

other.Ninjaproxiesaresimilartoourdevice-agents.Inaddition,Ninjasuggested

aServiceDiscoveryService (SDS) fortworeasons:enableservicesto announce

theirpresenceandenableusersandprogramstolocatetheseannouncedservices.

SimilartotheSDS,theMIhasabrokeringrole.Moreover,theMIfacilitatesthe

directinteractionsbetweenprovidersandusers.Infact,theMIavoidsbottleneck

situationsandensuresabettersecurity.

7 Conclusion

In this paper, wepresentedour work on m-services. M-servicesare considered

as an extension to e-services. Usersare moreand more relyingon their wire-

lessdevices to completetheir dailyoperations. Therefore,newfacilitiesshould

be provided. Our work aims at achieving"anywhere and anytime" paradigm.

This paradigmcould be summarized by[2] whostated "How tomake a set of

heterogeneousservicesimplementedandprovidedbydierentprovidersavailable

for roamingusers asanintegratedpackage,withthesame"look andfeel"across

dierent networks,andfromdierentterminals".

Several aspects are still under investigation, among them security [7] and

scalability. Oursuggestion forsecurity consists of enhancingthe storage-agent

with securitymechanismsthat couldbegeneric; in thesense that these mech-

anisms will beapplied to all m-services despite their origin (i.e.device-agent)

and destination (i.e.user-agent).Specic security proceduresthat answereach

user'sprioritiesshouldbedoneat thewirelessdevice level.Since theresources

onwirelessdevicesshouldbeusedinarationaleway,ourfutureworkisbasedon

trustbetweenuser-agentsandstorage-agents.Forinstance,if auser-agenthad

theopportunitytodealwiththesamestorage-agentseveraltimesandbasedon

its previous experiences, the user-agentcould entrustto this storage-agentits

specicsecurityprocedures.

Regardingscalability,thearchitectureofthem-servicessystemwesuggested

inFigure1ishighlyscalable.Thesystemcanbeextended,atareasonablecost,

asthedemandforthem-servicesitprovidesincreases.Thiscanbeachievedby

addingmoremeetinginfrastructurestoawirelesscarriernetwork.Thebankof

m-services and the storage-serverscan be replicated across the network. This

allowsustoavoidtheperformancebottleneckthatwouldariseifasingleMIhas

1. S. Case, N. Azarmi, M. Thint, and T. Ohtani. Enhancing e-communities with

agent-basedsystems. IEEEComputer,July2001.

2. L. Esmahi,R.Impey,andR.Liscano. Anarchitecturefor providingmobileinte-

gratedservicesforroamingusers. InProceedingsProceedings ofMICON,Ottawa,

2000.

3. M.C.Fauvet,M.Dumas,B.Benatallah,andH.Paik.Peer-to-peertracedexecution

ofcompositeservices.InProceedingsoftheInternationalWorkshoponTechnologies

forE-Services(TES'2001)heldinconjunctionwithVLDB'2001,Italy,2001.

4. J2ME. http://java.sun.com/j2me,VisitedNov.2001.

5. JavaSpaces. http://java.sun.com/products/javaspacesl,VisitedNov.2001.

6. N. Jennings, K.Sycara, and M. Wooldridge. A roadmap of agent research and

development. AutonomousAgents andMulti-AgentSystems,1(1),1998.

7. S. Key Miller. Facing the challenge of wireless security. IEEE Computer, July

2001.

8. Linda. http://www.cs.yale.edu/Linda/linda.html,VisitedNov.2001.

9. Z. Maamar, E. Dorion, and C. Daigle. Towards virtual marketplaces for e-

commerce. CommunicationsoftheACM,44(12),December2001.

10. D.Milojicic,A.Messer,p.Bernadat,I.Greenberg,G.Fu,O.Spinczyk,D.Beuche,

and w.Schroder-Preikschart. -pervasiveservicesinfrastructure. Technical re-

port, HPTechnicalReportHPL-2001-87,HPLaboratoriesPalo Alto,2001.

11. B.D. Noble, M. Satyanarayanan, D. Narayanan, J.E. Tilton, J. Flinn,and K.R.

Walker. Agileapplication-awareadaptationormobility.InProceedingsofthe16th

ACMSymposiumonOperatingSystemsPrinciples,France,1997.

12. B.PerniciandM.Mecella. Designingcomponentsfore-services. InProceedingsof

the VLDB Workshop on Technologies for E-Services (VLDB-TES 2000), Egypt,

2000.

13. TheNinjaproject. http://ninja.cs.berkeley.edu,VisitedSeptember2001.

14. Voyager. http://www.objectspace.com/products/voyager,VisitedNov.2001.

15. A. I.Wand and L. Chunnian. Process supportfor mobileworkacross heteroge-

neoussystems. Technicalreport,Departmentof InformationScience,Norwegian

UniversityofScienceandTechnology,Norway,2001.