Enabling Technologies for Wireless E-Business phần 6 doc

190 B. Yang and J. Li u f itness value an a g ent has, the more ph e romone it will release. When a g ents move to a crossroad, they w ill preferentially select the path with a denser concentration of pheromone. A group of mobile ag e nts will solve the DOPS collectively through a positive feedback mechanism: agents that can find o p timal s olutions will have a hi g h er f i tness va l ue; t h e i r routes w ill h ave d enser p h eromone l eve l s, attract i ng more a g ents to c h oose t h em; an d b a d a g ents w i t h a l ower f i t n e ss va l ue w ill a dj ust t h e i r di rect i on of trave l ( or ot h er b e h av i ors ) by fo ll ow i n g t h e g oo d a g ents. Eventu- all y , after a period of evolution controlled b y positive feedback, the entire s y stem will reach an equilibrium state correspondin g to the desired optimal solution. In this model, chan g es to a g ents’ fitness value embod y their self-adaptive behav- i ors as single entities, while the positive feedback system embodies the self- organized behaviors of multiple agents. 8.5 Security Wi t h co d e m ig rat i on, t h e mo bil e a g ent para dig m b r i n g s i ncrease d performance an d f l ex ibili t y to di str ib ute d s y stems. On t h e ot h er h an d , t h e a bili t y to move i n i tse l f b r i n g s s ig n i f i cant secur i t y t h reats, to b ot h a g ents an d h osts. On ly a perfec t s olution to these serious securit y problems would enable the mobile a g ent para- di g m to become the mainstream software technique for constructin g lar g e-scale distributed commercial a pp lications. 8.5.1 Issues and C ountermeasures T wo main types of threat need to be a d d ressed: agent-to-syst e m and system-to- agent attacks. Jansen et al. [27] present a good survey of the threats faced by the mobile agent paradigm and the corresponding countermeasures. Th e agent-to-system category i nc l u d es t h e ki n d of t h reats i n w h i c h agents ex - pl o i t secur i ty wea k nesses to attac k an agent system. T h i s group ma i n l y compr i ses masquera di ng, d en i a l of serv i ce, an d unaut h or i ze d access. Converse l y, t h e system- to-a g ent cate g or y includes threats in which s y stems attack a g ents that are situated within them. A g ain, masqueradin g and denial of service form part of this g roup, as additionall y do eavesdroppin g and alteration. Many conventional security techniques used in traditional distributed a pp lica- t ions such as identity authenticati o n, encryption, integrity verification, authoriza - t ion, access control, and so on are also useful as countermeasures within the mo bil e agent para di gm. T h ere are a l so severa l e xtens i ons to th ese convent i ona l t ec h n i ques an d new met h o d s d ev i se d spec i f i ca ll y to con t ro l mo bil e agent secur i ty. J ansen et a l . [27] surve y some recent ly d eve l ope d secur i t y tec h n i ques. Counter - measures a i me d at p l atform protect i on i nc l u d e software- b ase d fau l t i so l at i on, safe co d e i nterpretat i on, s ig ne d co d e, aut h or i zat i on, an d attr ib ute cert i f i cates, state ap- p raisal, p ath histories, and p roof carrying code. Countermeasures f or agent protec- t ion include p artial result enca p sulation, mutual itinerary recording, itinerary 8 Mo bil e Agents: T h e State of t h e Art 191 recordin g with replication and votin g , execution tracin g , environmental ke y g en- e ration, computing with encrypted functions, and obfuscated code. 8.5.2 Fac i l i ty In this section we p resent a con c rete mobile agen t s ecurity facility (MASF), which we have ourselves develo p ed, in orde r to illustrate some of the threats and coun- f termeasures di scusse d ear li er from a more pra c t i ca l an d i mp l ementat i on-or i ente d p o i nt of v i ew [28]. I ssues T he securit y threats that ma y occur over the whole lifec y cle of a mobile a g ent come from both malicious a g ents and the hosts to which a g ents mi g rate. Malicious mobile a g ents ma y access and modif y data to which the y should not have access or attem p t to interfere with t h e execution of their hosts. The p otential threats, fro m both the agent and host points of view, can be: • Be f ore mi g ration. T h reat A: Dur i n g mo bil e a g ent st o ra g e, t h e repos i tor y m igh t b e i nva d e d an d t h e co d e or c l ass for t h e mo bil e a g ent c h an g e d b efore i n i t i at i on. • D urin g mi g ration. T hreat B1: When a mobile a g ent mi g rates across net - w orks are not controlled b y sender or receiver, while in possession of confi- d ential data, disclosure of this informati o n cou l d be fatal . Thr e at B2 : Th e execution logic of the mobile agent might also be changed by the interrupter, w hich might cause damage to the destination host. • After migration. T hreat C1: the supposed “destination” might in fact be a counterfe i t, create d b y a b us i ness r i va l to stea l i mportant i nformat i on b e i ng carr i e d b y t h e mo bil e agent. T h reat C2: even i f t h e d est i nat i on i s correct, t h e agent may st ill b e d ece i ve d b y a ma li c i ous h ost. For examp l e, i t m i g h t not r eceive the contracted services or resources, or mi g ht even be maliciousl y changed before going for another hop. Threa t C3: At the same time, the land- a a in g host of the mobile a g e nt s h ou l d al so be su r e t h at th e in co m e r i s fr o m th e correct service contractor and will not cause it any damage. Threat C4: even if the mobile agent does come from the correct peer, the host still needs to keep itself informed about its behavior in case the agent does something tha t goes b eyon d i ts contract or i ts r i g h ts on t h e system. C ountermeasures T o a dd ress suc h t h reats, a MASF must prov id e t h e fo ll ow i ng features: • A uthentication . This involves checkin g whether o r not an a g ent comes fro m a trustworth y source. This can involve a s k in g for the authentication details to b e sent from the site where the mobile agent was launched or from which i t last migrated. At the same t ime, authentication also e n ables the mobile agent to be aware of the real identity of the receiver, which should be the prope r 192 B. Yan g an d J. L iu service level a g reement (SLA) contractor. Authentication is mainl y used to solve threats C1 and C3 as described earlier. It can also be used to check o n users who want to access the mobile agent repository, which also involves threat A. • Confidentiality. Wh en a mo bil e agent tra n sports conf id ent i a l d ata, t h e transm i tte d a g ent must b e encr y pte d w hil e i n trans i t. T hi s ma k es i t use l ess to a n y h ost, w hi c h d oes not k now h ow to d ecr y pt i t ( w hi c h s h ou ld on ly b e t h e designated server). Confidentiality, im plemented by encryption/decryption, m m c an co p e with the p otential data disclosure of threat B1, and can p revent the r epositor y from attack (threat A). • Integrity . O n reception, the mobile agent must be checked against any m odification or corru p tion due to netw o rk transmission errors or intentional i nvas i on. If t h e i ntegr i ty c h ec k fa il s, t h e rece i ver can as k t h e c li ent to repeat t h e transm i ss i on. T hi s can protect t h emo bil e agent from t h e co d e mo di f i ca- t i on attac k out li ne d i n t h reat B2. • A utho r i z ation. This determines the mobile a g ent’s access permissions to h ost resources. It is intended to p r o t ec t th ose r esou r ces fr o m u na u th o riz ed or o verused access. It indicates, for example, how man y times a resource can be a ccessed or how much it can be used, and what type of access the agent can p erform. For instance, one agent on b e half of a network administrator may b e able to read, write, and modify a given resource and have unlimited access to i t, w hil st anot h er age n t represent i ng a norma l u s er may on l y b e a bl e to r ea d t h e resource an d access i t a li m i te d num b er of t i mes. Aut h or i zat i on mainly deals with the runtime actions of the mobile agen f t . Usua ll y t hi s i s a chieved throu g h an access control polic y that g rants access to s y stem r esources based u p on different levels of trust. Authorization, empowered b y a ccess control, can defeat threat C4. • L ogging. This is a mechanism to keep track of any e v e nts relevant to secu - r ity, such as an agent trying to access system resources or the system itself, a s well as authentication failures. These e vents should be logged to a file fo r l ater ana l ys i s. Logg i ng can, to some d egree, d etect an d t h erefore prevent a m o bil e agent b e i ng d ece i ve d b y t h e h ost, as d escr ib e d i n t h reat C2. Ar c hit ec t u r e T he im p lementation of these features, for the p rotection of both mobile a g ent an d host, is achieved in the MASF, the arc h itecture of which is illustrated as Fi g . 8.6. MASF architecture is functionall y divide d i nto two la y ers, the h i g her bein g a f unction layer and the lower a base service layer. The components or services in the latter are common function a l ities used by the former. Obviously, many services of the function layer depen f d on cryptographic func- t i ons b ase d on e i t h er symmetr i c or asymmetr i c k eys to encrypt /d ecrypt an d s i gn d ata. T h erefore , MASF h as a cryptograp h y lib rary i nteg r ate d i n i ts b ase serv i ce l ayer. data inte g rit y and authentication services, usin g di g ital si g natures. The authentica - T he ke y mana g ement service enables users to administer their own p ublic/ p rivate ke y pairs and associate d ce rtifi c at es f o r use in se lf-a u th e nti c ati o n o r 8 Mo bil e A g ents: T h e State of t h e Art 193 tion information includes both a se q uence (chain) of X.509 certificates, and an associated private key, which is usually referenced as “alias”. T o achieve security, the MASF framework supports flexible security policies to g overn the interactions of agents with each other and with the available resources i n t h e execut i on s i tes. T hi s fun c t i on i s i mp l emente d b yt h e po li cy managemen t s erv i ce i n t h e b ase serv i ce l ayer. T h e d ef i n i t i o n an d enforcement of appropr i ate s ecur i ty po li c i es can on l y procee d after a prec i se id ent i f i cat i on of t h e pr i nc i pa l s ( i.e., the roles that can be authenticated). Securit y lo gg in g service fulfils the lo gg in g requirement mentioned earlier. Althou g h not specific to MASF, the location service is sometimes used b y MASF t o identify the user. W ork f low o f the MA S F A ll t h e mo bil e a g ents’ c l asses or co d es are store d i n digi ta lly s ig ne d arc hi ve f il es. Whenever an administrator, or the software on his or her behalf, wants to fulfill some tasks usin g mobile a g ents, t h e appropriate si g nature must firstl y be verified before access can be g ranted to these a g ents, which are stored in a protected repos i tory. T h e a d m i n i strator t h en s i gns t h e agent to s h ow t h e i n i t i ator, for i n - stance, t h e f i rst agent system. He or s h e can a l so supp l y t h e agent w i t h t h e neces- sar y r igh ts. If a mo bil e a g ent s y stem rece i ves an ag ent from t h e commun i cat i on networ k v i a a g ent transport protoco l ( ATP ) , i t d ecr y pts i t an d tests t h e i nte g r i t y of t h e d ata received b y checkin g the si g nature that the sender has appended. After success - f ull y passin g the inte g rit y check, the next st ep is authentication. The mobile a g en t sy stem verifies the si g nature and certificates attached to this mobile a g ent and o b ta i ns furt h er i nformat i on suc h as w h o wrote i t an d w h o sent i t ( e i t h er or i g i na ll y or from t h e i nterme di ate l ocat i ons ) . T h e in format i on can b e furt h er use d for aut h or i - z at i on an d access contro l . T hi s step w ill i nvo l ve t h e secur i ty d ata b ase. Once aut h ent i cate d , MASF aut h or i zes t h e a g ent, w hi c h means t h at i t attac h es r igh ts to i t or d eterm i nes r igh ts b ase d o n s ecur i t y po li c i es, w hi c h h ave b een d ef i ne d i n a d vance, pro b a bly v i a a SLA. Fig. 8.6. Architecture of mobile agent security facility 194 B. Yan g and J. Li u T he mobile a g ent can then be executed with care of access control to imple - ment its assigned task. When the mobile agent has finis h e d its work and wants to migrate to another location, the system stops the agent’s execution and packs i t with its current state, as normal. Depending on the agent’s task, t h e rights’ adjust - i ng mo d u l e may b e ca ll e d at t hi s moment to a dj ust i ts current r i g h ts, for examp l e, t o i ncrease t h ose to b e grante d at i ts next l ocat i on. N ext, t h e s i gner / encryptor mo d u l e i s ca ll e d b y agency to s i gn t h e mo bil e agen t t o conf i rm t h e execut i on or an y c h an g e o f a g ent. Encr y pt i on ma y a l so b e app li e d by t hi s mo d u l e. F i na lly , a g enc y opens a commun i cat i on c h anne l to t h e tar g et mo bil e a g ent s y s - t em and sends the agent. The channel can be a secure one enhanced by secure socket layer (SSL). 8.6 Summary In t hi s c h apter we h ave b r i ef ly i ntro d uce d t h e concept o f mobile agents and dis- f cusse d some of i ts a d vanta g es an d app li cat i ons. We h ave a l so di scusse d some i mportant tec h no l o gi es requ i re d for t h e d e t ail e d i mp l ementat i on of suc h a s y stem. Althou g h this paradi g m could ease the dev e lopin g , testin g , and deplo y ment o f distributed a pp lications, and could also simplif y the understandin g and sustainin g of such s y stems, there are still man y open issues that need to be resolved perfectl y b efore this can become an industrial software standard ready for commercial applications in the same way as OOP and CORBA. Besides issues such as p lann i ng, communication, p erformance, an d security, as di scusse d ear li er, t h ere i s t h e i mportant qu e st i on of stan d ar di zat i on. O M G MA S IF ( mo bil e agent system i nteropera b ili ty fac ili ty ) [29] an d OMG MAFS ( mo bil e agent fac ili ty spec i f i cat i on ) [11] are goo d i n i t i a l efforts to a dd ress t hi s i ssue. How- e ver, the mobile a g ent co m munit y must take further steps t o develo p an industrial standard for this paradi g m, j ust like the one in use in th e fi e l d o f d i s tri bu t ed o b j ects. Furthermore, technologies and theories of artificial intelligence fields should be i ntegrated into the mobile agent paradig m s o as to enable mo b i le agents to become smarter and more competent in highly complex tasks such as distributed o p timiza- ti on pro bl ems i n tru l y di str ib ute d , l arge-sca l e, open, an d d ynam i c env i ronments suc h as t h e Internet. Fortunate ly , more an d more new tec h n i q ues are now b e i n g exp l ore d , an d curren t wor k i s prom i s i n g enou gh t h at, w i t hi n 10 y ears or even sooner, t h e mo bil e-a g en t p ara dig m w ill b e w id e ly use d i n man y di str ib ute d an d i nte llig ent app li cat i ons, espe- cially in the ubiquitous computing environment. Ubiquitous computing is said to be the third generation of computation after the mainframe and personal computer (PC) eras. In this, the user is surrounded by lots of i nv i s ibl e sma ll computers o r sensors, connected by ad r h oc or w i re l ess networ k s. U bi qu i tous comput i ng ma i n l y a i ms at d eve l op i ng new mo d e l s an d tec h no l og i es to construct t h e u bi qu it ous soc i ety ( U-soc i ety ) , w hi c h can offer anyw h ere an d anyt i me 8 Mo bil e A g ents: T h e State of t h e Art 195 s ervices, delivered throu g h an y devices, as required t o su pp ort an individual’s d aily life. In order to adapt to the dyna m i c re q uirements of different p eo p le, the U -society requires personal information such as profiles, preferences, likes, and habits. Since p eo p le often move around, such p ersonal information has to be sent to t h e current l ocat i on. Bagc i et a l . [30] present two poss ibl e approac h es: e i t h e r t h e user carr i es t h e re l evant i nformat i on on d ev i ces w i t h hi m or h er, or t h e u bi qu i- tous system ta k es care of stor i ng an d sen di ng i t. O b v i ous l y, t h e l atter s i tuat i on, i n w hich a mobile user is alwa y s accompanied b y a ubiquitous a g ent, which serves as a virtual reflection of the user and can p rovide the services, is p referred. E xistin g mobile a g en t s y stems for Internet applicati o ns such as A g let, More, Grasshoppers, and D’Agent are very h e avyweight and are no t suitable for ubi q ui- tous computing. Bagci et al. [30] discuss the re q uirem e nts for the ubiquitous agent p ara di gm: u bi qu i tous agents cou ld use b ot h w i re d an d w i re l ess me di a for commu- n i cat i on an d m i grat i on; t h e system s h ou l d b e p l atform i nd epen d ent, s i nce software an d h ar d ware are h eterogeneous i n t h e U- s oc i ety; agents s h ou l d b e li g h twe i g h t so that the y work not onl y on powerful PCs but also on batter y -operated and mem - or y -restricted PDAs, wearabl e computers, or tin y sensors; a g ents could use dif- f erent access mechanisms and protocols for accessin g information provided b y heterogeneous ubiquitous devices; agents should be context sensitive; and secu - rity, such as privacy protection, i s also an im p ortant re q uirement. M ultiagent teamwork has been widely studied i n the fields of distributed artifi- c i a l i nte lli gence. W i t h t h e emer g e nce of u bi qu i tous comp u t i ng, u bi qu i tous agen t teamwor k b ecomes a new c h a ll enge. T h e ubiquitous agent comm unity (UAC) is a m m p rom i s i ng approac h to t h e organ i zat i on of agents i nto a j o i nt l y funct i on i ng team. Th e s ig n i f i cant aspect of suc h a commun i t y i s t h at i t w ill a l wa y s h ave one g oa l t h at will m o t iv at e an d d r ive i t s m e m be r s t o f ul f ill t hei r i n dividu a l ta sks an d f u n c- t i ons. U A C s w i t h di fferent structures h ave di fferent funct i ons, an d t hese s tr uc t u r es w ill evolve autonomously according to the collective interactions of their mem - b ers. Liu et al. [31] p resent one commu n ity structure, called the ubiquitous agent community for rational competit i on and cooperation in the U-society. A UAC i s essent i a ll y an i nte lli g e nt i nfrastructure t h a t e na bl es agents to l oo k a h ea d to p l an an d d e li ver w h at a user wants. It wor k s j ust lik e a persona l agency. For i nstance , i t can he l p a user to effect i ve ly mana g e te di ous d a ily rout i ne act i v i- t i es suc h as process i n g ema il s, p l ac i n g or d ers, ma ki n g meet i n g arran g ements, d own l oa di n g news, an d so on. A UAC can i n t eract w i t h users i n var i ous wa y s. Fo r i nstance, as a p erson uses a smart hand-held devi c e to enter a subwa y station on the wa y to work, a UAC can seamlessl y upload list of thin g s to be done to that d evice. Alon g with each of the thin g s listed, the information provided b y the UAC can a l so i nc l u d e t h e correspon di ng tas k s requ i re d . T h us, i ns id e t h e mov i ng su b- w ay tra i n, t h e user w ill b e a bl e to go t h roug h eac h of t h e recommen d e d tas k i tems an d furt h er ver i fy an d d e l egate certa i n j o b s, su c h as forwar di ng a report or ma ki ng a meet i n g appo i ntment, to a commun i t y a g ent w i t hi n t h e UAC. Bes id es p l ann i n g an d execut i n g t h e i tems on a ca l en d ar, t h e user can a l so rece i ve ot h er persona li ze d s erv i ces b ase d on hi s or h er prof il e, w hi c h m a y include sports news, urgent emails, a a and specific documents prepared for the da y ’s meetin g s. Fi g ure 8.7 g ives an 196 B. Yan g an d J. L iu i llustrative example of personal services that can be provided b y a communit y o f competing and cooperating agents. F ig. 8.7. Schematic illustrati o n o f an UAC [ 31 ] A UAC conta i ns two types of agents: c-agents an d s-agents. T h e former ma k es tas k p l ans as we ll as contract i ng d ec i s i ons on w h at an d wh ere some tas k s w ill b e carr i e d out, w h ereas t h e l atter performs t h e d e l egate d tas k s. A c -agent carr i es ou t s uc h funct i ons as tas k p l ann i ng , tas k d e l e g at i on, an d resu l t eva l uat i on, w hil e a n s -a g ent i s respons ibl e for tas k execut i on, co m pet i t i on, an d cooperat i on. In t h e ill ustrat i ve examp l e i n F ig . 8.7, suppose a use r w r i t es a f ew wo r ds o n his o r her PDA re g ardin g what he o r s he plans to do. A c-a g e n t in the distributed UAC will reco g nize the user’s intention an d fin d s imilar se r v i ce c a ses fr o m it s c a se b a se. T hereafter, it will execute task plannin g based on the similarit y between the tasks at h an d an d t h e prev i ous tas k s. Once t h e c-agent comp l etes t hi s process, a c l uste r of s-agents w ill b e ca ll e d upon to di str ib u t e an d carry out t h e p l anne d su b tas k s. E ac h s-a g ent w ill h ave di st i nct ro l e ( s ) an d will coo r di nat e i t s a c t i o n s wi t h t hose of ot h er s-a g ents i n a UAC. For i nstance, a ma il a g ent w ill b e respons ibl e for mana g - i n g ema il s, i nvo l v i n g t h ree di st i nct ro l es: e di t i n g , sen di n g , an d rece i v i n g . As t h e mail a g ent works, it will als o tak e int o co n s i de rati o n th e wo rk s tat us o f r e lat ed s -a g ents. In other words, i t w ill decide, after communicatin g with other s-a g ents, w h e n t o r ece i ve o r se n d e mail s an d w hat co nt e nt t o in c l ude. B ecause many ubiquitous agents have been devised for different services and f unctions in the U-society, a solution for clustering them is necessary in order to s ummon these heterogeneous agents roaming across the entire U-society and qu i c kly a gg re g ate t h em i n t o a seam l ess commun i t y , s u ch as t h e UAC , w hi c h w ill comp l ete user-spec i f i e d tas k s. 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Rational competition and cooperation in d ubiquitous agen t communities. Knowledge-Based System, 2004, 1 7: 189 – 200 . K.S. Teng, M. Maheswaran. Limited scope probing: A distributed approach f or QoS-based routing. In IEEE International Symposium on Networ k Comput i n g an d App li cat i ons ( NCA’01 ) , Cam b r idg e: Massac h usetts, 2001, 3 5 0 – 3 5 4. 9 Multiagent Communication for e-Business using Tuple Spaces H.F. L i , T. Ra dh a k r i s h nan, an d Y. Z h ang Department of Computer Sc i ence an d Software Eng i neer i ng Concordia Universit y , Montreal, Canada H3G 1M8 9.1 Introduction 9 .1.1 Motivation Th e g rowt h i n We b - b ase d app li cat i ons, di s tr ib ute d comput i n g , an d a g ent- b ase d software technologies has created abunda nt interest in various aspects of a a e -business. One such application supported b y these technolo g ies is e-commerce i n w hi c h o nlin e tran s a c ti o n s between a bu y er and a seller are su pp orted in various s ta g es of their tradin g (Gutman et al., 1998). E-commerce application s y stems have to deal with a large number of int e racting autonomous tasks using heteroge- neous information sources. These interacti o ns have a need to be well coordinate d and coordination re q uires efficient commun i cation among the entities. The dynamic an d comp l ex nature of e-commerce requ i res a f l ex ibl e tec h no l og i ca l i nfrastructure to support b us i ness processes more eas il y an d effect i ve l y. A g ent-based software technolo gy has become the sub j ect of much research in a wide ran g e of fields, especiall y in d i stributed s y stem desi gn . Multia g ent s y stems are often used in a d y namic environment with autonomous problem solvin g enti - ties cooperating and coordinating with each other. A typical software agent has the characteristics of autonomy, reactivity, proactivity and sociality, or structured i nteractions with other software agents. This makes the multiagent systems a natu- ra l can did ate c h o i ce for i mp l ement i ng e-commerce app li cat i ons. Bus i ness processes i n e-commerce may b e cons i d ere d as a ki n d of coor di nate d mu l t i agent system i n w hi c h t h e software agents perform var i ous mar k et act i v i t i es un d er dy nam i c partners hi ps. W i t h t h e i ncreas i n g comp l ex i t y of t h ese app li cat i ons, we nee d pro g ramm i n g mo d e l s to d ea l w i t h t h e coor di nat i on of a l ar g e num b er o f concurrent ly act i ve ent i t i es. T h us, an i nfrastructure fo r coo r di nat io n is n eeded t o meet the complex and dynamic requirements. Tu p le s p ace that s u pp orts inter - agents coordination is a n attractive solution. F or this purpose, our research focuses on tuple space-based agent coordina - t i on an d tup l e space- b ase d agent programm i ng framewor k ( TSAF ) t h at effec- t i ve l y supports b u ildi ng agent app li cat i ons i n e-commerce. In t h e rest of t hi s c h apter, we di scuss mu l t i agent i nteract i ons t h roug h tup l e space, present i ng h ow tup l e space fac ili tates t h e dy nam i c coup li n g s amon g a g ents. We a l so present an [...]... matching tuple to the access This provides flexibility in using multiple tuple spaces for separate purposes (such as 9 Multiagent Communication for e-Business Using Tuple Spaces 203 different markets), rather than a single tuple space with a possible degradation in performance Reactivity of a tuple space is considered in MARS [6] by introducing the notion of reactive tuples An agent can program the tuple... tuples via a logic-template to improve the flexibility of agent collaboration protocols Figure 9 .6 outlines the set of primitives that we have implemented in Java In the following, selective explanation is offered for some of the primitives shown in Fig 9 .6 Fig 9 .6 Interaction primitives 210 1 2 3 4 5 6 7 8 9 H.F Li et al TSCreate(String name) This primitive enables an agent initially to create a tuple... to one, or many to many The arrows show the initialization direction of interactions 9 Multiagent Communication for e-Business Using Tuple Spaces 219 Market Customer Product information acquisition Initializing searching Trading History Recorder r Information Searcher Register Products information acquiring g Customer Manager Mall Manager Register Initializing buying Initializing buying Fixed price... Multiagent Communication for e-Business Using Tuple Spaces 225 Performance Aspects The implemented e-market was exercised with sample test data to study its perm formance aspects On the one hand, we have claimed that the tuple space approach to system development is simpler than that based on agent-to-agent message communication On the other hand, we needed to know how much the performance would suffer... business logic We further extended JADE [8, 12] to reactive tuple space for the t support of agent interactions Figure 9.4 shows the overall architecture of the JADE platform Fig 9.4 JADE architecture The JADE platform is composed of several containers Every container runs on a Java virtual machine and can host zero or more agents The platform can be actually distributed across several hosts, and an agent... supplies stable interfaces for agents In addition, there is a connector in the shell The connector performs the exchange and transformation of data between an application agent and the kernel level The kernel processes tuple accesses from the shell locally or remotely, and returns appropriate responses If the required tuple space is located in a remote container, the kernel forwards the request to the... synchronization is required among cooperating agents Since these are the common forms of relationship between functions performed by agents, tuple space is a natural medium for coordinating multiagent activities Extensions of Tuple Primitives and Reactive Tuples In addition to the basic primitives, several extensions have been reported [6 8] Collectively, these extensions provide additional flexibilities in... goal-directed behaviors to perform some intended tasks Collaborations with other agents to perform such tasks are often needed An agent may have to play multiple roles As a result, each role-based behavior can be defined to perform a specific task The “main role behavior” is a proactive behavior that runs periodically as a dispatcher of other role-based behaviors In the e-market application, for example, a seller... buyers Thus, a buyer agent may have three role-based behaviors: searching for information, bidding for products, and negotiating with seller agents In contrast to the traditional agent architectures, our TSAF has the following three benefits labeled a, b, and c: (a) Separate Sensory Part from the Coupling Part There are two ways for an agent to learn about its outside environment One is to sense the... them separately The sensory part performs the works of periodically perceivt ing the environment for some specific parameters and keeping them in the internal shared database for successive stages of decision-making or reactions On the other hand, an agent still faces one or more tasks to be solved through collaborating with other agents The coupling part just performs this work to provide unified interfaces . and perform - ance of a mobile agent system. Software Practice and Experience, 2002, 3 2 ( 6 ) : 543–573. 8 . H. Pe i ne, T. Sto l pmann. T h e arc hi tecture of t h e Ara p l atform for mo bil e agents Fi g ure 9 .6 outlines the set of p rimitives that we have i m p lemented in Java. In the followin g , selective explanation is offered for some of the p rimitives shown in Fig. 9 .6. F ig. 9 .6. Interaction. i nformat i on suc h as w h o wrote i t an d w h o sent i t ( e i t h er or i g i na ll y or from t h e i nterme di ate l ocat i ons ) . T h e in format i on can b e furt h er use d for