Towards Efficient Selection of Web Services

Transcription

1 Towards Efficiet Selectio of Web Services Amir Padovitz School of Computer Sciece & Software Egieerig, Moash Uiversity Shoali Krishaswamy School of Computer Sciece & Software Egieerig, Moash Uiversity mailcssemoasheduau Seg Wai Loke School of Computer Sciece & Software Egieerig, Moash Uiversity ABSTRACT I the existig frameworks for web services there is o icetive to bid dyamically to a specific web service However, oce rutime iformatio cocerig those web services is available to the applicatio, dyamic bidig becomes advatageous over a static pre-decided oe We propose a model that provides web service cliets with rutime iformatio that is pertiet to its executio ad busiess logic Whe faced with multiple service providers who ca provide the same (i fuctioality) service, the cliet ca dyamically select the curret best (eg, i terms of availability for the duratio of the service, reliability, ad estimated respose time) service provider for its required service, accordig to the cliet s costraits ad iformatio gathered about the service providers at rutime INTRODUCTION Web Services are software applicatios or services that are uiquely idetified by a URI (Uiform Resource Idetifiers) ad expose public iterfaces for cliets, usig XML (exteded markup laguage) Those web services ca be discovered ad used by other cliet applicatios usig XML based messages ad protocols such as HTTP The emergece ad cotiued developmet of web services stadards such as SOAP (simple object access protocol) ad WSDL (web services descriptio laguage) [4] eable us to request ad describe web services i a stadard way This will icrease the ease of use of web services, eable iteroperability betwee heterogeeous platforms ad help busiesses solve itegratio problems of their applicatios Cosequetly, it is aticipated that web servers that host the services will be subject to icreasig usage ad have a higher load Furthermore, the curret simple modus operadi ivolvig cliet/server activatio of a sigle web service will be ehaced to support more complex scearios, i which applicatios ad service providers themselves rely o other exteral web services as part of their busiess logic The reliace o third party web services reduces the cotrol of the orgaizatio over its applicatio ad (sometimes) missio-critical code The cotrol ad iformatio of certai parts of the system is pushed outside orgaizatioal boudaries Scearios ivolvig reliace o exteral web services raise several ew issues ad challeges A example of commo sceario would be of cliets cosumig exteral web services, which i tur outsource their computatioal resources to other service providers Furthermore, rutime iformatio such as service load ad availability or busiess related costraits might affect the selectio process of a exteral web service, ad ot be predecided, as it is today I the existig frameworks for web services there is o icetive to bid dyamically to a specific web service However, oce rutime iformatio cocerig those web services is available to the applicatio, a dyamic bidig becomes advatageous over a static, pre-decided oe We suggest a model that provides the web service cliet rutime iformatio that is pertiet to its executio ad busiess logic The cliet applicatio ca the dyamically bid to the temporarily best service, from a selectio of acceptable web services it works with, ad accordig to the cliet s set of costraits A cliet may wat to apply some busiess rules whe dyamically choosig a web service, or may be more cocered with respose time or availability Whe respose time is critical (eg stock quotes service etc) it is importat for a applicatio to activate the fastest web service available at that give time, or have some mechaism that esures availability ad reliability Whe several cliets participate i such a sceario, a idirect load balacig mechaism is created, which helps to direct cliets to available ad relatively fast web services Figures ad 2 illustrate a cliet activatio decisios based o iformatio gathered at rutime from the service providers accordig to the cliet costraits I figure, the cliet is cocered with availability ad respose times of a web service; after retrievig related iformatio from the service providers, it activates the fastest available web service This behaviour cotributes to the robustess of the cliet applicatio Figure 2 shows cliet activatio, based o respose time ad quality of service Accordig to the cliet s busiess costraits, it may prefer to switch to aother service provider whe it observe a chage i the combiatio of quality ad respose time offered by the service providers Cliet activatio SP SP2 SP3 SP4 total respose time = 8 sec uavailable total respose time = 5 sec total respose time = 5 sec Figure web service activatio accordig to respose time ad availability

2 SP - high quality total respose time = 4 sec SP - high quality total respose time = 8 sec Cliet activatio SP2 - low quality total respose time = 5 sec Cliet activatio SP2 - low quality total respose time = 5 sec Figure 2 - dyamic activatio accordig to respose time ad quality of service I order to facilitate dyamic selectio, up to date iformatio cocerig parameters that affect the decisio of web service activatio must be gathered We are curretly developig ad ivestigatig a system that retrieves rutime related iformatio from service providers accordig to the cliet costraits ad specificatios ad decides which web service to activate To eable such fuctioality we examie two paradigms the traditioal RPC (remote procedure call) approach ad a mobile aget approach We draw three differet coceptual models based o these techologies ad compare their stregths ad weakesses While the first two are based o applyig the wellkow RPC ad Mobile Aget paradigms, we also itroduce a ovel Circulatig Mobile Aget model that exhibits differet characteristics ad complemets the first two The paper is orgaized as follows I sectio 2 we itroduce related work Sectio 3 presets architectural models for the dyamic selectio of web services Sectio 4 draws a quatitative aalysis for the use of those models Sectio 5 discusses implemetatio details of the prototype that supports the models described i sectio 3 We coclude ad discuss future work i sectio 6 2 RELATED WORK Mobile software agets are uits of code capable of migratig to differet hosts while maitaiig their ad state of executio Mobile agets display autoomous behavior, which implies a capability to hadle various scearios idepedetly, without a eed for some applicatio maagemet layer Cosequetly, they are capable of performig asychroous tasks ad reduce commuicatio overheads Aother importat feature mobile agets possess is the ability to work i heterogeeous eviromets Curretly, Agets reside i dedicated server applicatios, which ca potetially be activated o ay platform Furthermore, they preset fault tolerace ad robustess characteristics, as failure of a specific ode i a etwork will affect oly agets physically located o that ode at that time These characteristics ca become very useful whe itegrated i large ad heterogeeous etworks such as the Iteret ad provide a alterative to the RPC approach, icludig web services Web services may evolve to become more aget like ad ejoy the agets autoomy, iteractio capabilities ad add robustess ad efficiecy effects o the system [5] The mobile aget paradigm ca also coexist with web services ad both ca mutually beefit from each other stregths I this work we preset a attempt to itegrate the two approaches i oe system to extract the beeficial characteristics of both A importat step towards the itegratio of mobile agets ad web services is the work beig doe o the creatio of the sematic web ad the developmet of ew web markup laguages such as DAML (DARPA Aget Markup Laguage) [6] ad OWL [7] as well as otology of services such as DAML-S that aims to eable the discovery, activatio, moitorig ad selectio of web service by agets [8] A similar cliet orieted approach is take by [] to perform load balacig of Iteret services by movig parts of the load balacig decisio makig from the server to the cliets Other systems [2] also use cliet-orieted approaches to ehace the overall file system performace 3 ARCHITECTURAL MODELS I this sectio, we preset architectural models that assist i dyamic activatio of web services We preset three models: a RPC based approach, a mobile agets approach ad circulatig mobile agets I order to illustrate the models ad their respective modes of operatio we use the followig sceario show i figure 3 As see, each participat ca be both a cliet ad source of iformatio, eg a service provider ca be the source of iformatio for aother cliet as well as a cliet requestig iformatio o other web services cliet A A2 A3 Figure 3 - depedecies betwee service providers I this sceario a cliet wishes to retrieve iformatio o a service of type A Three service providers are available: A, A2 ad A3 Those service providers are themselves depedet o other web B B2 B3 C C2 C3 C4 D

3 services to complete their tasks For example service A is depedet o service B, which is depedet o service C, etc (A B C D) Here, the service providers, i tur, gather iformatio about other service providers they deped o This depedecy makes it more difficult for a service provider to accurately estimate iformatio such as the total time for processig a cliet request Whe attemptig to retrieve iformatio o a web service several cliet costraits should be imposed o the system For example, the cliet should have the ability to limit the duratio of the iformatio retrieval process or the depth (or level) of the etwork the iformatio is to be retrieved from Figure 4 illustrates a possible outcome of this approach whe activated o figure etwork, with a cliet that restricts the depth to 3 service provider levels ad has a timeout costrait for the search: A B C tree depth costrait D 3 RPC based model I traditioal wide etwork scearios (eg iteret) the most straightforward approach for gatherig iformatio for web services activatio would be to use RPC (remote procedure calls) for commuicatig iformatio betwee hosts i the etwork For platform idepedece, web services themselves ca be the meas by which commuicatio betwee two hosts is performed Iformatio could the be easily ad geerically set ad received betwee all the participats i the etwork This kid of implemetatio is geerally beeficial i wired etworks, as multiple coectios eed to be hadled, which may become problematic i wireless eviromets where coectios are less reliable I this model a compoet-orieted approach is take, i which a cliet/service provider is treated as a black box Whe a service provider receives a request, it may become a cliet ad actively request iformatio from other service providers This approach simplifies the programmig complexity of a eviromet cosistig of may service providers This model also supports complex scearios where service providers support several web services ad a cliet requires iformatio o more tha oe service This is show i Figure 5 cliet A2 C2 S4,S5 SP B2 A3 B3 timout Figure 4 - possible results of ifo retrieval timout C3 C4 cliet S2,S3 S,S2 S3,S4 S,S2, S5 SP5 SP2 SP3 SP4 I the example above, oly the route: cliet A3 B2 C2 yields a result, which is commuicated back to the cliet by service provider A3 Other service providers are uable to formulate the desired iformatio for the cliet Factors that limited the iformatio gatherig routes i this sceario are: a tree-depth costrait betwee odes C ad D (which has reached the fourth level), ad a timeout costrait betwee B2 ad C3 ad B3 ad C4 (i this case we assume a relatively log processig time by service provider C3 ad C4) We have show a possible sceario that depicts a etwork i which iformatio is gathered for a web service; we ow preset three models that support this iformatio gatherig for selectio before activatio behaviour 3 Models for Dyamic Selectio of Web Services We propose three differet models for dyamic selectio Each of these models has its ow stregths ad weakesses ad is best suited for particular situatios We aim to itegrate all three approaches ad create a hybrid model to cater for differet situatios Figure 5 S, S2, S3, S4, S5 - Web Service Types SP, SP2, SP3, SP4, SP5 - Service Providers The cliet seds requests to all the service providers; each request cotais iformatio o all the desired services from the recipiet The that is retrieved is the examied ad raked by the cliet s system Followig this rule the amout of requests per service desired is miimized (istead of iquirig all service providers several times, each is iquired oly oce) I this architecture, decisios regardig the ways to query ier depth odes i the etwork or decisio o which odes to query ad whe, are all delegated to the service provider, which the becomes itself a cliet of the system I this compoet-orieted scheme, the iitial cliet delegates future decisios ad implemetatio details to sub-cotractors, i the form of the service providers Oce a request is lauched, parameters cotaied i the request caot be chaged, eve if sometime alog the way the criteria for performig future requests have chaged The iitial cliet o loger has the cotrol over the operatio

4 Aother problem is the high amout of messages set betwee cliet ad service providers This limits the reliability of such a system i a wireless eviromet, where coectios are less reliable Furthermore, the higher the umber of participats, the more messagig is ivolved, resultig i more traffic cogestio 32 Mobile Agets based model To address the issue of wireless coectivity ad cliet cotrol we propose a secod model, based o mobile agets We examie two approaches that differ i the type of behaviour agets perform I the first model, agets are lauched by the cliet, arrive at the service providers, query iformatio, ad if eeded, cotiue to look for depedat services required iformatio Agets cotai cliet restrictios such as timeouts ad maximum umber of hops as well as other that pertai oly to the specific cliet Followig this approach, two agets of differet cliets may act differetly uder similar circumstaces give differet cliet directios for behaviour Figure 6 shows a possible strategy performed by agets a ad b that are lauched by the cliet Upo arrivig at service of type A they are redirected to retrieve iformatio from service providers B ad B2 The they are redirected agai to gather iformatio pertaiig to services C, C2 ad C3 After arrivig at B2 aget b cloes itself ito 2 agets, each travelig o a differet path to accomplish its task cliet a A B b C C2 The mai disadvatage of this approach however is that it is less realistic i a busiess sese It is ulikely that a cliet aget would be permitted to be redirected ad iteract with odes that the service provider is cocered with Service providers may have for example private agreemets with other service providers ad would ot wat to sed a aget that represets the iitial cliet It may also be agaist the best iterest of the cliet, sice sometimes a direct request for a service would result i a higher price tha if the other service provider hadled it The secod approach assumes iteractio of the cliet aget oly with the required first level service providers This approach is similar to the RPC oe, where service providers are treated as black boxes Although we loose the cliet cotrol characteristics, we still maitai better performace i wireless eviromets, compared with the RPC model Figure 7 shows this approach; agets operate o behalf of their cliets ad are restricted to iteract oly with the required first level service providers cliet cliet A A2 A A2 B B2 B3 B3 B C B2 C2 C3 b B2 A2 b2 Figure 6 first mobile agets approach C3 Figure 7 - secod mobile agets approach Figure 8 depicts the differeces betwee the RPC ad Mobile Agets models i terms of the umber of wireless coectios I the RPC model the cliet maages 5 coectios to all 5 serviceproviders, while i the Mobile Agets model oly coectio is established ad used to sed a sigle mobile aget that cloes itself ad arrives to all the service providers autoomously I this approach we gai a cliet cotrol of the aget behaviour also i deeper ode levels, after the iitial ecouter with the first service provider O top of cliet cotrol, we also gai better reliability i wireless eviromets, as the amout of coectios is highly reduced compared with the RPC model I this model the cliet (a wieless device) oly maitais coectios as per the amout of agets it iitially lauches A mobile aget should also be embedded with the ability to chage its migratio path if ecoutered with discoected or uresposive odes Despite their higher level of abstractio, implemetig agets to work i a large etwork of depedable service providers may be more complex Istead of treatig the service providers as black boxes as i the first model, the agets eed to be programmed to move aroud the etwork autoomously ad respod to possible chages i the eviromet 33 Circulatig Mobile Agets model The two previous models are suitable to work with web services that are expesive to purchase ad/or cosume a overall log processig time Sice the task of collectig iformatio is time cosumig, it is less likely these approaches will be utilized whe it is imperative to perform fast activatio of short-term ad iexpesive web services For such scearios, a third model is proposed that ca provide service providers related iformatio o demad The idea behid this model is havig mobile agets periodically circulatig the path of the service providers ad retrievig iformatio The iformatio is the give to the cliet, which the performs web service activatio I this sceario, iformatio that arrives is more updated ad is available sooer

5 RPC Mobile Agets ' a ' cliet Wireless '' cliet Wireless a '' ''' a2 ''' '''' '''' Figure 8 - differeces i umber of wireless coectios betwee the models cliet a c Figure 9 circulatig mobile agets Alog with its beeficial characteristics, this model may also suffer from a varied amout of redudacy Depedig o the cliet applicatio, agets may circulate the etwork, retrievig iformatio without ay curret eed to do so To miimize this redudacy, a ability to cotrol the amout of circulatig agets ad the duratio of their life cycle will be itroduced Table activatio cosideratios of the differet models Service Characteristics RPC MA Circulatig MA Expesive, log processig time X X Fast respose is importat X Network Characteristics Wired X Wireless X X ''' ' b '' 4 QUANTITATIVE ANALYSIS FOR USAGE OF THE MODEL Havig preseted the three models, we ow aalyse the suitability of the models with respect to the respose time criterio However, we ote that cliets may have additioal criteria for activatio such as price I this paper, we focus o respose time ad draw a quatitative represetatio of the processig time of the differet models We also preset rules goverig the system activatio decisio based o respose time for each mode of operatio We defie Treqi as the time it takes for a request to be set to a specific service provider i, Tresi as the time it takes for a respose to be set back from a specific service provider i, Twsi as the average time it takes for a web service to complete for a specific service provider i ad Tas i is the total time it takes for a service provider i to produce iformatio about the user requested parameters We defie T*req, T*res ad T*ws as the request, respose ad processig times of the web service that is selected by the system service cliet provider Selectio Activatio Treq Figure 0 Basic termiology { Tres{ T*req { T*res{ }Tas } T*ws

6 4 RPC Model O average, the total time for activatig a web service without usig the RPC model would be: Tavg = ( Treqi + Tresi + Twsi ) ad the total average commuicatio time would be ( Treqi + Tresi ) where is the umber of service providers offerig similar web services for the cliet to choose from Let Ta = Treqi + Tresi + Tasi Ta therefore represets the total time for a cliet to query service provider i for iformatio The total activatio time of the selected web service is represeted by Tactivatio, ad is: Tactivatio = T*req + T*res + T*ws We express the duratio of the processig time of a sequetially activated RPC model as follows: Trpc = ( Treqi + Tresi + Tasi) If the RPC messagig is performed i parallel, we ca express it as follows: Trpc = Treq+Tres+Tas Trpc2 = Treq2+Tres2+Tas2 Trpc3 = Treq3+Tres3+Tas3 Trpc = Treq+Tres+Tas Equatio Trpc = max (Trpc, Trpc2, Trpc3 Trpc) Ad the total activatio time of the RPC model is therefore: Trpc_total_activatio = Trpc + Tactivatio We ca formulate a geeral rule for activatig the RPC model with respect to respose time, ad state that wheever Equatio is observed, the cliet is ecouraged to use the RPC model, as it gais a better overall respose time compared with a average usage of a radomly selected web service Equatio 2 Trpc_total_activatio < Tavg Equatio 2 is more likely to occur if high variatio i the activatio time of web services (Twsi) is observed I such a case, it is more likely that Trpc_total_activatio will be less tha Tavg Furthermore, we argue that sice the cliet may ot be cocered oly with respose time, it is likely that it would prefer to use the RPC model eve if it has a loger total respose time, to a certai extet We deote this argumet i Equatio 3, where a cliet still prefers to use the model as log as it is ot loger tha a specific time amout Equatio 3 Trpc_total_activatio < Tavg + δ Where δ deotes a extra amout of time A example of this would be whe a cliet is more iterested i guarateeig the reliability of the service or is cocered with the service pricig, rather tha just the respose time I such cases it will be willig to pay for a loger process 42 Mobile Aget Model We defie Tmi,j as the migratio time betwee ode i ad ode j i a etwork represets the total umber of participatig odes (ie the service provider odes ad the cliet We cout the cliet as the first ode) We ivestigate a model i which the agets oly visit service providers i the first level of the service providers etwork Whe oly a sigle aget is lauched, the total migratio ad query time of the mobile aget model is: Equatio 4 Tma = Tm, + ( Tmi, i + ) + Tasi i = 2 Ad the total activatio time of the Mobile Aget model is: Tma_total_activatio = Tma +Tactivatio The rule for activatio of the mobile aget model follows the same guidelies as the RPC model: Equatio 5 Tma_total_activatio < Tavg + δ A geeral form for multiple agets lauched ca be described as follows: M, M2, M3 MN deote the total idividual migratio ad query times for N agets a deotes the umber of agets participatig M = T / a ( / a) *, ( + ) + T( + ), + ( Ti, i + ) + Tasi i = i = 2 ( / a)*2 M2 = T ( / a)*2,( + ) + T( + ), + ( Ti, i + ) + Tasi ( / a) + i = 2 M3 = T ( / a)* ( / a)*3,( ) T( ), ( Ti, i + ) + Tasi i = ( / a)*2 + i = 2 MN = T ( ),( + ) + T( + ), + ( Ti, i + ) + Tasi ( / a)*( a ) + i = 2 The maximal migratio ad query time for the Mobile Aget model that uses multiple amouts of agets would the be: For simplicity we assume that service providers are equally divided betwee agets

7 Equatio 6 Tma = Max (M, M2, M3 MN) I this case we measure the migratio ad query time of the slowest aget betwee differet platforms May applicatios today utilize the Net platform for their web services ad applicatios, while mobile agets are usually java based I such eviromets a utility i the form of VMSBridge is eeded to trasfer iformatio betwee the two virtual machies 43 Circulatig Mobile Agets model Based o Equatio 4, which depicts the total migratio ad query time of a sigle mobile aget i a etwork, we ca preset the average time for a system to be otified by oe of its N circulatig agets, as follows: Cliets WSAdvisor WSRepository Equatio 7 Tcirculatig = Tm, + ( Tmi, i + ) + 2 2N Tasi Where we assume a uiform distributio of circulatig agets ad similar processig times of service providers for cliet s iformatio queries The omiator i Equatio 7 presets the total time it takes for a circulatig aget to start circulatig aget ad to arrive back to the system ad iforms o the iformatio collected This is divided by N Circulatig Agets to deote the maximal time it takes sigle aget to arrive back Fially, this is further divided by 2 to deote the average time for a aget to arrive back I other words, every aget arrives back i Tma / N, ad o average i (Tma / N) / 2 This ca be aalyzed also from a cliet poit of view I the circulatig model, a cliet that wishes to employ the circulatig agets, first eeds to iitiate the begiig of their circulatio i the etwork ad oly the after a certai amout of time request for iformatio I such sceario, (Tma / N) presets a top boudary for the time a cliet receives the iformatio Assumig that a cliet request for iformatio is uiformly distributed, a average time for a cliet to receive the system iformatio would be (Tma / N) / 2 The total activatio time of the circulatig model from a cliet poit of view would be: Tcirculatig_total_activatio = Tcirculatig + Tactivatio The activatio rule to be cosidered for circulatig agets would the be: Tcirculatig_total_activatio < Tavg + δ 5 Implemetatio of Prototype The architectural overview of the system is depicted i figure The mai fuctioality is implemeted i the WSAdvisor compoets; cliet applicatios iteract with this fuctioality either directly - whe requestig web service activatio recommedatios, or idirectly whe updatig iformatio o ew possible web services i the repository WSAdvisor compoets query that repository to obtai iformatio o web services ad create itierary for commuicatig with the service providers A aget server is used to lauch ew agets with itieraries to service providers destiatios A commuicatio utility object VMSBridge is used to facilitate decoupled commuicatio betwee the mai WSAdvisor compoets ad other third party applicatios VMSBridge also serve as a lik VMSBridge Figure high-level overview Aget server To facilitate a itegratio of the three models ad develop a system, which is scalable, geeric ad flexible, we have pursued a iitial desig that is depicted i figure 2 The followig sectio describes the fuctioality of the major classes i the desig AdvisorImpl, Advisor - The Advisor set of classes is implemeted as a proxy to be used by the cliet to iitiate requests for iformatio gatherig o particular web services Several modes of operatios are available for the cliet, icludig sychroous, asychroous ad optimised (cached) The default ad recommeded mode is optimised ad Asychroous operatio, i which the cliet is advised o recommeded web services Asychroously The user also specifies the rakig criteria for the service providers iformatio The implemetatio supports differet umbers of cliet applicatios Chai ad Operatios - The chai class maages the flow of operatios i a geeric way Operatios that adhere to the iterface IOperatio ca be added durig desig time or dyamically ad are cotrolled by the chai class We idetified four types of operatios, which are represeted by the Operatio classes: Iformatio, Cache, Itierary ad Activator These four basic operatios idetify the basic steps i the process of preparig the system to query iformatio from the service providers VMSBridge - VMSBridge offers a geeric ad decoupled way to bridge betwee differet eviromets such as Java ad Net virtual machies The idea behid this fuctioality is to eable maximum flexibility of the framework to work with differet third party applicatios For example Net based cliet applicatios ad Java baesd aget toolkits WSMaager, AgetMaager - The maager classes cotrol the activity of commuicatig with the service providers This activity is pursued either with a RPC or mobile agets approach Rakig - Upo receivig iformatio collected from the service providers, it is set to be raked accordig to the user request The rakig follows a multi-dimesioal shortest distace approach, as described i [3] Weights are calculated i referece to the user specificatios

8 DAO - A layer that commuicates with a repository of web services descriptios that are dyamically added ad cotrolled by the cliet <<iterface>> IAdvisor Rakig AdvisorImpl <<proxy>> Advisor Chai <<iterface>> IOperatio Cache Iformatio Itierary Activator DAO <<sigleto>> VMSBridge <<iterface>> IMessageHadler Aget Message <<iterface>> IVisitor AgetMaager <<iterface>> ICommad WSMaager Visitor ComplexVisitor Commad Figure 2 system class diagram 6 Coclusios ad Future Work We are curretly i the process of implemetig the WSAdvisor system, which selects related service provider iformatio for the activatig cliet We aim to aalyze results draw from the activatio of the RPC, Mobile Aget ad Circulatig models ad lear more about their performace characteristics i large-scale distributed eviromets such as the Iteret The ext implemetatio step ivolves the developmet of a hybrid model that itegrates the existig models ito oe 7 Refereces [] Yoshikawa C, Chu B, Eastham P, Vahdat A, Aderso T Culler D Usig Smart Cliets to Build Scalable Services Proceedigs of the {USENIX} 997 Aual Techical Coferece [2] Aderso T, Dahli M, Neefe J, Patterso D, Roselli D, Wag R Serverless Network File Systems Proceedigs of the 5 th ACM Symposium o Operatig Systems Priciples, pp December 995 [3] Krishaswamy, S, Pi, E, P, Ho, J, Guawa, W, A XML Specificatio Laguage to Support A Virtual Marketplace of Data Miig E-Services, 2002, Proceedigs of the Workshop o Data Sematics i Web Iformatio Systems (DASWIS 2002) held i cojuctio with Third IteratioaL Coferece o Web Iformatio Systems Egieerig (WISE 2002), Sigapore, December, pp , IEEE Press

9 [4] World Wide Web Cosortium (2000/200): Web Services, exteded Markup Laguage (XML), Simple Object Access Protocol (SOAP), Web Services Descriptio Laguage (WSDL) Available at: [5] Huhs M N Software Agets: The Future of Web Services Aget Techology Workshops 2002, LNAI 2592, pp -8, 2003 [6] Hedler J, McGuiess D L DARPA Aget Markup Laguage IEEE Itelliget Systems, 5(6):72 73, 200 [7] Dea M, Coolly D, va Harmele F, Hedler J, Horrocks I, McGuiess D L, Patel-Scheider P F ad Stei L A OWL Web Otology Laguage I Bradshaw J, editor, Software Agets MIT Press, Cambridge, 997 [8] DAML-S: Sematic Markup for Web Srevices Submitted for publicatio i The Emergig Sematic Web