第2期 LI Xining ,et al Dispatching mobile Agents for DDM applications ·183 sets distributed over the Internet.Deploying mo- states via broadcasting to anyone who is listening. bile agent paradigm in DDM offers a possible solu- A service advertisement should consist of the serv- tion because the application may decompose data ice identifier,plus a simple string describing what mining problems to scale up to a large distributed the service is,or a set of strings for specifications data sources and dispatch agents to carry out dis- and attributes. tributed data processing.This in turn leads us to The most significant feature of DSSEM is that the data service discovery problem,that is,how to we enrich the service description by using web find data sites available to a DDM application. page's URL to replace the traditional string-set Clearly,the number of services that will be- service description in mobile agent systems.That come available in the Internet is expected to grow is,service providers use web pages to advertise enormously.Examples are information access via their services.Because of the specific characteris- the Internet,multi-media on demand,Web serv-tics,such as containing rich media information ices and services that use computational infrastruc- (text,sound,image,etc.),working with the ture,such as P2P and Grid computing.In general, standard HTTP protocol and being able to refer- the service usage model is role-based.An entity ence each other,web pages may play a key role providing services that can be utilized by other re- acting as the template of the service description. questing entities acts as a provider.Conversely,an On the other hand,since the search engine is a ma- entity requesting the provision of a service is called ture technology and offers an automated indexing a requester.To be able to offer services,a provid-tool that can provide a highly efficient ranking er in turn can act as a requester making use of oth-mechanism for the collected information,it is use- er services.In a distributed system,requesters and ful for acting as the directory server in our model. providers usually live on physically separate hosts. Of course,DSSEM also benefits from previous Providers should from time to time advertise serv- service discovery research in selected areas but is ices by broadcasting to requesters or registering endowed with a new concept by combining some their services on third party servers. special features of mobile agents as well as integra- In the IMA GO system,we have implemented ting service discovery tool with agent servers. a new data service discovery model DSSEM (Dis- covery Service via Search Engine Model)for mo- nobile migrate gent search directory bile agents!.DSSEM is based on a search en search migrate engine gine,a global Web search tool with centralized in- dex and fuzzy retrieval.This model especially aims database nobile database gen access agent at solving the database service location problem database and is integrated with the IMA GO system.Data module advertise module service providers manually register their services in a service discovery server.A mobile agent locates a Fig I An example of service discovery and specific service by migrating to the service discov- data mining process ery server and subsequently submitting requests In principle,data service providers register with the required data description.The design goal the URLs of their websites that advertise all the of DSSEM is to provide a flexible and efficient information concerning services.As a middleware service discovery protocol in a mobile agent based on the service discovery server,the search engine DDM environment. will periodically retrieve web pages indicated in Before a service can be discovered,it should URLs and all their referencing documents,parse make itself public.This process is called service tags and words in documents and set up the rela- advertisement.The work can be done when serv- tionship between the keywords and the host ad- ices are initialized,or every time they change their dress of these service providers.On the other 1994-2009 China Academic Journal Electronic Publishing House.All rights reserved.http://www.cnki.netsets distributed over t he Internet. Deploying mo2 bile agent paradigm in DDM offers a possible solu2 tion because t he application may decompose data mining problems to scale up to a large distributed data sources and dispatch agents to carry out dis2 tributed data processing. This in t urn leads us to t he data service discovery problem , t hat is , how to find data sites available to a DDM application. Clearly , t he number of services t hat will be2 come available in t he Internet is expected to grow enormously. Examples are information access via t he Internet , multi2media on demand , Web serv2 ices and services t hat use comp utational infrastruc2 t ure , such as P2P and Grid comp uting. In general , t he service usage model is role2based. An entity providing services t hat can be utilized by ot her re2 questing entities acts as a provider. Conversely , an entity requesting the provision of a service is called a requester. To be able to offer services , a provid2 er in turn can act as a requester making use of oth2 er services. In a distributed system , requesters and providers usually live on p hysically separate hosts. Providers should from time to time advertise serv2 ices by broadcasting to requesters or registering t heir services on t hird party servers. In t he IMA GO system , we have implemented a new data service discovery model DSSEM (Dis2 covery Service via Search Engine Model) for mo2 bile agents [13 ] . DSSEM is based on a search en2 gine , a global Web search tool wit h centralized in2 dex and f uzzy retrieval. This model especially aims at solving t he database service location problem and is integrated wit h t he IMA GO system. Data service providers manually register t heir services in a service discovery server. A mobile agent locates a specific service by migrating to t he service discov2 ery server and subsequently submitting requests with the required data description. The design goal of DSSEM is to p rovide a flexible and efficient service discovery protocol in a mobile agent based DDM environment. Before a service can be discovered , it should make itself p ublic. This process is called service advertisement. The work can be done when serv2 ices are initialized , or every time t hey change t heir states via broadcasting to anyone who is listening. A service advertisement should consist of t he serv2 ice identifier , plus a simple string describing what t he service is , or a set of strings for specifications and attributes. The most significant feat ure of DSSEM is t hat we enrich t he service description by using web page’s U RL to replace t he traditional string2set service description in mobile agent systems. That is , service providers use web pages to advertise t heir services. Because of the specific characteris2 tics , such as containing rich media information (text , sound , image , etc. ) , working wit h t he standard H TTP p rotocol and being able to refer2 ence each ot her , web pages may play a key role acting as t he template of t he service description. On t he ot her hand , since t he search engine is a ma2 t ure technology and offers an automated indexing tool t hat can provide a highly efficient ranking mechanism for t he collected information , it is use2 f ul for acting as t he directory server in our model. Of course , DSSEM also benefits from previous service discovery research in selected areas but is endowed with a new concept by combining some special feat ures of mobile agents as well as integra2 ting service discovery tool with agent servers. Fig11 An example of service discovery and data mining process In principle , data service providers register t he U RLs of their websites t hat advertise all t he information concerning services. As a middleware on the service discovery server , t he search engine will periodically retrieve web pages indicated in URL s and all t heir referencing documents , parse tags and words in documents and set up the rela2 tionship between the keywords and t he host ad2 dress of t hese service providers. On t he ot her 第 2 期 L I Xi2ning ,et al :Dispatching mobile Agents for DDM applications ·183 ·