Document Sample

                                       Nadia Ben Seghir ,Okba Kazar
                              Department of computer science, University of Biskra
                                             07000, Biskra, Algeria

               Nowadays, the demand of information can be divided on several distributed
               systems, where it needs a reconstitution of response by a managing entity. Further,
               an exchanges data in a distributed application requires interaction between various
               entities through the network. The “client/server” model where exchanges are given
               by sending messages through the network is the most used model. This model has
               the disadvantage of increasing network traffic and it requires a permanent
               connection. In this article, we propose a new approach which uses the mobile
               agents’ technology. This last appears in this context as a promising solution
               facilitating the implementation of distributed applications. In this paper, we
               describe our architecture based mobile agents for searching information from
               distributed heterogeneous sources. Each mobile agent of research will be used to
               visit the site server of the application in order to collect information for its client,
               which allows him to interact locally with server, so it reduces the delay of the
               client waiting and the network traffic.

               Keywords: Mobile agent, Information retrieval, Distributed systems, Web.

1   INTRODUCTION                                              (research of the hotels, reservation of a plane ticket,
                                                              etc...), some agents move on different sites to search
     The evolution of the networks on a big scale             information for their clients. Many works have been
permitted the birth of a grand number of new                  elaborated in order to introduce the mobile agents’
applications that develops around this type of                technology in distributed information retrieval. The
network: electronic commerce, research of                     mobile agent concept appears in this context like a
information on the web, platform for distributed              solution facilitating the implementation of distributed
calculation, etc. These distributed applications need         applications.
to communicate and to exchange information                         We approached our architecture according to
between various entities.                                     these view-points. In this paper we propose an
     Today, the “client/server” model where                   approach based on mobile agents permitting to
exchanges are given by sending messages through               search for pertinent information from distributed
the network is the most used model. In this model,            heterogeneous sources.
only the client represents an application to the proper            The presented article is structured like follows:
sense of the term and the server’s role is to answer          in the next section we are briefly going to present a
the demands of the clients. The server constructs his         certain number of works that links mobile agents and
responses regardless of the client, so a part of the          the research of information, this part is consecrated
sent data is useless which increases the network              to the comparison of our approach with relatively
traffic. Besides, this model requires a permanent             near works. Thereafter, our new approach will be
connection between the client and the server, what is         detailed in the third section, first we present the
not the case of the mobile terminals that is exposed          general architecture followed by its components.
to the loss of the connection. In this article we             Finally, a conclusion shows the result of this research
propose a new approach which uses the mobile                  and presents the considered perspectives.
agents. These agents are the entities that move from
a machine to another on the network, without losing           2   RELATED WORKS
their codes or their states.
     One of the most important applications in the                 Since the first publications, the information
domain of mobile agents is the research of                    retrieval has been presented like a potential
information on the Web. In these applications                 important application of the mobile agents as the

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“killer application” [1]. Various significant works        model “mobile agent”, an agent is a process
have been led in the domain of the research of             possessing a context of execution, including the code
information and lean on the mobile agents’                 and data, capable to migrate during execution from
technology. Among these ones we distinguish:               machine to machine (called servers) in order to
     - In [4], the authors present an application of       realize its task that is assigned [7].
research of textual documents based on mobile                    Mobile agents have several advantages in
agents. It is about an application of simple research      distributed information retrieval applications. By
in a local network (with centralization of information     migrating to an information resource, an agent can
on the servers via a mechanism of yellow pages,            invoke resource operations locally, eliminating the
without constraint security, nor dynamic discovered        network transfer of intermediate data. By migrating
of new servers). The research agent leans on               to the other side of an unreliable network link, an
observation agents of the state in the network and on      agent can continue executing even if the network
a stationary agent that acts as interface with the local   link goes down, making mobile agents particularly
information server.                                        attractive in mobile computing environments. Most
     - The DBMS-Aglet system [10] implants a               importantly, an agent can choose different migration
solution based on mobile agents in Java for                strategies depending on its task and the current
interrogation of heterogeneous data bases via the          network conditions, and then change its strategies as
Web. A mobile agent transports the request on the          network conditions change. Complex, efficient and
site server where he dynamically acquires the pilot        robust behaviors can be realized with surprisingly
JDBC, then it puts its request and returns the results     little code.
on the client site.                                              In short, the true strength of mobile agents is not
     - M3 “Multimedia Database Mobile agents” [9]          that they make new distributed applications possible,
is a system of data multimedia research by the             but rather that they allow a wide range of distributed
content that rests on the mobile agents, Java and          applications to be implemented efficiently, robustly
CORBA. Mobile agent can memorize the                       and easily within a single, general framework.
information collected on a site, use them on the                 As already evoked, the proposed architecture in
visited sites, and make them evolve during the course.     this work is an approach based mobile agents
The problems of security are processed via                 conceived for searching information from distributed
mechanisms        of    independent     sessions,    the   heterogeneous sources. It defines a set of
mechanisms of security of CORBA, and via the               components (agents) and all functional modules
restrictions of rights.                                    described in term of their behaviors and interfaces, as
     - Finally other works as AGATHE [8],                  well as the way of interaction of these components in
ARCADIA [5], JAVANE [2], NETSA [6], and                    order to accomplish the set of tasks of the system
ISAME [11], propose another alternative for the            correctly.
research of information: models of mobile agents and
multi-agents.                                              3.2 General Architecture of the System
                                                                The general architecture of our system,
3   PRESENTATION OF THE PROPOSED                           illustrated in figure 1, articulates around four main
    ARCHITECTURE                                           layers in interaction.
                                                           3.2.1 Interface layer
     In this section, the objectives of proposed                This layer contains the application that allows
system are firstly presented, its general architecture     client to interrogate the system. Its essential role is to
putting in evidence its four main layers, its general      capture the user’s goal in order to respond his need.
functioning, and finally some details of                   It contains interface agents interacting with the user
implementation are provided.                               to help him to realize the precise task. This
                                                           interaction results in a transformation of the user’s
3.1 Objectives of the System                               demands that transformed in XQuery requests which
     To search, find and integrate information from        facilitate the function of mediator agent.
resources of data geographically dispersed is a            3.2.2 Mediation layer
difficult problem, which are confronted a numerous              This layer regroups all necessary elements to the
organizations. These last years, the size and the          execution of reformulating process of a query written
variety of accessible data by networks have                in global schema to a query written in sources
considerably increased. New solutions became               schemas. At the end of information research process,
necessary to manipulate information descended from         the mediator agent reassembles the information
dynamic resources as the World Wide Web. The               found as a global response that represents
mobile agent appears in this context as a promising        information demanded by the user.
solution, allowing the construction of flexible
applications, adaptable to the constraints of the
application and to the execution environment. In this

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Figure 1: Global architecture of the system

     Our mediator is achieved by integration process        - XQuery: as common language in which the
that can rest on GAV approach (Global As View) [3].       mediator will interrogate the resource agents.
With this approach the treatment of user queries is       XQuery is a rich query language that permits to
very easy. GAV consists on a mediated schema (the         interrogate some XML documents, its features allow
global schema) which is defined as a set of views         to categorize the main elements of language. It is
over the data sources. The definition of a mediator       descended of Quilt and takes the advantages of XQL,
schema on heterogeneous sources requires the use of:      and XPaths [12].
(i) common interrogation language; (ii) common            3.2.3 Research mobile agent layer
result format. To facilitate our mediator’s work, we           This layer contains set of research agents
chose to use:                                             generated by the mediator agent. In this level, and for
   - XML: as common result format in which the            each sub-query, the mediator agent activates one of
resource agents will respond the mediator agent. The      the created research agents. The researches agents
advantages of using XML as model of results               are the mobile agents browsing web to find
integration from the wealth of this language:             appropriate information to each received sub-query
abundance of the descriptions, data structure, clarity,   on different distributed data sources.
extensibility, etc...

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3.2.4 Information sources layer                                When the execution of the sub-queries is
     It is a class that is capable to receive some        finished, the mediator reassembles the results found
requests, treat them and return the results. This layer   by the group of research agents as a global response
regroups first a set of resource agents that is           that represents information demanded by the user
distributed on several sites to manage the set of         (see figure 3).
associated data to each site, and secondly the                 The mediator agent has the faculty to control the
multiple sources that provide the system basic data.      motivations of research mobile agents that arrive to it,
     Now, we are going to detail the different agents     which permits to increase the level of system
that include these layers.                                security.
                                                          3.3.3 Research mobile agent
3.3 Agents Specification                                       The research agents are the entities that can
    Our architecture includes four types of agents, as    migrate during execution from machine to machine
indicated in figure 1, in variable concentrations.        in network in order to satisfy the need of their clients.
3.3.1 Interface agent                                     On each machine, they do some exchanges and treat
    This agent can be seen like a simplifying that        the collected information.
allows the users to interact with the system (see              This treatment (filtering, sorting...) reduces the
figure 2). It is a stationary agent that is mainly        quantity of transported information with the agent
responsible to acquire all users’ requests, send these    and consequently the traffic on the network. The data
requests to the adequate agents and present the           demanded by mediator are transported by mobile
results to the users.                                     agent.

Figure 2: Interface agent structure                       Figure 4: Research mobile agent structure

3.3.2 Mediator agent                                           The figure 4 presents our typical architecture of
     The mediator agent is an intelligent agent that      research mobile agent. This architecture has a very
treats the distribution of data, it does a set of         simple nature because the power of system doesn’t
treatment on user query written in global schema in       lean on the complexity of an agent’s architecture, but
order to reformulate it in sub-queries written in the     on the interactions between the different agents and
sources schemas. It plays the role of interface           their roles.
between the user who puts a request and the set of
data sources. For each sub-query the mediator agent
will generate a research mobile agent to be displaced
toward the site server in order to find the adequate
information to the acquired sub-query.

Figure 3: Mediator agent structure

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3.3.4 Resource agent

Figure 5: Resource agent structure                           3.4.2 Implementation results
                                                                 We have created for each agent in the system a
     It is a stationary agent that acts locally during all   class inherits from “jade.gui.GuiAgent” class to give
its cycle of life in the machine where it has been           each agent a graphic window that permits to
implanted initially. This agent receives queries             visualize its interactions with other agents. The
formulated in XQuery, and transforms them in native          figures 6, 7, 8 present respectively the graphic
queries (proper for the source) in order to extract          representation of mediator agent, research mobile
required information from the local database (see            agent, and resource agent.
figure 5). The found information is translated then in
XML as a response to claimant’s query (research
mobile agent).
     Mainly, a resource agent manages only one data
source. Obviously, more the number of resource
agents is big, more we will have an access to a
complete and various information.

3.4 Implementation Details
     The scenario for which our approach has been
tested concerns the organization of voyage because it
is considered like a typical example for information
retrieval on the web. The scenario shows how our
system can help a user in his research about hotels
and restaurants in a city.
3.4.1 Hardware and software environment
     The agents of our system are implemented using
JAVA language, their development platform is
JADE 1 . JADE supports the development of agents
with the possibility to transport them from a system
to another. The Development multi-agents respects
the recommendations of FIPA 2 , notably that the
retained communication language is ACL-FIPA. All
programs are developed with JDK (Java
Development Kit) version 1.6. We develop the corps           Figure 6: Graphic representation of mediator agent
of classes in the programming environment
“JBuilder X”.
     The tests are achieved on an Ethernet network
that consists of 4 micro-computers Pentium 4, 3.2
GHzes, RAM 512 Mb, network LAN 100 Mbit/ses.

  Java Agent DEvelopment Framework :
  Foundation for Intelligent Physical Agents,

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Figure 7: Graphic representation of research mobile agents with its received sub-queries in XQuery

Figure 8: Graphic representation of resource agents with its found results in XML

     In order to understand clearly the function of our
architecture, we present in figure 9 the graphic
interface for agent “sniffer” of the platform JADE
that permits to visualize the exchange of messages
between different agents during treatment of user

Figure 9: Communication among agents of the system

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4   CONCLUSION                                            agents in order to achieve the demanded tasks
     In this paper, we were interested in mobile            - Extend the architecture for the use of Web
agents’ technology and its use for the information        Services (WS).
retrieval in distributed environments. The objective
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