A MULTI-AGENT SYSTEM FOR INFORMATION SHARING

Marco Mari, Agostino Poggi, Michele Tomaiuolo

DII, University of Parma, Parco Area delle Scienze 181/A, Parma, Italy

Keywords: Information sharing, multi-agent systems, peer-to-peer.

Abstract: This paper presents RAIS, a peer-to-peer multi-agent system supporting the sharing of information among a

community of users connected through the internet. RAIS has been designed and implemented on the top of

well known technologies and software tools for realizing multi-agent and peer-to-peer systems, for the

searching of information and for the authentication and authorization of users. RAIS offers a similar search

power of Web search engines, but avoids the burden of publishing the information on the Web and

guaranties a controlled and dynamic access to the information. Moreover, the use of agent technologies

simplifies the realization of three of the main features of the system: i) the filtering of the information

coming from different users on the basis of the previous experience of the local user, ii) the pushing of the

new information that can be of possible interest for a user, and iii) the delegation of access capabilities on

the basis of a network of reputation built by the agents of the system on the community of its users.

1 INTRODUCTION

The storage capability of hard disks is constantly

growing, while the new available space is quickly

filled with a large amount of data in different and

heterogeneous formats. The ordering of such data is

a time wasting and often boring task: the result is

that more and more files, containing important

information, are lost or forgotten on hard drives. The

classical file searching tools (e.g., Windows search

function) are not effective: for each request they

analyse the whole drive, and they support only few

file formats. In last months, the providers of the

main Web search engines (Google, Microsoft with

MSN and Yahoo!) have released desktop search

tools that make a research on a local drive as easy

and fast as a Web search. These tools run in the

background (when CPU load is low) and index the

content of a wide range of file formats (e.g.: Office,

PDF, e-mail, HTML, …) in a way similar to a Web

crawler. Moreover, Google has released an SDK for

its desktop search software. The SDK empowers

developers to write plug-ins thanks to a set of APIs

using COM and HTML/XML.

Besides a local drive, the better place to find files

and, more in general, information is the Internet. The

most used tools to share contents and information

avoiding the burden of exporting them on the Web

are peer-to-peer systems. The exchange of

multimedia files with a peer-to-peer system is highly

effective because their contents can be easily

categorized by the title. On the other hand, files

holding more information (e.g., documents, e-mails,

etc.) could be effectively shared only if the

categorization takes into account the whole content.

This paper presents a system, called RAIS, that

tries to couple the features of peer-to-peer

information sharing systems and the Web. The next

section introduces the main features and the

behaviour of the RAIS system. Section three

describes how this system has been designed and

implemented by using some well-known

technologies and software tools. Finally, section four

gives some concluding remarks and presents our

future research directions.

2 RAIS

RAIS (Remote Assistant for Information Sharing) is

a peer-to-peer and multi-agent system composed of

different agent platforms connected through the

internet. Each agent platform acts as a “peer” of the

system and is based on three agents: a personal

assistant, an information finder and a directory

facilitator; moreover, another agent, called personal

proxy assistant, allows a user to remotely access

147

Mari M., Poggi A. and Tomaiuolo M. (2006).

A MULTI-AGENT SYSTEM FOR INFORMATION SHARING.

In Proceedings of the Eighth International Conference on Enterprise Information Systems - SAIC, pages 147-152

DOI: 10.5220/0002446501470152

 SciTePress

her/his agent platform. Figure 1 shows the RAIS

multi-agent system architecture.

A personal assistant (PA) is an agent that allows

the interaction between the RAIS system and the

user. This agent receives the user’s queries, forwards

them to the available information finders and

presents the results to the user. Moreover, a PA

allows the user to subscribe her/him to be notified

about new documents and information on some

topics in which she/he is interested. Finally, a PA

maintains a profile of its user preferences: in fact,

the user can rate the quality of the information

coming from another user for each search keyword

(the utility of this profile will be clear after the

presentation of the system behaviour).

An information finder (IF) is an agent that

searches information on the repository contained

into the computer where it lives and provides this

information both to its user and to other users of the

RAIS system. An IF receives users’ queries, finds

appropriate results and filter them on the basis of its

user’s policies (e.g.: results from non-public folders

are not sent to other users). Moreover, an IF

monitors the changes in the local repository and

pushes the new information to a PA when such

information matches the interests subscribed by this

PA.

A personal proxy assistant (PPA) is an agent that

represents a point of access to the system for users

that are not working on their own personal

computer. A PPA is intended to run on a pluggable

device (e.g., a USB key) on which the PPA agent is

stored together with the RAIS binary and

configuration files. Therefore, when the user starts

the RAIS system from the pluggable device, her/his

PPA connects to the user’s PA and provides the user

with all the functionalities of her/his PA. For

security reasons, only a PA can create the

corresponding PPA and can generate the

authentication key that is shared with the PPA to

support their communication. Therefore, for a

successful connection, the PPA has to send the

authentication key, and then the user must provide

his username and password.

Finally, the Directory Facilitator is responsible to

DF is also responsible to inform the agents of its

platform about the address of the agents that live in

Internet

PPA

Figure 1: The RAIS multi-agent system architecture.

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the other platforms available on the RAIS network

(e.g., a PA can ask about the address of the active IF

agents).

2.1 Searching and Pushing

Information

In order to understand the system behaviour, we can

present two practical scenarios. In the first, a user

asks her/his PA to search for some information,

while in the second the user asks to subscribe her/his

interest about a topic. In both cases the system

provides the user with a set of related information.

In the first scenario, the system activity can be

divided in four steps:

: the user requests a search to her/his PA

indicating a set of keywords and the maximum

number of results. The PA asks the DF for the

addresses of available IF agents and sends the

keywords to such agents. The information finders

apply the search to their repositories only if the

querying user has the access to at least a part of the

information stored into its repositories.

Results filtering

: each IF filters the searching

results on the basis of the querying user access

permissions.

Results sending and presentation

: each IF sends

the filtered list of results to the querying PA. The PA

orders the various results as soon as it receives them,

omitting duplicate results and presents them to its

user.

Retrieval

: after the examination of the results list,

the user can ask her/his PA for retrieving the

information corresponding to an element of the list.

Therefore, the PA forwards the request to the

appropriate IF, waits for its answer and presents the

information to the user.

In the second scenario, the system activity can be

divided in five steps:

Subscription

: the user requests a subscription to

her/his PA indicating a set of keywords describing

the topic in which she/he is interested. The PA asks

the DF for the addresses of available IF agents and

sends the keywords to such agents. Each IF registers

the subscription if the querying user has the access

to at least a part of the information stored into its

repository.

Monitoring and result filtering

: each IF

periodically checks if there are some new

information satisfying its subscriptions. If it

happens, the IF filters its searching results on the

basis of the access permissions of the querying user.

Results sending and user notification

: each IF

sends the filtered list of results to the querying PA.

The PA orders the various results as soon as it

receives them, omitting duplicate results and stores

them in its memory. Moreover, it notifies its user

about the new available information sending her/him

an email.

Results presentation

: the first time the user logs

into the RAIS system, the PA presents her/him the

new results.

Retrieval

: in the same way of the previous search

scenario, the user can retrieve some of the

information indicated in the list of the results.

As introduced above, a PA receives from the

user a constraint on the number of results to provide

) and uses it to limit the results asked to each IF

agent. The number of results that each IF agent can

send is neither N

nor N

divided to the number of IF

agents (N

), but a number (between N

and

) for which the PA is quite sure to provide at

least N

results to its user without the risk of

receiving a burden of unnecessary data. Moreover,

each IF, before sending the list of results, creates a

digest of each result and sends them together with

the list. Therefore, the PA can use the digests to omit

duplicate results coming from different IF agents.

After the reception of results and the filtering of

duplications, the PA has the duty of selecting N

results to send to its user (if they are more than N

)

and order them. Of course, each IF orders the results

before sending them to the PA, but the PA has not

the information on how to order results from

different IF agents. Therefore, the PA uses two more

simpler solution on the basis of its user request: i)

the results are fairly divided among the different

sources of information, ii) the results are divided

among the different sources of information on the

basis of the user preferences. User preferences are

represented by triples of the form <source, keyword,

rate> where: source indicates an IF, keyword a term

used for searching information, and rate a number

representing the quality of information (related to

the keyword) coming from that IF. Each time a user

gets a result, she/he can give a rate to the quality of

the result and, as consequence, the PA can update

her/his preferences in the user profile that the PA

maintains.

The information stored into the different

repositories of a RAIS network is not accessible to

all the users of the system in the same way. In fact,

it’s important to avoid the access to private

documents and personal files, but also to files

reserved to a restricted group of users (e.g.: the

participants of a project). The RAIS system takes

care of users’ privacy allowing the access to the

information on the basis of the identity, the roles and

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the attributes of the querying user defined into a

local knowledge base of trusted users. In this case, it

is the user that defines who and in which way can

access to her/his information, but the user can also

allow the access to unknown users enabling a

certificate based delegation built on a reputation

network of the users registered into the RAIS

community. For instance, if the user U

enables the

delegation and grants to the user U

the access to its

repository with capabilities C

and U

grants to the

user U

the access to its repository with the same

capabilities C

, then U

can access U

‘s repository

with the same capabilities of U

. The trust delegation

can be useful when the system is used by open and

distributed communities, e.g. to share documents

among the members of an Open Source project.

2.2 Mobile Users Support

People travelling for work may often be in need of

access from a remote system their own computer. In

this situation, a solution could be to install a VNC

server on the desktop computer and to find a system

with a VNC client while travelling. This solution has

the advantage that the user gains the complete

control on his remote PC, but it has also two main

drawbacks: it’s not easy to find computers with

VNC clients available and the VNC connects only to

one computer, not to the whole set of files and

information of a workgroup.

For users that don’t require a complete control

over a remote computer, but need to search and

access a distributed set of documents, we have

included in our system a remote search feature. The

user can ask his/her PA to create a PPA on a

pluggable device, e.g., an USB key or a removable

hard disk. The PA copies on the device the RAIS

run-time, the PPA and the authentication key shared

by the PPA and the PA itself. When the user inserts

the pluggable device on another computer, he can

immediately launch his PPA and connect to its

corresponding PA.

Therefore, the way of using the RAIS system is

analogous to the situation in which the user works

on her/his own computer, except for the interactions

between the PPA and the PA, that, however, are

transparent to the user. In fact, at the initialization,

the PPA sends an authentication key to the PA. If the

key matches those of the PA, the user can provide

his/her username and password and enter the system

(step that must be done by the user when she/he uses

the RAIS system from her/his own computer too).

After these two steps, the PPA acts as a simple

proxy of the remote PA.

3 RAIS DEVELOPMENT

COMPONENTS

The RAIS system has been designed and

implemented taking advantage of agent, peer-to-

peer, information retrieval and security management

technologies and, in particular, of three main

software components: JADE, JXTA (Gong, 2001)

and Google Desktop Search.

RAIS agent platforms have been realized by

using JADE: JADE (Java Agent Development

Framework) is probably the most known agent

development environment enabling the integration

of agents and both knowledge and Internet-oriented

technologies. Currently, JADE is considered the

reference implementation of the FIPA (Foundation

for Intelligent Physical Agents) specifications. In

fact, it is available under an LPGL open source

license, it has a large user group, involving more

than two thousands active members, it has been used

to realize real systems in different application

sectors, and its development is guided by a

governing board involving some important industrial

companies.

The JADE development environment does not

provide any support for the realization of real peer-

to-peer systems because it only provides the

possibility of federating different platforms through

a hierarchical organization of the platform directory

facilitators on the basis of a priori knowledge of the

agent platforms addresses. Therefore, we extended

the JADE directory facilitator to realize real peer-to-

peer agent platforms networks thanks to the JXTA

technology and thanks to two preliminary FIPA

specifications for the Agent Discovery Service and

for the JXTA Discovery Middleware.

JXTA technology (Gong, 2001) is a set of open,

general-purpose protocols that allow any connected

device on the network (from cell phones to laptops

and servers) to communicate and collaborate in a

peer-to-peer fashion. The project was originally

started by Sun Microsystems, but its development

was kept open from the very beginning. JXTA

comprises six protocols allowing the discovery,

organization, monitoring and communication

between peers. These protocols are all implemented

on the basis of an underlying messaging layer, which

binds the JXTA protocols to different network

transports.

FIPA has acknowledged the growing importance

of the JXTA protocols, and it has released some

specifications for the interoperability of FIPA

platforms connected to peer-to-peer networks. In

particular, in the “FIPA JXTA Discovery

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Middleware Specification” a Generic Discovery

Service (GDS) is described, to discover agents and

services deployed on FIPA platforms working

together in a peer-to-peer network. RAIS integrates

a JXTA-based Agent Discovery Service (ADS),

which has been developed in the respect of relevant

FIPA specifications to implement a GDS. This way,

each RAIS platform connects to the Agent Peer

Group, as well as to other system-specific peer

groups. The Generic Discovery Protocol is finally

used to advertise and discover df-agent-descriptions,

wrapped in Generic Discovery Advertisements, in

order to implement a DF service, which in the

background is spanned over a whole peer group.

Different techniques and software tools can be

used for searching information in a local repository.

If the information is stored in form of files, the

Google desktop search system can be considered a

suitable solution because Google provides an SDK

for developing plug-ins based on its desktop search

system. The API that comes with the SDK uses

COM objects, so it’s not directly available for JAVA

development, but a bridge between the API and

JAVA is provided by the Open Source project

GDAPI. Google desktop search indexes the content

of the files of a local drive in a way similar to the

Google Web crawler, providing a searching engine

fast, effective and with the support for a wide range

of file formats.

As introduces before, authentication and

authorization are performed on the basis of the local

knowledge base of trusted users, though they can be

delegated to external entities through an explicit,

certificate based, delegation. In this sense, the

system completely adheres the principles of trust

management. The definition of roles and attributes is

also made in a local namespace, and the whole

system is, in this regard, completely distributed.

Local names are distinguished by prefixing them

with the principal defining them, i.e., an hash of the

public key associated with the local agent platform.

Links among different local namespace, again, can

be explicitly defined by issuing appropriate

certificates. The theory of RAIS delegation

certificates is founded on SPKI/SDSI specifications

(Ellison et al., 1999), though the certificate encoding

is different. As in SPKI, principals are identified by

their public keys, or by a cryptographic hash of their

public keys. Instead of s-expressions, RAIS uses

XML signed documents, in the form of SAML

assertions, to convey identity, role and property

assignments. As in SPKI, delegation is possible if

the delegating principal issues a certificate whose

subject is a name defined by another, trusted,

principal. The latter can successively issue other

certificates to assign other principals (public keys) to

its local name. In this sense, local names act as

distributed roles (Li et al., 2003).

Finally, the extraction of a digest for each search

result is required to avoid the presentation of

duplicate results to the user. This feature is provided

by a Java implementation of the hash function MD5

(Rivest, 1992).

4 CONCLUSIONS

In this paper, we presented a peer-to-peer multi-

agent system, called RAIS (Remote Assistant for

Information Sharing), supporting the sharing of

information among a community of users connected

through the internet.

RAIS is implemented on the top of well known

technologies and software tools for realizing: i) the

agent platforms, i.e., JADE, ii) the peer-to-peer

infrastructure, i.e., JXTA, iii) the searching of

information into the local repository, i.e., Google

Desktop Search, and iv) the authentication and

authorization infrastructure, i.e., SPKI/SDSI

specifications and the SAML assertions. Therefore,

RAIS can be considered something more than a

research prototype that couples the features of Web

searching engines and of peer-to-peer systems for

the sharing of information. First, RAIS improves the

security rules provided to check the access of the

users to the information. In addiction, it offers a

similar search power of Web search engines, but

avoids the burden of publishing the information on

the Web and guaranties a controlled and dynamic

access to the information. Moreover, the agent based

implementation simplifies the realization of three

main features of the system: i) the filtering of the

information coming from different users on the basis

of the previous experience of the local user, ii) the

pushing of the new information that can be of

possible interest for a user, and iii) the delegation of

authorization on the basis of a network of reputation

built by the agents of the system on the community

of its users.

A first prototype of the RAIS system has already

been completed and experimented. The prototype

includes all basic features and a graphical user

interface simplifies the interaction between the user

and the system (see figure 2).

Practical tests on the first prototype were done

installing the system in different labs and offices of

our department asking some students and colleagues

to use it for sharing and exchanging information.

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151

Moreover, we tested the system setting some

computers of a Lab with different access policies

and distributing information on their repositories to

have different copies of the same information on

different computers. The tests covered with success

all system features: basic research, user defined

policies, results filtering, duplicate results

management and remote search through a proxy

personal agent. The tests results were fully

satisfactory and, in particular, the involved users

were interested in continuing its use for supporting

their work activities. The successful experimentation

encouraged us in the further development of the

system and we are currently working on studying the

best way for introducing new types of information

that can be managed (e.g., information stored into

databases) and for including new techniques for the

searching of such information (e.g., semantic Web

techniques).

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Figure 2: RAIS search graphical user interface.

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