loris penserinicomputer science institute - university of ancona 1 a distributed agent architecture...

Loris Penserini Computer Science Institute - University of Ancona

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A distributed agent architecture

and case-based approach

for information system integration

A distributed agent architecture

and case-based approach

for information system integration

Computer Science Institute

University of Ancona

In collaboration with:

Loris Penserini ([email protected])

Maurizio Panti ([email protected])

Luca Spalazzi ([email protected])

(these slides are available at: http://www.cs.toronto.edu/~mkolp/tropos/)


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MotivationMotivation

In a network environment the principal problems of Information System Integration are:

- distribution: the needing of sharing sources between LANs and/or WANs

- dynamism: new sources can be inserted or deleted, the schemas can be modified and so on

- heterogeneity: discrepancies in physical, logical, and conceptual levels


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Work PurposeWork Purpose

- to use an Agent Platform to face the distribution

- to solve dynamic problems by a Distributed CBR approach

- to adopt a Mediator architecture to face the heterogeneity

- to evaluate both the efficacy and the efficiency of the Mediator cooperation strategies by a prototype implementation


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SummarySummary

AgentManagement

SystemDirectory

Facilitator

Agent Communication Channel

Agent

Software

* Agent Platform architecture FIPA compliant

Mediator1Case

Memory1

* Mediator agent that uses a Distributed CBR

Wrapper1

db1

Wrapper2

db2

* Mediator prototype and Cooperation Strategies

Mediator2

Case Memory2


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Agents

AP 1 AP 2

AP 3

The network

Agent Platform (AP) architecture.

DF

AMS

ACC

IIOP

IIOP IIOP

FIPA Reference ModelFIPA Reference Model

?

Agents

ACC

AMS

DF

?

Agents

DF

AMS

ACC

?

JEAP&FIPA


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Communication ProtocolCommunication Protocol

FIPA defines two types of communication:

• Inter-platform

• Intra-platform

Internet Inter-ORB Protocol

No constraints

CORBA allows several mechanisms in order to locate distribute objects, which are incompatible each other, but FIPA does not specify which one must be used.

FIPA Specification:

JEAP&FIPA


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AP prototype implementation:

Intra-platform protocol: IIOP

• IIOP is a well known standard.

• Code Portability.

• ACC is simpler.

JEAP&FIPA


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AP prototype implementation: CORBA mechanisms

Wide compatibility with other FIPA compliant platforms.

• Interoperable Object Reference (IOR)

• Transient Name Service (TNS)

JEAP&FIPA


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ACC and AMS strictly interact each other.

ACC supports two kinds of request:

• implicit ACC request;

• explicit ACC request (forward action);

Agent Communication Channel (ACC)

and Agent Management System (AMS)

Agent Communication Channel (ACC)

and Agent Management System (AMS)

FIPA Specification:

JEAP&FIPA


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ACC and AMSACC and AMS

(request :sender agent_i@iiop://192.168.1.1:800/acc :receiver acc@iiop://192.168.1.1:800/acc :language sl0 :ontology fipa-agent-management :protocol fipa-request :content (action acc@iiop://192.168.1.1:800/acc (forward (MESSAGE) )) :reply-with 0)

A second source of overload is the task that ACC must do for explicit requests:

Example:

JEAP&FIPA


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10: authenticate

8: request

3: agree

2: request

5: inform

4: authenticate

7: agree for Agent_i

Agent_j ACC AMSAgent_i

1: request for Agent_j

6: request from Agent_i

9: agree

11: inform

13: inform done for Agent_i

16: authenticate

14: request

15: agree

17: inform18: inform done from Agent_j

12: agree from Agent_j

JEAP&FIPA


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• It removes the interaction between ACC and AMS.


ACC and AMS are realised as a single agent:

• It does not decrease fault-tolerance capability of the platform.

• It is still FIPA compliant.


JEAP&FIPA


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We only use implicit requests.



• It reduces the overload for the ACC.

• It is still FIPA compliant.

JEAP&FIPA


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Directory Facilitator (DF) Directory Facilitator (DF)

The DF provides a yellow-pages service.

The agents registered at the DF are classified by means of service-type and service-name.

A Domain is the set of all the agents registered at the DF.

The Agent Universe is the union of all the domains.

Each Agent Platform must have at least one DF (the default DF).

FIPA Specification:

JEAP&FIPA


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FIPA Platforms and Domains FIPA Platforms and Domains JEAP&FIPA


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Specification are not clear on what default DF can contain and which kind of service-name it must use.

Logic structure of the default DF.

Agent DF Level (GUID)

Service Type Level

Service Name Level

default DF

FIPA–ACC FIPA-DF FIPA – AMS

Railway

DF_j DF_k

…

Airport

DF_i

JEAP&FIPA


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AP prototype implementation: exampleA possible situation in which Agent_i would like to use a service that can perform the Wrapper_i, but at the begin Agent_i doesn’t know that.

6:Results 5:Invoke the service

3:Search for an agent

1:Search for a domain

Agent_k

Agent_i

Agent Platform

DF Default

DF_j

2:Answer with DF_j address

4:Answer with agent address (Agent_k)

JEAP&FIPA


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Some Remarks on FIPA Some Remarks on FIPA

FIPA is an effective solution to agent cooperation in heterogeneous and distributed environments.

Nevertheless FIPA specification are not clear:

• Communication protocols: intra-platform and inter-platform;

• ACC and AMS: they have a strictly interaction and ACC is overburdened by the forward action;

• Default DF: its role and organisation are not clear.

JEAP&FIPA


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Project OverviewProject Overview

DCBR approach


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Query Representation: Case MemoryQuery Representation: Case Memory

Example:

CBR approach


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Local Query Rewriting: TerminologyLocal Query Rewriting: Terminology

The problems (queries, Q) are classifies according to subsumption relation.

In particularly, in this work, Q is decomposed and then classified.

For example:

CBR approach


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Local Query RewritingLocal Query Rewriting

CBR approach

Query Evaluation: the Mediator sends a decomposition of Q to the related information source and wait for their answers.

Local Failure in Query Reuse: the Mediator is not able to rewrite Q since its case memory contains no past cases that can be used to do it. For example, it is the first time that the consumer formulates such a query, i.e., the consumer has a new information need.

Local Failure in Query Evaluation: the Mediator sends a rewritten query to related sources and receives at least an empty answer. This means that the case memory of the mediator is not updated (an information source has been removed from system or changed its schema).


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Distributed Query RewritingDistributed Query Rewriting

Principal Cooperation Strategies:

DCBR approach

Partners Answers Queries

Mediators Sources

all, the newer, the older, ...

Original Rewritten Rewritten Data

the whole query, its components, ...


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A first strategy: the Mediator cooperates with other mediators, send them the original query, and asks for receiving the rewritten query.

DCBR approach

Theorem. Let M, N be two mediators such that M interacts with N when M fails. Let Cn(M) be the case memory of M after n interactions with N. Let Cn(N) be the case memory of N such that it does not change while N interacts with M. Then

1))((

))()((lim

NCcard

NCMCncard

n

First consideration

redundancy



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A first strategy: the Mediator cooperates with other mediators, send them the original query, and asks for receiving the rewritten query.

DCBR approach

Theorem. Let be n information sources. Let V be a view of . Let M, N be two mediators such that M interacts with N when M fails. Let Cn(M) be the mediated schema of M after n interactions with N. Then

Second consideration

decreasenot does ))(

))((lim

Vcard

VMCncardRecall

n

1 to convergenot does ))((

))((lim

MCncard

VMCncardPrecision

n

nSS ,...,1 nSS ,...,1



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A second strategy: the Mediator cooperates with information sources, sends them the original query, and receives the rewritten query.

DCBR approach

Theorem. Let be n information sources. Let V be a view of . V is represented as a case memory that does not change. Let M be a Mediator such that M interacts with when it fails. Let Cn(M) be the case memory of M after n interactions with . Then

1 to converges ))(

))((lim

Vcard

VMCncardRecall

n

nSS ,...,1 nSS ,...,1

nSS ,...,1

nSS ,...,1

1 to converges ))((

))((lim

MCncard

VMCncardPrecision

n



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Notation

Sol (Q) :

the solution of Q (problem) respect the source S --> rewritten

I (Sol (Q)) :

the interpretation of the solution of Q both respect the source S --> data

S

S S

Some ConsiderationsSome Considerations

DCBR approach


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Mediator PrototypeMediator Prototype

Mediator Prototype

- Its language is a restrict set of Sequel Query Language

- It implements a wide set of cooperation strategies

- It collaborates with other mediators and ‘simple’ wrappers

- Its Solution-Analysing and the Case-Memory Updating phases are still user driven


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Case Memory OrganizationCase Memory Organization

Mediator Prototype

PROB:select EmployeeInfo from Employee

SOL:"select EmployeeName from Employees@wrapper1@ iiop:// 129.100.27.30:900/acc" and "select EmployeeAddr from Address@wrapper2@iiop://193.205.128.40:1000/acc"


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Failure in RetrievalFailure in Retrieval

- in reuse

- in evaluation (partial or total)

- by the user feedback

Different cases of failure during retrieval:

Mediator Prototype


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Session ExampleSession Example

Wrapper 1 Wrapper 2

5.3: data

4.1:

2: It checks in its knowledge

OK Wrapper interrogation

Agent i Mediator

5.1: data

7.3: data

3.1: request to wrapper 1

3.2: request to wrapper 1

3.3: request to wrapper 24.2:

4.3: solve

7.1: data

5.2: failure

7.2: failure

6: Case Memory update

1: solution requests to mediator

solve

solve

Mediator Prototype

partial failure in evaluation

failure in reuse

user feedback


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select EmployeeInfo from Employee

Cooperation StrategiesCooperation StrategiesMediator Prototype


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Mediator 1Mediator 1 Mediator 2Mediator 2

W1W1 W2W2 W3W3

1: request

3: data 2: data

2: rewrite

3: data

Cooperation ExampleCooperation Example

Mediator Prototype


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Strategies EvaluationStrategies Evaluation

The tests have evaluated, for each strategy, these kinds of problems :

- knowledge growing

- knowledge redundancy

- response time

- network overload

Mediator Prototype


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Strategies EvaluationStrategies Evaluation

The principals tests consist in five general queries (problems) all performed on the following five different strategies:

Strategy 1: a mediator (M) sends the original query (Q) to another mediator (N) and requests for a rewrite

Strategy 2: M sends a decomposition of Q to N and requests for a rewrite

Strategy 3: M sends to N only the rewrited components of Q that it cannot solve and asks for the data

Strategy 4: M directly sends a decomposition of Q to the wrappers and asks them for the data

Strategy 5: M directly sends only the rewrited components of Q to the wrappers and asks for the data

Mediator Prototype


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Knowledge Growing

0

1

2

3

4

5

6

7

8

9

10

1 2 3 4 5Query

Ca

se N

°

Strategy 1

Strategy 2

Strategy 3

Strategy 4

Strategy 5

Strategies Evaluation: ResultsStrategies Evaluation: Results

Mediator Prototype


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Mediator Prototype

Redundancy Growing

0

1

2

3

4

5

6

1 2 3 4 5Query

Ca

se

N°

Strategy 1

Strategy 2

Strategy 3


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Time Responses (s)S

trat

egie

s

Max Min. Average

Ste

ps

Ser

vice

Mes

sage

sD

ata

Mes

sage

sS

mal

lM

essa

ges

Big

Mes

sage

s

Tot

al

1 84 17 39,0 4 6 5 8 3 11

2 91 46 70,5 4 7 6 10 3 13

3 96 38 69,3 4 5 5 6 4 10

4 127 66 93,8 2 11 4 12 3 15

5 84 47 67,7 2 8 3 9 2 11

Steps: principal phases of a communication (without any FIPA protocols)

Service Messages: they do not contain data (query responses) inside otherwise they should be considered ‘Data Messages’

Small/Big Messages: it is another possible type of messages subdivision based on the content of a FIPA message (e.g. an ‘agree’ message is considered ‘small’, whereas an ‘inform’ messages is big, and so on)


Mediator Prototype


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Future DevelopmentFuture Development

- The designing and developing of a Mediator agent that uses a CBR engine based on DL

- The designing of protocols that automatically choice the best strategy in response to a particular failure

- To consider other useful cooperation strategies

- To apply this architecture in a real case of interest to test its capacity (e.g. some kind of web applications)


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ReferencesReferences

- M. Panti, L. Penserini, L. Spalazzi, S. Valenti, "A FIPA Compliant Agent Platform for Federated Information Systems", International Journal of Computer & Information Science, R. Y. Lee and H. Fouchal (eds), ACIS, 2000.

- C. Cioffi, M. Panti, L. Penserini, L. Spalazzi, E. Tonucci, S. Valenti, ``An Agent-Based Platform for Federated Information Systems: Some Design Issues'', in Proc. of the International Conference on Software Engineering Applied to Networking and Parallel/Distributed Computing (SNPD '00), Reims, France, May 18-21, 2000.

- M. Panti, L. Penserini, L. Spalazzi, ``A Critical Discussion about an Agent Platform based on FIPA Specification'', in Atti dell'Ottavo Convegno Nazionale su Sistemi Evoluti per Basi di Dati (SEBD 2000) , L'Aquila Italia, 26-28 Giugno 2000.

- M. Panti, L. Spalazzi, A. Giretti, “A case-based approach to information integration”, In Proceedings of the 26th International Conference on Very Large Databases, Cairo, Egypt, 10–14 September 2000.

- Foundation for Intelligent Physical Agents, Fipa 2000 Specification. Geneva, Switzerland, October 2000. Available at: http://www.fipa.org/

- E. Plaza, J. L. Arcos, and F. Martìn, “Cooperative Case-Based Reasoning”, In G. Weiss, editor, Distributed Artificial Intelligence meets Machine Learning, Lecture Notes in Artificial Intelligence, Berlin, 1997. Springer Verlag.

- G. Wiederhold, “Mediators in the architectures of future information systems”, in IEEE Computer, vol. 25, N. 3, pp. 38--49, 1992.

loris penserinicomputer science institute - university of ancona 1 a distributed agent architecture...

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