Nessun titolo diapositiva

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A distributed agent architectureand case-based
approachfor information system integration
Computer Science Institute University of Ancona
Loris Penserini (pense_at_inform.unian.it)
In collaboration with
Maurizio Panti (panti_at_inform.unian.it) Luca
Spalazzi (spalazzi_at_inform.unian.it)
(these slides are available at
http//www.cs.toronto.edu/mkolp/tropos/)
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Motivation
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 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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Summary
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JEAPFIPA
FIPA Reference Model
Agent Platform (AP) architecture.
AP 1
AP 2
?
?
DF
DF
AMS
AMS
ACC
ACC
Agents
Agents
The network
IIOP
IIOP
IIOP
?
ACC
AMS
DF
Agents
AP 3
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JEAPFIPA
Communication Protocol
FIPA Specification
FIPA defines two types of communication

• Intra-platform

No constraints

• Inter-platform

Internet Inter-ORB Protocol
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.
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JEAPFIPA
Communication Protocol
AP prototype implementation
Intra-platform protocol IIOP

• IIOP is a well known standard.
• Code Portability.
• ACC is simpler.

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JEAPFIPA
Communication Protocol
AP prototype implementation CORBA mechanisms

• Interoperable Object Reference (IOR)

• Transient Name Service (TNS)

Wide compatibility with other FIPA compliant
platforms.
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JEAPFIPA
Agent Communication Channel (ACC) and Agent
Management System (AMS)
FIPA Specification
ACC and AMS strictly interact each other.
ACC supports two kinds of request

• implicit ACC request

• explicit ACC request (forward action)

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JEAPFIPA
ACC and AMS
Example
A second source of overload is the task that ACC
must do for explicit requests
(request sender agent_i_at_iiop//192.168.1.1800
/acc receiver acc_at_iiop//192.168.1.1800/acc
language sl0 ontology fipa-agent-management
protocol fipa-request content (action
acc_at_iiop//192.168.1.1800/acc (forward
(MESSAGE) )) reply-with 0)
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JEAPFIPA
ACC and AMS
Agent_j
ACC
AMS
Agent_i
1 request for Agent_j
2 request
3 agree
4 authenticate
5 inform
6 request from Agent_i
7 agree for Agent_i
8 request
9 agree
10 authenticate
11 inform
12 agree from Agent_j
13 inform done for Agent_i
14 request
15 agree
16 authenticate
17 inform
18 inform done from Agent_j
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JEAPFIPA
ACC and AMS
AP prototype implementation
ACC and AMS are realised as a single agent

• It removes the interaction between ACC and AMS.

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

• It is still FIPA compliant.

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JEAPFIPA
ACC and AMS
AP prototype implementation
We only use implicit requests.

• It reduces the overload for the ACC.

• It is still FIPA compliant.

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JEAPFIPA
Directory Facilitator (DF)
FIPA Specification
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).
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JEAPFIPA
FIPA Platforms and Domains
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JEAPFIPA
Directory Facilitator (DF)
AP prototype implementation
Specification are not clear on what default DF
can contain and which kind of service-name it
must use.
default DF
Service Type Level
FIPA-DF
FIPAACC
FIPA AMS
Service Name Level
Railway
Airport
Agent DF Level (GUID)
DF_j
DF_k

DF_i
Logic structure of the default DF.
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JEAPFIPA
Directory Facilitator (DF)
AP prototype implementation example
A possible situation in which Agent_i would like
to use a service that can perform the Wrapper_i,
but at the begin Agent_i doesnt know that.
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JEAPFIPA
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.

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DCBR approach
Project Overview
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CBR approach
Query Representation Case Memory
Example
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CBR approach
Local 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
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CBR approach
Local Query Rewriting
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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DCBR approach
Distributed Query Rewriting
Principal Cooperation Strategies
Partners
Answers
Queries
Mediators
Sources
Original
Rewritten
Rewritten
Data
all, the newer, the older, ...
the whole query, its components, ...
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DCBR approach
Distributed Query Rewriting
A first strategy the Mediator cooperates with
other mediators, send them the original query,
and asks for receiving the rewritten query.
First consideration
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
redundancy
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DCBR approach
Distributed Query Rewriting
A first strategy the Mediator cooperates with
other mediators, send them the original query,
and asks for receiving the rewritten query.
Second consideration
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
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DCBR approach
Distributed Query Rewriting
A second strategy the Mediator cooperates with
information sources, sends them the original
query, and receives the rewritten query.
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
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DCBR approach
Some Considerations
Notation Sol (Q) the solution of Q (problem)
respect the source S --gt rewritten I (Sol
(Q)) the interpretation of the solution of Q
both respect the source S --gt data
S
S
S
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Mediator 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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Mediator Prototype
Case Memory Organization
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Mediator Prototype
Failure in Retrieval
Different cases of failure during retrieval
- in reuse - in evaluation (partial or total) -
by the user feedback
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Mediator Prototype
Session Example
failure in reuse
Agent i
Mediator
Wrapper 1
Wrapper 2
1 solution requests to mediator
2 It checks in its knowledge
ð
OK

Wrapper interrogation
3.1 request to wrapper 1
solve
4.1
3.2 request to wrapper 1
solve
4.2
3.3 request to wrapper 2
4.3 solve
5.1 data
partial failure in evaluation
5.2 failure
5.3 data
6 Case Memory update
7.1 data
user feedback
7.2 failure
7.3 data
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Mediator Prototype
Cooperation Strategies
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Mediator Prototype
Cooperation Example
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Mediator Prototype
Strategies Evaluation
The tests have evaluated, for each strategy,
these kinds of problems
- knowledge growing - knowledge redundancy -
response time - network overload
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Mediator Prototype
Strategies 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
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Mediator Prototype
Strategies Evaluation Results
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Mediator Prototype
Strategies Evaluation Results
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Mediator Prototype
Strategies Evaluation Results
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)
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Future 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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References
- 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,
1014 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.