debugging multi-agent systems using design artifacts: the case of interaction protocols by david...

Debugging Multi-agent Systems Using Design Artifacts:

The Case of Interaction Protocols

By David Poutakidis

Introduction

Agents are softwareDeveloping agents is developing

softwareNeed appropriate design

methodologies and tools (Prometheus)Debugging and Testing are an

important part of any system development.

Debugging is important.

Up to 50% of the total cost/time of development

Much of this time is spent trying to: Locate bugs Determine the cause of a problem

Debugging problem exacerbated by the flexibility and complexity of agent systems

Current Debugging Techniques

Information gathering and visualisation Filtering applied Color Coded messages displayed at

runtimeLimitations

Too much information to digest No process for choosing the info to display Relies on programmer interpreting

message flow properly

Our Approach: Make use of Design Documents

During design, documents are produced: which represent the developers description

of the system that describe how the system should operate that guide the programmers during coding

Design Artifacts: interaction protocols, interaction diagrams,

scenario diagrams, capability diagrams, plan descriptors, etc

Central Thesis:

is that the design documents and system models developed when following an agent based software engineering methodology can be valuable resources during the debugging process and should facilitate the automatic or semi-automatic detection of errors.

Interaction Protocols

Capture interaction patterns between agents

Allow choices and describe all allowable interactions

Existing protocol’s developed, eg FIPA (based on AUML)

Buy bookBuy book

Delivery info.Delivery info.

Delivery choiceDelivery choice

Card detailsCard details

Card details requestCard details requestCard detailsCard details

ApprovalApprovalThanksThanks OrderOrder

User Shop ass. Warehouse Cashier

Credit check requestCredit check request

Details requestDetails request

Use case:

1. Customer orders book

2. Customer specifies delivery

3. Shop ass. Obtains & checks credit details

4. Shop ass. thanks customer and places order

Use Case and Interaction Diagram

Merchant Bank

x

Credit check request (CCR)

Card details request (CDR)

Card details (CCD)

Approve

Reject-2

Fraud

Reject-1

M1

M2

M3

M4

M5

M6

B1

B2

Debugging with Interaction Protocols

Agent AgentMessages

Debugger

User

AUML not suitable for debugger

AUML not used internally by the debugger AUML is not precisely defined, no formal

semantics decouple the underlying representation to

allow for future versions of AUML or other notations altogether.

We use equivalent Petri Nets internally Clear formal semantics, algorithms and tools

for checking properties (liveness, deadlock…)

Petri Nets Explained

•Consists of Places (depicted as circles) and Transitions depicted as squares.

•Places and Transitions linked by arrows.

•Places can contain tokens which indicate it’s marking and the state the net is in.

Before Firing

After Firing

Converting AUML protocol to a Petri net equivalent.

a aP Q

P a

QQ

P a

Translating AUML Connectors

a

b

AUML: Selection

Petri net: Selection

P

P

Q

Q

a b

R

R

M1

CCR

B1

CDR

M2

CCD

B2

Fraud

M6

M3

M5M4

B2’’B2’

Reject-2

Reject-1

Approve

Bank

x

Credit check request (CCR)

Card details request (CDR)

Card details (CCD)

Approve

Reject-2

Fraud

Reject-1

M1

M2

M3

M4

M5

M6

B1

B2

Merchant

Reject-2

Reject-1

Approve

M1

CCRB1

CDR

M2

CCD

M6

B2

M3

B2’ B2’’

M4 M5

Execution of the Debugging Agent

Repeat:

1. Receive message m

2. Check m against existing protocol instances

3. Fire the Petri Net(s)

4. Examine the Petri Net(s) for erroneous conditions.

Reject-2

Reject-1

Approve

M1

CDR

M2

CCD

M6

B2

B2’ B2’’

M4 M5

M3

CCR

Consider the following sequence of messages:

•Merchant to bank: CCR

•New protocol instance created and token placed on M1

•Token placed on CCR

•Fire net

B1

Reject-2

Reject-1

Approve

M1

CDR

M2

CCD

M6

B2

B2’ B2’’

M4 M5

M3

CCR





•Fire net

•Bank to Merchant: CDR

•Token placed on CDR

•Fire net

B2

Reject-2

Reject-1

Approve

M1

CDR

M2

CCD

M6

B2

B2’ B2’’

M4 M5

M3

CCR





•Fire net



•Fire net

•Merchant to Bank:CCD•Token placed on CCD

•Fire Net

Reject-2

Reject-1

Approve

M1

CDR

M2

CCD

M6

B2

B2’ B2’’

M4 M5

M3

CCR





•Fire net

•Merchant to Bank:CCD

•Token placed on CCD

•Fire Net

•Bank to Merchant: Approve•Token placed on approve

•Fire net

Reject-2

Reject-1

Approve

M1

CDR

M2

CCD

M6

B2

B2’ B2’’

M4 M5

M3

CCR




•Merchant to Bank:CCD

•Token placed on CCD

•Fire Net

•Bank to Merchant: Approve

•Token placed on approve

•Fire net

•Bank to Merchant: Fraud•Token placed on Fraud

•Fire Net

Fraud

Reject-2

Reject-1

Approve

M1

CDR

M2

CCD

M6

B2

B2’ B2’’

M4 M5

M3

CCR

Error encountered!!!

•No transition enabled (because there is no token on B2)

•The debugging agent reports a bug: the fraud message was unexpected

Fraud

Future Work

Currently implementing the debugging agent

Provide tool support to automatically convert AUML protocols to Perti nets

Investigate how other design artifacts can be used for debugging