MODELLING OF MOBILE AGENT SYSTEMS USING dynPLA APPROACH Agnė Paulauskaitė-Tarasevičienė Henrikas Pranevičius 1

Mobile agent systems – variable structure systems Models of variable structure systems define the systems, which in time change not only their state but the structure as well. 1. Intelligent systems, 2. Biological systems, 3. Distributed network systems,.. The structure of system models can change by: o adding new components, o adding new couplings between system components, o removing existing components, o removing couplings, o moving components from one location to another. 2

Multi-Agent Systems (MAS)  Multi-agent systems Adaptation, Cooperation, Mobility, Autonomy,..  Mobile agents because of their ability to migrate, are used in the wide range of applications: systems intellectualization, distributed computer network management, m-commerce,... 3

Formal methods Variable structure systems are complex and mostly critical therefore it is beneficial to describe them using formal methods (Petri Nets, DEVS,  -calculus), which enable mathematical description and verification. Dynamic DEVS notations:  dynDEVS (A. M. Uhrmacher),  ML-DEVS (A. M. Uhrmacher),  M-DEVS (J.H. Kim, T.G. Kim). 4

A Piece Linear Aggregate method Piece–Linear Aggregates (PLA) (H. Pranevičius) method is used for complex systems formalization, verification and simulation. The PLA is taken as an object defined by:  a state Z,  input signals X,  output signals Y.  transition operators H,  output operators G. 5

Purpose of research 6  Purpose – to present the new concept for modelling the mobile agent systems using aggregate method with included Abstract Data Types.

Content 7 Dynamic PLA (dynPLA) structurePossible structural changes in dynPLA Definition of abstract data types describing aggregate system structural changes Formal Object-Z description of included ADTApplication: mobile agent-based e-commerce system model

Dynamic PLA - dynPLA 1) Structural changes in dynPLA model are performed by adding and removing the elements of variable sets.  the removal of input signal  the addition of input signal 2) The external aggregate(s) is excluded in the system that would be responsible for the execution of structural changes. 8 A1A2 A5 A3 A4 A1

Structural changes in dynPLA In dynPLA aggregate system five types of structural changes are excluded. 1. A ddition of new link; 2. Removal of link 3. Addition of aggregate 4. Removal of aggregate 5. Aggregate migration form one system to another A1A2 A1A2 A1 Anew A1 A2 A1A2A1 A2 9

Abstarct Data Types in dynPLA Abstract Data Types (ADT) are used for definition of structural change operations in dynPLA.  ADT structure –aggregate system.  ADT operations – structural changes in aggregate system. Operations: 1. AddAgR 2. RemoveR

ADT Operations (1)  Mobile agent creation: Operation AddAgR, which adds a new aggregate with links, is used to describe the creation of new mobile agents.  Mobile agent deletion: Operation RemoveAg, which eliminates the aggregate with its entire links, is used to describe MA deletion. 11 Aggregate system

ADT Operations (2) 12  Mobile agent migration: To describe agent transportation, the operation TransportAgR is used, which transports the denoted aggregate from one aggregate system to another one, adding the required links in a new place.  Mobile agent cloning: Operation ClounAg is used to describe mobile agent cloning process, which creates the aggregate copies in an aggregate system. Aggregate system

Formal description of included ADT in dynPLA To define ADT in dynPLA, Object-Z specification language has been used.  unambiguous definition of structural change operations,  the preconditions, which have to be met in order to properly perform the structural changes in dynPLA model,  ADT definition in object oriented manner. 13 Ag_SyS AddAgR, RemoveAg, TransportAgR

AddAgR operation 14 A1Anew y1x1 Ag_Sys

Included ADT advantages Defined ADT allow:  to avoid the descriptions of many additional actions used in fulfillment any structural change and thereby present the specification in shorthand way;  to produce an unambiguous statement for these actions needed while performing the structural changes;  to avoid specification errors, since one can manipulate only with operations that are defined in advance. 15

Example: Application of mobile agent-based e- commerce system  User, willing to find a certain product on the internet, communicates to a User Interface Agent (UIA).  UIA creates a MA and delegates the task to it.  MA migrates across the internet to the Data Directory (D).  MA collects all the information from the providers and returns it to UIA, which, in turn, deletes the mobile agent after getting its response. 16 Mobile agent

Mobile agent migration patterns 17  Two mobile agent migration ways are analyzed in this example:  1. Itinerary – the mobile agent visits all suppliers from the list and returns to the host server after visiting the last supplier;  2. Branching – after getting the list of providers the mobile agent clones itself according to the number of providers. Every cloned agent visits the provider assigned to it and moves to the host with gathered information.

Aggregate schema of mobile agent-based e-commerce system 18

Description of mobile agent-based e-commerce model structural changes Structural changes of model are described using such ADT operations:  AddAgR – mobile agent creation;  TransportAgR – mobile agent migration;  ClounAg – mobile agent cloning process, when it migrates in branching pattern;  RemoveAg – mobile agent deletion. 19

Simulation in JADE 20  The model was implemented in JADE software platform.  JADE has an integrated mobile agent platform.  Agent migration is realized using FIPA mobile requests protocol.  JADE provides a cloning mechanism that takes snapshot copy of an existing agent.

Experiment results 21

Conclusions and Remarks  dynPLA model with included ADT for implementation of MA creation, removal, migration and cloning operations can be used to create various MA systems such as intellectual, distributed network and other.  The usage of ADT for description of mobile agents systems allows to significantly reduce the size of formal specification, since there is no need to additionally specify the operations that alter the system model. In addition, there is a possibility to extend the specification by introducing the new operations if needed, that greatly increase the flexibility of structure-change modeling. 22

Thank you 23