An Evolutional Cooperative Computation Based on Adaptation to Environment Naoyasu UBAYASHI and Tetsuo TAMAI Graduate School of Arts and Sciences University of Tokyo APSEC’99

Overview １． Introduction ２． Environment Adaptation Model ３． Advanced topics using Environment Adaptation Model ４． Related Works ５． Conclusion

Introduction

Background Recently, software systems that reside in network environments are spreading rapidly. These systems has properties such as distributed, mobile, dynamic, adaptable. *These kinds of software systems are composed of a number of distributed objects that may change their locations dynamically. *These objects change their functions dynamically to adapt themselves to their external environments. Constructions of these kinds of systems are considered as very hard and difficult works.

Illustration of Recent software systems object collaboration

Problems It is difficult to describe functions that are dispersed in a number of distributed objects in current object oriented programming languages. These functions are implemented by collaborations among objects. -- not implemented by a single object! gives abstraction mechanisms for collaborations It is difficult to describe dynamic evolution in current object oriented programming languages. gives abstraction mechanisms for evolution

Target (1) Presents a framework that an object evolves through collaborations. an object acquires or discards functions and attributes dynamically Collaborations a number of objects engaging in their own roles send messages to each other and perform a job that cannot be executed by a single object Evolution

Target (2) gives mechanisms for abstracting collaborations among objects mechanisms for creating collaboration parts mechanisms for synthesizing collaboration parts mechanisms for object evolution mechanisms for integrating collaborations with evolution

Environment Adaptation Model

Basic Concepts role environment role environment (collaboration filed) bind unbind object Multiple adaptation

Model Constructs (1) Environment - logical field where a group of objects collaborate with each other - composed of environment methods/attributes, role definitions - aims 1) to give name space 2) to give common methods/attributes 3) to coordinate behaviors of objects in the field 4) to define object behaviors that are available only in the field >> roles Role - composed of role methods/attributes

Model Constructs (2) Evolution - an object joins into an environment and acquires new collaboration functions by bind-operations. the object can collaborate with other objects in the environment role environment bind object Bind-operation message delegation - creates a message delegation path between an object and a role.

Merits 1) gives mechanisms that encapsulate collaboration descriptions among objects into environments and roles. * design methods that abstract collaborations * techniques that construct reusable collaboration components 2) gives evolution mechanisms. * design methods for distributed mobile agent systems -- agents need to change their functions dynamically in order to adapt themselves to their environments.

Example -- Contract Net Protocol （１） task-announcement （２） bid （３） award Role methods Role （ manager ） Role(contractor) （１） （３） （２ ） Environment （ contract-net ） Evolve to manager (bind-operation) object Environment （ contract-net ） Evolve to contractor General contract net protocol Synthesizing simple contract-net environments

Programming Language Epsilon/0 1) Epsilon/0 supports Environment Adaptation Model. - environments, roles and bind-operations are supported as language constructs. 2) Epsilon/0 supports reflection mechanisms. 3) Epsilon/0 is implemented using ABCL/R3 that is a reflective object oriented programming language based on Scheme.

Descriptions of Contract Net Protocol in Epsilon/0 > contract-net > manager start() bid() > contractor task-announcement() award() execute-task() manager contractor object task-announcement bid award bind execute-task (delegate!!)

(define-context contract-net () … common attributes) (define-context-method contract-net (common method….)) Descriptions of contract-net environment Environment class

(define-role contract-net manager () condition-shown-by-manager) (define-role-method contract-net manager (start self) (let ((contractor-list (get-role (context-of self) ‘contractor)))... broadcasts a task-announcement message to all roles that are contained in the contractor-list)) (define-role-method contract-net manager (bid self a-contractor a-condition-shown-by-contractor)... stores a bid-information (if (bidding is finished) (award (select-contractor self) self))) Descriptions of manager role Role class

Descriptions of contractor role (define-role contract-net contractor () condition-shown-by-contractor) (define-role-method contract-net contractor (task-announcement self a-manager a-condition-shown-by-manager) (if satisfies conditions) (bid a-manager self condition-shown-by-contractor))) (define-role-method contract-net contractor (award self a-manager) (execute-task self)) 1) execute a method of an object bound with this role 2) execute-task is interface for binding with an object

Execute a program (define contract-A (make-context contract-net)) (define contract-B (make-context contract-net)) (define-class person () name) (define-method person (execute-task …)) (define a-person (make person)) ;; evolves to manager (bind contract-A a-person (make-role contract-net manager contract-A)) (start (search-role a-person contract-A)) ;; evolves to contractor (bind contract-B a-person (make-role contract-net contractor contract-B)) (start (search-role a-person contract-B)) behaves different roles contract-A contract-B evolves to manager evolves to contractor

Advanced topics using Environment Adaptation Model

Advanced topics 1) Autonomous evolution using reflection mechanisms 2) Reusable collaboration components Environment Adaptation Model presents nice features for software constructions

Autonomous Evolution evolution Contract-net protocol environment manager contractor Nancy John Steve Contract-net protocol environment manager

Reflective Architecture object Meta object Each object can have its own engine Meta level Base level Engine of autonomous action (replaceable) Engine of autonomous action (replaceable) Engine of autonomous action (replaceable) object Action strategies --- plans for environment adaptations

Reusable Collaboration Component Construction Mechanism (1) *It is difficult to abstract execution information such as number/kind/reference of objects that participate in collaborations. *This information changes dynamically and cannot be defined statically. Problems...

Reusable Collaboration Component Construction Mechanism (2) Abstracts execution information using refection mechanisms ｇｅｔ－ａｌｌ－ｃｏｎｔｅｘｔ ｇｅｔ－ａｌｌ－ｃｏｎｔｅｘｔｎａｍｅ ｃｏｎｔｅｘｔ－ｏｆ ｇｅｔ－ｒｏｌｅ ｇｅｔ－ａｌｌ－ｒｏｌｅ ｇｅｔ－ａｌｌ－ｒｏｌｅｎａｍｅ ｂｏｕｎｄ？ Meta information environment Meta information role method access Collaboration field Name space Presents built-in functions

Related Works

Researches for abstracting collaborations 1) Aspect Oriented Programming (G.Kiczales, et al.) propose a programming paradigm that a system is divided into a number of aspects. 2) Role based design method (M.VanHilst, D.Notkin 1996) propose an idea of role components that are described by C++ templates. 3) Coordinated Roles (Juan M.Murillo, et al. 1999) * Dynamic evolution is not so emphasized.

Conclusion

Summary We proposed mechanisms for abstracting collaborations among objects mechanisms for creating collaboration parts mechanisms for synthesizing collaboration parts mechanisms for object evolution mechanisms for integrating collaborations with evolution

Future Works applies environment adaptation model to distributed mobile agent systems to familiar languages such as Java...

Base Level Descriptions ;; Class definition (define-class person () name money) (define-method person (execute-task self)...) (define-method person (life self job) (meta-life (meta-of self) job)) ;; Start autonomous actions (define taro (make person :name "Taro Yamada" :metaobject-creator make-taro-meta)) (life taro a-job) Specifies meta object Calls meta object

Meta Level Description ;; Descriptions for adaptation strategies (meta (define-class taro-meta (metaobject)) (define (make-taro-meta class slots evaluator options) (make taro-meta :class class :slots slots :evaluator evaluator :lock (make-lock))) (define-method john-meta (meta-life self job) (future-to-base... divides a job into a number of sub-tasks.... repeats the following activities. (let ((env (get-all-context))) (begin... searches contract-net environments where he can join as a manager. (bind selected-contract-net (den-of self) selected-manager) (start (search-role (den-of self) selected-contract-net)) )))) 1) Searches target environments 2) Searches target roles that exist in the selected environment 3) Binds itself with the selected role ( evolution ! ) Design Pattern If this part is changed, a number of adaptation strategies can be implemented! ! Open Implementations