An Evolutional Cooperative Computation Based on Adaptation to Environment

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

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

3. Introduction

4. 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 ofdistributed 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.

5. Illustration ofRecent software systems object collaboration object object

6. 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

7. Target (1) Presents a framework that an object evolves through collaborations. 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 an object acquires or discards functions and attributes dynamically

8. 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

9. Environment Adaptation Model

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

11. 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

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

13. 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.

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

15. 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.

16. << Environment >> contract-net contractor contractor contractor << Role >> manager start() bid() Descriptions of Contract Net Protocolin Epsilon/0 task-announcement bid manager award execute-task (delegate!!) bind << Role >> contractor object task-announcement() award() execute-task()

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

18. Descriptions of manager role Role 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)))

19. 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

20. 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)) contract-B contract-A evolves to contractor evolves to manager behaves different roles

21. Advanced topicsusing Environment Adaptation Model

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

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

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

25. Reusable Collaboration ComponentConstruction Mechanism (1) Problems ... *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.

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

27. Related Works

28. 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.

29. Conclusion

30. 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

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

32. 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) Calls meta object Specifies meta object

33. 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)) )))) Design Pattern 1) Searches target environments 2) Searches target roles that exist in the selected environment 3) Binds itself with the selected role ( evolution ! ) If this part is changed, a number of adaptation strategies can be implemented! ! Open Implementations