Notion de communauté dans des systèmes distribués de Montréal

21 février 2003Séminaire UQAM

Universitéde Montréal

Notion de communauté dans dessystèmes distribués

Peter KropfDépartement d’informatiqueet de recherche opérationnel

Université de Montréal

21 février 2003Université de Montréal 2

! Common interests! Shared context! Self-organisation! Autonomous individuals/entities

Communities are groups of objects in a sharedcontext. This allows at least a communication witheach other. [DCW 2000: Plaice, Kropf, Unger]

Social aggregates emerging from the Internet whenenough people carry on public discussions longenough and with sufficient human feeling to formwebs of personal relationships [ Howard Rheingold]

CommunitiesCommunities


! How do communities emerge and how can their structuresbe analyzed and modeled?

! Which effects and laws are known from social communitiesand how are these communities structured and reorganized?

! How do cooperation and work division emerge? What does itmean to speak about “communities” within the context ofthe Web (e.g. for data search, network load, structuring ...)?

! How can dynamic changes be considered within acommunity?

! Which advantages and new services can be developed andused?

Peer-to-Peer systems are deployed and workingdistributed communities on the Net

Communities: key issuesCommunities: key issues


Types of P2P systemsTypes of P2P systems

! E-commerce systems– eBay, B2B market places, …

! File sharing systems– Napster, Freenet, Gnutella, Morpheus, KaZaA, AWeb…

! Distributed databases– Mariposa, DNS, …

! Networks, «middleware»– Arpanet, WOS (Web Operating System), JXTA,

Mobile ad-hoc networks (MANET), Multi-agent systems ….

P2P is an application-level internet on top of the Internet

overlay network


SystemSystem ArchitecturesArchitectures

timeHierarchy

Asymmetry

Self-organizationSymmetry

CCCC

M

Music Industry

AA

CCCC

M

MP3

AA

C

C

C

gnutella

A

CCC

CM

Napster

A

A

unidirectional

interactive

Unidirectional/bilateral

multilateral

structure

con

tro

l

Centralization Decentralization


RationaleRationale for WOSfor WOS

The future (present?) of information systems:networked, diverse, numerous, mobile, ubiquitous

! The Web Operating System aims to :– Supply users with adequate tools that allow for the

implementation of specific services and sharingresources

– Provide users with great flexibility in the “semantic” oftheir services.

! Services are volatile:– Services appear, disappear, evolve, etc.– Services and environments have to adapt to their

contexts.

! WOS Vision :– any-time, any-where, any-service.

S. Ben Lamine, P.G. Kropf and J. Plaice, <<Problems of Computing on the Web>>, High Performance Computing Symposium 97,A. Tentner, ed., The Society for Computer simulation International, Atlanta, Georgia, USA, pp. 296--301, April 1997.


RationaleRationale for WOSfor WOS

WOSMiddleware/Services

Self-configuring networks of mobile and stationarydevices form communities


TheThe Nature of WOSNature of WOS

! Each node is client andserver at the same time

! The nodes may formcommunities

! Each node maintainsinformation warehouses

! Uniform communicationlayer

! Minimal set of services– Search and discovery– Warehouse management

WO

SC

omm

unic

atio

nLa

yer

Remote ResourceControl Unit

(RRCU)

Remote ResourceControl Unit

(RRCU)Resource Control

Unit (RCU)Resource Control

Unit (RCU)

Client Side WOS NodeClient Side WOS Node Server Side WOS NodeServer Side WOS Node

Graphical UserInterface

Graphical UserInterface

Ware-houseWare-house

Ware-houseWare-house

WOS is a set of versioned nodes where each node offers a minimal set of services

P.G. Kropf, H. Unger and G. Babin. <<WOS: An InternetComputing Environment>>. PACT Workshop on UbiquitousComputing, Philadelphia, USA, October 2000.


TheThe Nature of WOSNature of WOSInfrastructure of WOSInfrastructure of WOS

WOSRPWOSP

WOSnode

WOSnode

WOSnode

Netw

orkN

etwork

Softw

areR

esourcesW

arehouse

Har

dwar

eR

esou

rces

War

ehou

seInformation Warehouse

Request Warehouse

Search Evaluation

API UI

Local O/S


TheThe Nature of WOSNature of WOSCommunicationCommunication FrameworkFramework

! The WOS Protocol (WOSP)– Simple generic syntax– Extensible– A version of WOSP is a specialization of the generic

syntax

! The WOS Request Protocol (WOSRP)– Search/Localization of WOS nodes– Exchange of information about WOSP version– Establishment of WOSP connections


TheThe Nature of WOSNature of WOSService classes of WOSService classes of WOS

! A WOS node provides a set of service classes– A service class is a set of services of same nature– Example : Configuring and executing High Performance (HP)

applications (e.g. on grids)– A user query is served by a specific service belonging to a

specific service class

! All service classes respect the generic WOS Protocol(WOSP)– Every service class has its own semantic– We define a specific version of WOSP for each service class– A service class is a WOSP version

! Services are dynamic and must be able to evolve


TheThe Nature of WOSNature of WOSInformationInformation FrameworkFramework

! Resource Warehouses– Contain the description of the local resources provided by the

WOS node– Preserve information about remote resources already requested

! What is resource ?– Hardware : CPU, Memory, etc.– Software : Java, PVM, MPI, WOSP version, etc.– Documents, data files– Others : Effective CPU or Network performance, etc.

! Warehouses are distributed and have limited storagecapacity– They learn and forget information


TheThe Nature of WOSNature of WOSInformationInformation FrameworkFramework

! A resource is describedby attributes: an attributeand its associated valueis called an av-pair

! The structure of awarehouse is ahierarchical arrangementof av-pairs: An av-pair is adescendent of another av-pair when it depends on it


UserUser RequestsRequests

! Users make requests to identify services that fulfilltheir needs

! Requests are built using arrangements ofattributes and values, linked by relationaloperators: av-relations– For example

• [Attribute:Price ≤≤≤≤ Value: 10 dollars]

! A request consists of two predicates– Pu : user-specific characteristics of the service– Pc : context-specific characteristics of the service


ProcessingProcessing a Usera User RequestRequest::TheThe SearchSearch AlgorithmAlgorithm

Search (Pu, Pc, q) : tries to return at least q services matching Puand Pc

1. Performs a local request : Request (Pu, Pc, q)– If the number of services found is sufficient, the algorithm stops

2. Performs a remote request– Finds nodes with the same context from local warehouses– Performs the request on each of these remote nodes– If the number of services found is sufficient, the algorithm stops

3. Performs a remote request (2nd try)– Finds any node from known remote nodes– Performs the request on each of these remote nodes– If the number of services found is sufficient, the algorithm stops

4. Find at least one other WOS node– Uses a Bootstrap algorithm– Restarts at step 1


PerformingPerforming a Locala Local RequestRequest::TheThe RequestRequest AlgorithmAlgorithm

Request (Pu, Pc, q) : tries to return at least q servicesmatching Pu and Pc from the local warehouses

– The best case• We find at least q services matching Pu and Pc

– The intermediate case• We gradually reduce the constraints imposed by Pc until we

find at least q services

– The worst case• We find all the services only matching Pu

• The set of services found may be empty


Notion of Best FitNotion of Best Fit

! Best Fit means the services which match the user requestand most or all of the contextual parameters

! Example– Pu = [Attribute: service = value: printing] (user-specific)

– Pc = [Attribute: building = value: HEC] (context-specific)

– The search algorithm will try to choose all printers located inthe HEC building

• [value: HEC]

– Otherwise, the search algorithm would provide the user withprinting services in other buildings


Managing WarehouseManaging Warehouse ContentContent

! WOS nodes have limited storage capacities– Warehouses cannot grow indefinitely– Mechanisms must be put in place to control the size of

warehouses

! Warehouses are updated whenever a WOS node receivesanswers from remote nodes– Decisions must be taken whether to insert, update, or remove

information.

! For each av-pair in a warehouse, we keep track of– Its creation date– Its last modification date– Its number of access

! This information enables a WOS node to properly managethe limited storage capacity allocated to it


TheThe Nature of WOSNature of WOSRelated WorkRelated Work

! The WOS may be distinguished by the decentralized natureof the search– JINI handles service lookup and discovery using a centralized

server– JXTA may use a completely decentralized, a completely

centralized, or a mixed approach– The Service Location Protocol (RFC 2608) proposes a service

lookup algorithm based on multicast– INS uses a decentralized network of resolvers to discover

names and route messages– DHT lookup methods use symmetric and structured approaches

(Chord, Pastry, CAN, etc.)

! The WOS also describes how services are named– JXTA and does not address how to name and bind services and

resources


Applications of WOSApplications of WOS

! Virtual communities– Shared contexts– Adaptive, dynamic

management of federations

! Grid computing– Transparent remote execution– Transparent distributed file

system access

! E-Commerce– Discovery of business

partners– Transparent transmission of

business data

! Information systems– Distributed document/data

sharing systems

any-time, any-where, any-service, any-mediumThe WOS for


Grid computing :Grid computing :HHigh Performanceigh Performance WOSWOS Protocol :Protocol : HHPP--WOSPWOSP

! HP-WOSP is a class of services used to configureHigh Performance applications

! Services of HP-WOSP are :– Discovery Service : HP-WOSP (discovery, pgm)– Reservation Service : HP-WOSP (reservation, pgm)– Setup Service : HP-WOSP (setup, pgm)

HP-WOSP

HP-WOSP

User Request

WOSRP RequestWOSRP Reply

X-WOSP RequestX-WOSP Reply

HP-WOSP


E-commerce busOpen Electronic Marketplace ArchitectureInternet Standards

Web (http,html,xml)electronic signatures

encryption, e-mail

Buyers’ serverMarket Portal

MarketplaceNegotiation serverMarket rules and

mechanisms

Sellers’ server

Productsand/orServices

Market DTDNormalization

XMLdictionaries

Product indexand search tools

Searchagents

Marketoversight

Advisors

E-commerce Infrastructure

Market Databases

Applications of WOSApplications of WOSEE--CommerceCommerce


Applications of WOSApplications of WOSEE--CommerceCommerce

! Functions of an open e-commerce bus– Search functions

• Potential business partners• Product/service catalogues

– Support functions• Accreditation and certification mechanisms• Secure data communication• Trust management mechanisms

! Dynamic nature of the e-commerce bus– Function set may evolve over time– Dynamic communities of participants– Context of operation changes– Manages diversity


OtherOther applicationsapplicationsWOSForwardWOSForward serviceservice


BeyondBeyond WOSWOS

! Nature of the Web/Internet– Dynamic, heterogeneous, global environment– Rapid development of distributed and mobile systems– Multitude of different applications and services

! The services offered have to evolve:– The most efficient hardware/software environment should

be provided and used– Services and environments have to adapt to their

contexts.

! Ubiquitous Computing Vision :– any-time, any-where, any-service, any-media, any-device


Ubiquitous ComputingUbiquitous Computing

! The disappearing computer: from fixed to mobile to wearable! It is about the Computer in the World and NOT the World in

the Computer : bridging the gap between virtual and realworld

! Context- and location-aware, diverse and numerous, human-centric

! Much technology driven: Moore’s law! Smart devices with spontaneous network capabilities that

have access to any information or provide access to anyservice “on the net”

! Vision: everyday objects become smart and interconnected;they communicate and cooperate : communities


Ubiquitous ComputingUbiquitous Computing


CommunityCommunity supportsupport

Virtual RoomsPortals Enterprise

Games Entertainment


Open environments - DistributedOpen environments - Distributedcommunitiescommunities

! The “any-” vision calls for concepts to structurethe diversity

! Open environment – components:– Autonomous– Heterogeneous– Numerous (large scale)– Mobile and adaptive in space and time– Context aware– Collaborative– Dynamic membership (join/change/leave)

! Decentralized – self-organized – adaptivelystructured

Distributed Communities


Distributed CommunitiesDistributed Communities

! Distributed communities : evolving associations ofparticipants (people, devices, software), mediatedby a shared context.

! Community : medium of collaborationtransforming the participants involved

! Not a space for random interaction betweenindividuals, but a structure for efficient interactionto acquire and disseminate information


Merci !

Universitéde Montréal

[email protected] www.iro.umontreal.ca/~kropf

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