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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
21 février 2003Université de Montréal 3
! 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
21 février 2003Université de Montréal 4
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
21 février 2003Université de Montréal 5
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
21 février 2003Université de Montréal 6
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.
21 février 2003Université de Montréal 7
RationaleRationale for WOSfor WOS
WOSMiddleware/Services
Self-configuring networks of mobile and stationarydevices form communities
21 février 2003Université de Montréal 8
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.
21 février 2003Université de Montréal 9
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
21 février 2003Université de Montréal 10
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
21 février 2003Université de Montréal 11
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
21 février 2003Université de Montréal 12
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
21 février 2003Université de Montréal 13
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
21 février 2003Université de Montréal 14
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
21 février 2003Université de Montréal 15
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
21 février 2003Université de Montréal 16
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
21 février 2003Université de Montréal 17
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
21 février 2003Université de Montréal 18
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
21 février 2003Université de Montréal 19
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
21 février 2003Université de Montréal 20
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
21 février 2003Université de Montréal 21
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
21 février 2003Université de Montréal 22
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
21 février 2003Université de Montréal 23
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
21 février 2003Université de Montréal 24
OtherOther applicationsapplicationsWOSForwardWOSForward serviceservice
21 février 2003Université de Montréal 25
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
21 février 2003Université de Montréal 26
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
21 février 2003Université de Montréal 27
Ubiquitous ComputingUbiquitous Computing
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CommunityCommunity supportsupport
Virtual RoomsPortals Enterprise
Games Entertainment
21 février 2003Université de Montréal 29
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
21 février 2003Université de Montréal 30
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
21 février 2003Université de Montréal 31
Merci !
Universitéde Montréal
[email protected] www.iro.umontreal.ca/~kropf