Centralization vs. Decentralization Issues in Internet-based .ppt

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1、July 13, 2000,TWIST 2000,Centralization vs. Decentralization Issues in Internet-based KMS: Experiences from Expertise Recommender Systems,Dawit Yimam, GMD-FIT.MMK& Alfred Kobsa, UCI, ICS,July 13, 2000,TWIST 2000,Outline,Background First centralized approach Alternatives - to centralize or decentrali

2、ze ? DEMOIR Summary,July 13, 2000,TWIST 2000,Expert Recommenders/Finders,Systems to help users in tracing human information and/or expertise sources in organizations part of knowledge management and knowledge sharing services. Traditionally done by manual construction and search of expertise descrip

3、tions of people, e.g., Expert Databases (“knowledge directories”) Personal web pages on the Web Automatically mining implicit sources of expertise evidence from electronic resources of an organization and its people.,Background,Alternatives,First appr.,DEMOIR,Summary,July 13, 2000,TWIST 2000,Charact

4、erizing Expert Finders,1. Expertise evidence/indicator source recognition and gathering 2. Expertise modeling- Expertise indicator extraction- expertise model representation 3. Expertise model deployment- query mechanisms- matching operation- output delivery/presentations- adaptation and learning op

5、erations,Background,Alternatives,DEMOIR,Summary,First appr.,July 13, 2000,TWIST 2000,Query-time expertise modeling,Web Site Indexing,Web Documents Index,Background,Alternatives,DEMOIR,Summary,Glimpse,FIT Peoples and other Web Pages,WebGlimpse,First appr.,July 13, 2000,TWIST 2000,Query-time expertise

6、 modeling,Query (Boolean),Background,Alternatives,DEMOIR,Summary,Web Site Indexing,Web Documents Index,Glimpse,FIT Peoples and other Web Pages,WebGlimpse,Expert Query Interface,First appr.,July 13, 2000,TWIST 2000,Query-time expertise modeling,Expert Database (Name, URL),Search,Ranked List of Expert

7、s,Background,Alternatives,DEMOIR,Query (Boolean),Web Site Indexing,Web Documents Index,Glimpse,FIT Peoples and other Web Pages,WebGlimpse,Expert Query Interface,Search Result (passages containing Keywords),Expertise Modeler & Tracer,First appr.,Summary,July 13, 2000,TWIST 2000,Query-time expertise m

8、odeling,Shortcomings:high latency in query processing personal sources hard to include non-document sources (e.g. recommendation from people, social relations, etc.) hard to include full reliance on availability of some search engine limited exploitation of info due to lack of persistent expertise m

9、odels,Background,Alternatives,DEMOIR,First appr.,Summary,July 13, 2000,TWIST 2000,Building apps on text Indexes,Existing Web indexing systems use centralized indexes of distributed resources/collections. Distributed Indexing needed to cope with ever growing information on Internet. But, currently ce

10、ntralized global indexes (though may be distributed in a tightly coupled manner) consistently outperform decentralized indexing and query approaches. This favors centralizing the applications to be built on them.,Background,Alternatives,DEMOIR,First appr.,Summary,July 13, 2000,TWIST 2000,Pre-generat

11、ion of Expertise Models,Alternative 1: Personal expert finding agents Decentralized multi-agent system. Expertise modeling as well as searching done by self-managing personal agents residing in experts computers (e.g. Vivacqua, 1999; Foner, 1997).Alternative 2: Aggregated expertise modeling Based on

12、 centralized expertise models (that are either dynamically aggregated or linked to a pre-constructed ontology) (e.g. simple versions in Kautz Krulwich & Burkey, 1996). Can be distributed among tightly coupled cluster of machines.,Background,Alternatives,DEMOIR,First appr.,Summary,July 13, 2000,TWIST

13、 2000,Personal expert finding agents,Agent communication,Agent1 - ModelExpertise FindExpert,Personal Expertise Model,Agent2 - ModelExpertise FindExpert,Personal Expertise Model,Agentn - ModelExpertise FindExpert,Personal Expertise Model,Agent3 - ModelExpertise FindExpert,Personal Expertise Model,Bac

14、kground,Alternatives,DEMOIR,First appr.,Summary,July 13, 2000,TWIST 2000,Aggregated Expertise Modeling,Expert Finding Server,Aggregated Expertise Model,Background,Alternatives,DEMOIR,First appr.,Summary,July 13, 2000,TWIST 2000,Aggregated Expertise Modeling,Expert Finding Server,Aggregated Expertise

15、 Model,Gateway (broker),local Expertise Model,Server1,local Expertise Model,Server1,local Expertise Model,Servern,L A N,Background,Alternatives,DEMOIR,First appr.,Summary,July 13, 2000,TWIST 2000,Aggregated Expertise Modeling,Expert Finding Server,Aggregated Expertise Model,Gateway (broker),local Ex

16、pertise Model,Server1,local Expertise Model,Server1,local Expertise Model,Servern,Gateway (broker),Server1,Server1,Servern,Central Expertise Model,L A N,L A N,Background,Alternatives,DEMOIR,First appr.,Summary,July 13, 2000,TWIST 2000,Analysis,Background,Alternatives,DEMOIR,First appr.,Summary,July

17、13, 2000,TWIST 2000,Analysis (contd.),Background,Alternatives,DEMOIR,First appr.,Summary,July 13, 2000,TWIST 2000,Hybrid Approach,Combine distributed agents with centralized expertise model server - “local-central” approachHow ? 1. Decentralized + centralized Expertise modeling Lightweight personal

18、agents for personal sources Configurable gatherers for organizational resources 2. Centralized (but “distributable”) expertise information server 3. Decentralized Exploitation of expertise information (through clients),Background,Alternatives,DEMOIR,First appr.,Summary,July 13, 2000,TWIST 2000,DEMOI

19、R - A Hybrid Architecture,Organizational Information Resources,Expertise- indicator Source Gatherers,Source Type Identifier,Source Wrapper2,Source Wrapper1,Source Wrappern,.,EISM,Ontology, Organizational structure, etc.,Aggregated Expertise Model,Expert Models,Remote Expert Details,API,Clients,Fuser

20、s,Expertise Information Space,Background,Alternatives,DEMOIR,First appr.,Summary,July 13, 2000,TWIST 2000,DEMOIR - A Hybrid Architecture,Gathering (decentralized Centralized),Modeling (decentralized/centralized),Exploitation (decentralized),Background,Alternatives,DEMOIR,First appr.,Organizational I

21、nformation Resources,Expertise- indicator Source Gatherers,Source Type Identifier,Source Wrapper2,Source Wrapper1,Source Wrappern,.,EISM,Ontology, Organizational structure, etc.,Aggregated Expertise Model,Expert Models,Remote Expert Details,API,Clients,Fusers,Expertise Information Space,Summary,July

22、 13, 2000,TWIST 2000,Summary/Observation,Centralized and decentralized options have their advantages and disadvantages. Many problem domains involve both “centralizable” and “decentralizable” tasksChallenges: isolating such tasks and identifying the tradeoffs b/n centralizing and decentralizing thei

23、r operations If both approaches are used, how to get them work together,Background,Alternatives,DEMOIR,Summary,First appr.,July 13, 2000,TWIST 2000,Summary/Observation,Centralization/decentralization is only one dimension of a systems architecture. Relate to: size/complexity of system (e.g. number o

24、f different parts, dynamism of their interaction, etc.) heterogeneity of data and their sources accessibility (e.g. permissions/privacy constraints, manner of use) communication patterns among componentskeep these in mind and analyze how they affect centralization/decentralization decision.,Backgrou

25、nd,Alternatives,DEMOIR,Summary,First appr.,July 13, 2000,TWIST 2000,Summary/Observation,What we did (in retrospect):1. Identify system requirements/tasks2. Identify and analyze centralized and decentralized alternatives of performing identified tasksthereby identify and evaluate general centralizati

26、on and decentralization factors in the problem domain.3. Specify optimum system components as well as architecture (i.e. trying to achieve advantages and avoid disadvantages of alternatives)aim at flexibility to allow varying degrees of centralization and/or decentralization to suit different deployment environments.,Background,Alternatives,DEMOIR,Summary,First appr.,