1. Yimam & Kobsa July 13, 2000TWIST 2000 Centralization vs. Decentralization Issues in Internet-based KMS: Experiences from Expertise Recommender Systems Dawit Yimam, GMD-FIT.MMK & Alfred Kobsa, UCI, ICS

2. Yimam & Kobsa July 13, 2000TWIST 2000 Outline Background First centralized approach Alternatives - to centralize or decentralize ? DEMOIR Summary

3. Yimam & Kobsa July 13, 2000TWIST 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 descriptions 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

4. Yimam & Kobsa July 13, 2000TWIST 2000 Characterizing 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 operations Background Alternatives DEMOIR Summary First appr.

5. Yimam & Kobsa July 13, 2000TWIST 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.

6. Yimam & Kobsa July 13, 2000TWIST 2000 Query-time expertise 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.

7. Yimam & Kobsa July 13, 2000TWIST 2000 Query-time expertise modeling Expert Database (Name, URL) Search Ranked List of Experts 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

8. Yimam & Kobsa July 13, 2000TWIST 2000 Query-time expertise modeling 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 models Background Alternatives DEMOIR First appr. Summary

9. Yimam & Kobsa July 13, 2000TWIST 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 centralized 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

10. Yimam & Kobsa July 13, 2000TWIST 2000 Pre-generation 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 centralized expertise models (that are either dynamically aggregated or linked to a pre-constructed ontology) (e.g. simple versions in Kautz & Selman, 1998; Krulwich & Burkey, 1996). +Can be distributed among tightly coupled cluster of machines. Background Alternatives DEMOIR First appr. Summary

11. Yimam & Kobsa July 13, 2000TWIST 2000 Personal expert finding agents Agent communication Agent 1 ----------------- ModelExpertise FindExpert Personal Expertise Model Agent 2 ----------------- ModelExpertise FindExpert Personal Expertise Model Agent n ----------------- ModelExpertise FindExpert Personal Expertise Model Agent 3 ----------------- ModelExpertise FindExpert Personal Expertise Model Background Alternatives DEMOIR First appr. Summary

12. Yimam & Kobsa July 13, 2000TWIST 2000 Aggregated Expertise Modeling Expert Finding Server Aggregated Expertise Model Background Alternatives DEMOIR First appr. Summary

13. Yimam & Kobsa July 13, 2000TWIST 2000 Aggregated Expertise Modeling Expert Finding Server Aggregated Expertise Model Gateway (broker) local Expertise Model Server 1 local Expertise Model Server 1 local Expertise Model Server n LANLAN Background Alternatives DEMOIR First appr. Summary

14. Yimam & Kobsa July 13, 2000TWIST 2000 Aggregated Expertise Modeling Expert Finding Server Aggregated Expertise Model Gateway (broker) local Expertise Model Server 1 local Expertise Model Server 1 local Expertise Model Server n Gateway (broker) Server 1 Server n Central Expertise Model LANLAN LANLAN Background Alternatives DEMOIR First appr. Summary

15. Yimam & Kobsa July 13, 2000TWIST 2000 Analysis Background Alternatives DEMOIR First appr. Summary

16. Yimam & Kobsa July 13, 2000TWIST 2000 Analysis (contd.) Background Alternatives DEMOIR First appr. Summary

17. Yimam & Kobsa July 13, 2000TWIST 2000 Hybrid Approach Combine distributed agents with centralized expertise model server - “local-central” approach How ? 1. Decentralized + centralized Expertise modeling Lightweight personal 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

18. Yimam & Kobsa July 13, 2000TWIST 2000 DEMOIR - A Hybrid Architecture Organizational Information Resources Expertise- indicator Source Gatherers Source Type Identifier Source Wrapper 2 Source Wrapper 1 Source Wrapper n... EISM Ontology, Organizational structure, etc. Aggregated Expertise Model Expert Models Remote Expert Details API Clients Fusers Expertise Information Space Background Alternatives DEMOIR First appr. Summary

19. Yimam & Kobsa July 13, 2000TWIST 2000 DEMOIR - A Hybrid Architecture Gathering (decentralize d Centralized) Modeling (decentralized/centralized) Exploitation (decentralized ) Background Alternatives DEMOIR First appr. Organizational Information Resources Expertise- indicator Source Gatherers Source Type Identifier Source Wrapper 2 Source Wrapper 1 Source Wrapper n... EISM Ontology, Organizational structure, etc. Aggregated Expertise Model Expert Models Remote Expert Details API Clients Fusers Expertise Information Space Summary

20. Yimam & Kobsa July 13, 2000TWIST 2000 Summary/Observation Centralized and decentralized options have their advantages and disadvantages. Many problem domains involve both “centralizable” and “decentralizable” tasks  Challenges: +isolating such tasks and identifying the tradeoffs b/n centralizing and decentralizing their operations +If both approaches are used, how to get them work together Background Alternatives DEMOIR Summary First appr.

21. Yimam & Kobsa July 13, 2000TWIST 2000 Summary/Observation Centralization/decentralization is only one dimension of a system’s architecture. Relate to: +size/complexity of system (e.g. number of 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 components  keep these in mind and analyze how they affect centralization/decentralization decision. Background Alternatives DEMOIR Summary First appr.

22. Yimam & Kobsa July 13, 2000TWIST 2000 Summary/Observation What we did (in retrospect): 1. Identify system requirements/tasks 2. Identify and analyze centralized and decentralized alternatives of performing identified tasks  thereby identify and evaluate general centralization 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.