Chapter 20: Social Service Selection

1. Chapter 20:Social Service Selection Service-Oriented Computing: Semantics, Processes, Agents– Munindar P. Singh and Michael N. Huhns, Wiley, 2005

2. Highlights of this Chapter • Reputation Mechanisms • Recommender Techniques • Referrals • Social Mechanism for Trust • Identity Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

3. Recommending Products vs. Services • Products (by a product vendor): often, • The recommender is the provider • Votes are known to the recommender • Votes are received prior to usage (buying) • Repetition is less likely (buy the same book?) • Services (by a service registry) • The recommender is not the provider • Votes are not necessarily known to recommender • Votes are given after usage • Repetition may occur, invisibly to registry Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

4. ReputationComputationally treated as centralized The agency (e.g., eBay) is the central authority that • Authenticates users • Records, aggregates, and reveals ratings • Provides the central conceptual schema for • How to capture ratings (e.g., numbers and text) • How to aggregate them • How to decay them over time Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

5. Service Communities • Each principal • Provides services to each others • Provides recommendations to others • Exploits services provided by others • Has a reputation • The agents assist their users and other agents in • Evaluating the services and referrals provided by others • Maintaining models of acquaintances • Deciding whom to contact for a service Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

6. Social Networks and Referral Chains • Referral chains in networks provide: • Way to identify a good provider • Way to judge the quality of a provider • Reason for a member to respond in a trustworthy manner • As the chains get longer • The trustworthiness of a recommendation decreases • The effort to find providers increases • Therefore, shorter chains are better • Technical challenge: how can we find such? Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

7. Distributed Treatment of Referrals Receive request Ask Model asker Follow referrals Respond Use Rate; update Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

8. Agent Model for Referrals Model each agent via its • Interest (services sought) • Expertise (services provided) • Models of its acquaintances representing their • Expertise (ability to provide good services) • Sociability (ability to provide accurate referrals) Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

9. Reputation Buildup and Collapse A participant who begins to misbehave is detected Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

10. Small World Phenomenon Milgram (1967): two individuals chosen at random in the U.S.A. are linked by a chain of 6 or fewer first-name acquaintances (empirical observation) • Six degrees of separation • Erdös numbers • Diameter of the connected Web: 20 Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

11. Small-World Network • Generated by perturbing a regular ring • A highly structured (clustered) network with just a few random edges • Random edges correspond to shortcuts • Yields high clustering and short paths • Direct relationships between agents who primarily belong to distinct subcommunities • Shortcuts: weak ties Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

12. Quality Relates Inversely to Clustering Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

13. Weak Ties versus Clustering • Conventional approaches recommend based on preferences of similar users • But, it is better to ask dissimilar people who bring a novel perspective • Define a form of controlled scattering Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

14. Link Analysis • Web link: recommendation by page author • An external criterion for estimating the value of a page to others • Typically, web engines crawl the web, build giant indexes, and analyze links • Referral: dynamic, targeted recommendation by an agent • Similar mathematical concepts to above apply Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

15. Chapter 20 Summary • Selection should be empirical: based on data • Centralized reputation mechanisms gather data but impose many restrictions • Research Challenges • Social networks can avoid the above limitations • Referrals help maintain distributed social networks • Social structure can evolve collaboratively • Services can be rated and selected and rated again, and so on … Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns