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. Reputation The agency (e.g., eBay) is the authority that • Authenticates users • Records, aggregates, and reveals ratings • Provides the conceptual schema for • How to capture ratings (typically a number 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 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 contact lists • 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 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 Social networks induce referral chains in which an individual may participate • As the chains get longer • The trustworthiness of a recommendation decreases • The effort to find providers increases • Therefore, shorter chains are better 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. Model for Referrals • Each agent has • An interest (services sought) • An expertise (services provided) • Models of acquaintances • Acquaintance models are built autonomously and represent • Acquaintances’ expertise (ability to provide good service along a set of dimensions) • 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 participate in different 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 give recommendations based on the preferences of similar users (as discussed previously) • For finding the best referrals, it is best 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 • Links on a web page correspond to recommendations by the page author • Links provide an external criterion for estimating the value of a page (as opposed to words on a page, which can be rigged) • Typically, web engines crawl the web, build giant indexes, and analyze links • A referral corresponds to a targeted recommendation by an agent. While we may not crawl referrals ahead of time, the same mathematical concepts apply Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns

15. Chapter 20 Summary • Selection must rationally be empirical: based on data • Centralized reputation mechanisms address data gathering but impose too many restrictions • Social network ideas can avoid such limitations • Referrals help maintain distributed social networks and incorporate purposes • Social structure can evolve collaboratively • Services can be rated and selected and rated … Service-Oriented Computing: Semantics, Processes, Agents - Munindar Singh and Michael Huhns