Combining Service–Oriented Computing & Peer-to-Peer Computing

1. Combining Service–Oriented Computing & Peer-to-Peer Computing A Position Paper By: Aleksandr Morozyuk Andreas Loizias Nihir Patel Sumant Luthra

2. Introduction • Over a number of years, business applications have been built to satisfy particular requirements • Integration of business applications was based on loose and awkward interfaces which produced poor results: • Redundancy of Code • Increase of Errors • Costs of Development

3. Introduction (cont’d) • Service-Oriented Architecture (SOA) was adopted to overcome the issues of the traditional approach by integrating existing and new services • Two types of integration of services: • Service-oriented computing: • Based on a centralized UDDI registry • Peer-to-peer computing: • Based on peer-to-peer networks

4. Introduction (cont’d) • Our position is that there is a need to combine the centralized and peer-to-peer computing approaches in order to improve service-oriented computing.

5. Problems with Centralized Architecture • Three major participants: • Service Provider • Service Broker • Service Consumer

6. Problems with Centralized Architecture (cont’d) • The centralized UDDI model suffers from the usual problems that centralized computing systems do: • Performance bottleneck • Single point of failure • Vulnerable to Denial of Service Attacks • Increase of response times • Possible Solutions: • Add more servers • Use load-balancing techniques • However, these solutions have proven to be expensive and troublesome!

7. P2P as a better solution • P2P architecture is a better solution than the centralized UDDI model • P2P network is a collection of independent nodes representing web services

8. P2P as a better solution (cont’d) • P2P approach provides the following advantages: • Dynamic discovery • Complete decentralization • Availability and Reliability • Fault-tolerance • No bottlenecks • Quick response time on updates • Three approaches to combine P2P and centralized: • Federation • Ontology-based • Based on Keywords and Indexing

9. Federation Approach • The Federation approach allows us to fuse web services with P2P networks in a decentralized fashion • Federation is a group of peers with common interests • Major key entities: • Specialized UDDI • Syndication of Peers • Super Peer • Local UDDI • Service Peers • Each service peer registers its web services either locally (syndication UDDI) or centrally (specialized UDDI) • Super peer takes responsibility of handling publications and subscriptions locally

10. Federation Approach • Formation of Syndication: • New peer submits its publication to specialized UDDI • New peer may join a service syndication • A copy of the new peer’s publication is sent to the syndication UDDI • Two key concepts of peer syndication: • Publication: name, description, ports and bindings of a web service • Subscription: name, description and service requirements of requesters • Super peer responsibilities: • Receive and store publications and subscriptions for the entire syndication • Match publications with subscriptions to route and deliver notifications • Keep potential subscribers informed of new registrations and deletions

11. Federation Approach • Matching Process: • Match new peer’s publication against relevant subscriptions • Match new peer’s subscription against existing publications: • New peer receives information about peers whose publications match its subscriptions • Each peer knows the identity of the peers in its own syndication that match its own subscriptions • Peers can form their own peer-acquaintance groups (PAG) and work autonomously without interacting with their super-peer • Federations consist of several super-peers used for notification services and other peers within the syndication form their own peer groups

12. Conclusion Centralized UDDI model is inherent to certain problems: • Availability issues: • Exponential growth of the registry • Malicious attacks • Software failure • Hardware failure • Peer-to-Peer publication and discovery scheme can solve the problems posed by the Centralized UDDI model • Can fully utilize the power and flexibility of a completely distributed platform

13. Single Point of Failure?

14. Problems with the P2P model • High Bandwidth consumption • Connections to peers are not secure • Complexity makes implementation and maintenance difficult • Has to send queries to every peer on the network • The super-peer/syndications model though eliminates the need to send the queries to every peer since queries are matched with publications by the super-peer. • The Federated model can be made secure by introducing encryption

15. Our Position We Acknowledge the Problems of the Peer-to-Peer model We believe that despite the problems, the “Federated Architecture” model would still greatly benefit web services, eliminate most of the problems of the centralized registry architecture and make better use of the distributed and loosely connected nature of web services

16. References • Papazoglou, Mike P., Bernd J. Kramer, and Jian Yang, “Leveraging Web- Services and Peer-to-Peer Networks”, Lecture Notes in Computer Science, 2681:485-501, Springer-Verlag GmbH, 2003 • Samtani, Gunjan and Dimple Sadhwani "Web Services and Peer-to-Peer Computing" Companion Technologies http://www.webservicesarchitect.com/content/articles/samtani05.asp • Malladi, Venkata Sastry “Integrating Web Services and P2P” Columbia University http://www1.cs.columbia.edu/~vsm2101/courses/6125/wsp2p.pdf • Schmidt, Cristina, Manish Parashar, “Flexible information discovery in decentralized distributed systems”, High Performance Distributed Computing, 2003 Proceeding: 226-235, 12th IEEE International Symposium, 2003 • Paolucci, Massimo, Katia Sycara, Takuya Nishimura, Naveen Srinivasan “Using DAML-S for P2P Discovery” http://www.cs.cmu.edu/~softagents/papers/p2p_icws.pdf • Whitten, Jeffery L., Lonnie D. Bentley, Kevin C. Dittman, “Systems Analysis and Design Methods”, McGraw-Hill/Irwin, New York, 2004 • Govoni, Darren “Web Services Over P2P Networks” http://webservices.sys-con.com/read/39425.htm