1. Middleware & Web Services

2. Layered Protocols: IP Layers, interfaces, and protocols in the Internet model.

3. Purpose of Layered Models  mask the heterogeneity of systems  provide convenient programming abstraction

4. Layered Protocols: OSI TvS 2.2 Layers, interfaces, and protocols in the OSI model.

5. Middleware Protocols An adapted reference model for networked communication. TvS 2.6

6. Purpose of Middleware  ‘Middleware is primarily a set of programming abstractions developed to facilitate the development of complex distributed systems.’ – Gustavo Alonso 

7. Middleware provides…  protocols to support general-purpose services to more specific applications, e.g.  authentication protocols  authorization protocols  distributed commit protocols  distributed locking protocols  high-level communication protocols ^remote procedure calls (RPC) ^remote method invocation (RMI)

8. Middleware 1-22 TvS 1.24 General structure of a distributed system as middleware.

9. Middleware and Openness In an open middleware-based distributed system, the protocols used by each middleware layer should be the same, as well as the interfaces they offer to applications. 1.23 TvS 1.25

10. Old-style Middleware programming models  Remote Calls  Remote Procedure Calls (RPC)  Distributed objects and Remote Method Invocation  E.g. Java RMI  Common Object Request Broker Architecture (CORBA)  Cross-language RMI  Other Programming Models  Remote event notification  Remote SQL access  Distributed transaction processing

11. ©Gustavo Alonso, ETH Zürich. WS architecture: application integration o A popular interpretation of Web services is based on IBM’s Web service architecture which is based on three elements: ÞService requester: The potential user of a service ÞService provider: The entity that implements the service and offers to carry it out on behalf of the requester ÞService registry: A place where available services are listed and which allows providers to advertise their services and requesters to query for services o The goal is just-in-time integration of applications by discovering and orchestrating network-available services

12. ©Gustavo Alonso, ETH Zürich. How is it ‘bottom up’? o The Web service architecture proposed by IBM is based on two key concepts: Þarchitecture of existing synchronous middleware platforms Þcurrent specifications of SOAP, UDDI and WSDL o The architecture has a remarkable client/server flavor o It reflects only what can be done with ÞSOAP (Simple Object Access Protocol) ÞUDDI (Universal Description and Discovery Protocol) ÞWSDL (Web Services Description Language) UDDI SOAP WSDL

13. Message-based Middleware  Asynchronous  Sending and receiving documents  No remote procedure calls or object invocation  Less coordination required

14. ©Gustavo Alonso, ETH Zürich. The message world

15. Sources: Middleware  Adapted from Introduction to Distributed Systems: Slides for CSCI 3171 Lectures by E. W. Grundke  References: [TvS] A. Tanenbaum and M. van Steen Distributed Systems: Principles and Paradigms, Prentice-Hall (2002) http://www.prenhall.com/divisions/esm/app/author_tanenbaum/custom/dist_sys_1e/ [CDK] G. Coulouris, J. Dollimore and T. Kindberg  Distributed System: Concepts and Design, Addison-Wesley (2001)  http://www.cdk3.net/ig/beida/ [ISO] International Organization for Standardization/ International Electrotechnical Commission Standard ISO/IEC 7498-1: Information Technology — Open Systems Interconnection — Basic Reference Model: The Basic Model (Second ed., corrected and reprinted 1996-06-15) Reference number ISO/IEC 7498-1:1994(E)  http://standards.iso.org/ittf/PubliclyAvailableStandards/s020269_ISO_IEC_7498- 1_1994(E).zip

16. Sources: Web Services  Gustavo Alonso, Fabio Casati, and Harumi Kuno. Web Services: Concepts Architectures and Applications (Springer-Verlag, 2004) Slides from.http://www.inf.ethz.ch/~alonso/WebServicesBook  Gustavo Alonso and Cesare Pautasso. Graduate course given at the University of Lappeenranta,Finland. August 9–13, 2004. http://www.inf.ethz.ch/personal/alonso/Web-book/Lappeenranta-graduate-course.zip