Recent technology trends in Web services indicate that a solution eliminating the perceived complexity of the WS-* standard technology stack may be in sight: advocates of REpresentational State Transfer (REST) have come to believe that their ideas explaining why the World Wide Web works are just as applicable to solve enterprise application integration problems and to radically simplify the plumbing required to build service-oriented architectures. In this talk we take a very detailed look at the WS-* vs. REST debate by presenting a technical comparison based on architectural principles and decisions. We show how the two approaches differ in the number of architectural decisions that must be made and in the number of available design alternatives each provides. We will also reveal the truth behind the *perceived* complexity differences between these two architectural styles and we will demonstrate that there are very real consequences of choosing one over the other, resulting in both development and maintenance impacts. Our comparison helps technical decision makers to assess these two technology frameworks objectively and to select the one that best fits their needs.

1. REST vs. SOAP: Making the Right Architectural Decision Cesare Pautasso Faculty of Informatics University of Lugano (USI), Switzerland http:// www.pautasso.info

3. Web Sites (1992) HTTP HTML Web Browser Web Server

4. Web Sites (1992) HTTP HTML Web Browser Web Server (HTTP) SOAP Server Client XML WSDL WS-* Web Services (2000)

5. RESTful Web Services (2006) Client HTTP PO-XML RSS JSON Web Server WADL WS-* Web Services (2000) (HTTP) SOAP Server Client XML WSDL

7. XML URI HTTP MIME JSON RESTful SSL RSS

8. Is REST being used? Slide from Paul Downey, BT

9. Can we really compare WS-* vs. REST? WS-* REST

10. Can we really compare WS-* vs. REST? WS-* SOA Middleware Interoperability Standards REST Architectural style for the Web

11. How to compare? WS-* SOA Middleware Interoperability Standards REST Architectural style for the Web

12. How to compare? WS-* SOA Middleware Interoperability Standards REST Architectural style for the Web Architectural Decision Modeling

14. Application Integration Styles File Transfer Shared Database Message Bus Remote Procedure Call

15. Application Integration Styles File Transfer Shared Database Message Bus Remote Procedure Call WS-* REST Integration Technology Platform

16. Related Decisions (WS-*) File Transfer Shared Database Message Bus Remote Procedure Call WS-* REST

17. Related Decisions (RPC) File Transfer Shared Database Message Bus Remote Procedure Call WS-* REST

18. Decision Space Overview

22. RESTful Web Service Example HTTP Client (Web Browser) Web Server Database GET /book?ISBN=222 SELECT * FROM books WHERE isbn=222 POST /order INSERT INTO orders 301 Location: /order/612 PUT /order/612 UPDATE orders WHERE id=612

23. Big Web Service Example (from REST perspective) HTTP Client (Stub Object) Web Server POST /soap/endpoint POST /soap/endpoint return new Order() order.setCustomer(x) Web Service Implementation POST /soap/endpoint return getBook(222)

27. Conceptual Comparison

28. Conceptual Comparison

29. Conceptual Comparison

30. Technology Comparison

31. Technology Comparison

32. Technology Comparison

33. Technology Comparison

34. Technology Comparison

36. Measuring Complexity Decisions with 1 or more alternative options Decisions with more than 1 alternative options 35 27 Alternatives 14 17 Decisions WS-* REST 32 16 Alternatives 12 5 Decisions WS-* REST

38. Measuring Complexity Decisions with more than 1 alternative options Decisions with only 1 alternative option 32 16 Alternatives 12 5 Decisions WS-* REST 2 12 Decisions WS-* REST

40. Measuring Effort Decisions with only 1 alternative option Decisions with only do-it-yourself alternatives 2 12 Decisions WS-* REST 0 5 Do-it-yourself Alternatives WS-* REST

42. Freedom of Choice Freedom from Choice