![The WS-BPEL process model is layered on top of the service model defined by WSDL 1.1. […] Both the process and its partners are exposed as WSDL services [BPEL 2.0 Standard, Section 3] Web Service Composition Today “ ” WSDL 1.1 WS-BPEL 2.0](https://image.slidesharecdn.com/dagstuhlslideshare-1232563071102785-1/85/Composing-REST-Services-2-320.jpg)
Composing REST Services
- 1. Composing REST Services Open Dagstuhl Session Cesare Pautasso Faculty of Informatics University of Lugano (USI), Switzerland http:// www.pautasso.info
- 2. The WS-BPEL process model is layered on top of the service model defined by WSDL 1.1. […] Both the process and its partners are exposed as WSDL services [BPEL 2.0 Standard, Section 3] Web Service Composition Today “ ” WSDL 1.1 WS-BPEL 2.0
- 3. RESTful Web Services APIs… WSDL 1.1 … do not use WSDL 1.1
- 4. Compose RESTful Web Services Compose WSDL Web Services Use Business Process Modeling Languages The Goal Extend BPEL to support RESTful Web Services One Solution: BPEL for REST
- 5. Compose RESTful Web Services Compose WSDL Web Services Use Business Process Modeling Languages The Goal Visual Flow Language with Abstract Service Model Extensible Autonomic Engine Architecture Another Solution: JOpera
- 6. Web Services expose their data and functionality trough resources identified by URI Uniform Interface Principle: Clients interact with the state of resources through 4 verbs: GET (read), POST (create), PUT (update/create), DELETE Multiple representations for the same resource Hyperlinks model resource relationships and valid state transitions REST in one slide R PUT DELETE GET POST
- 7. Resource addressing through URI How to interact with dynamic, variable set of URI? Uniform Interface (GET, POST, PUT, DELETE) Does it help to make the verbs explicit in the workflow? Multiple resource representations How to negotiate the most appropriate representation? Hyperlinks Can the workflow implement state transition logic of a resource and generate new URIs dynamically as processes run to guide the clients invoking them? Challenges for Composition Languages
- 8. JOpera Example: Doodle Map Mashup Setup a Doodle with Yahoo! Local search and visualize the results of the poll on Google Maps
- 9. Doodle Map Mashup Architecture Web Browser Workflow Engine RESTful Web Services APIs GET POST GET RESTful API
- 11. BPM Workflow Languages RESTful Web Service Composition
- 12. Abstract Workflow Service invocation technology does not matter Concrete Workflow Expose service invocation technologies as explicit constructs in the workflow language RESTful Workflow Workflow as one kind of resource exposed by a RESTful service Solution Space BPM Workflow Languages RESTful Web Service Composition BPM Workflow Languages RESTful Web Service Composition BPM Workflow Languages RESTful Web Service Composition
- 13. WSDL 2.0 HTTP Binding can wrap RESTful Web Services 1. Abstract Workflow Example: BPEL/WSDL (WS-BPEL 2.0 does not support WSDL 2.0) R PUT R GET R POST R DELETE
- 14. Idea: Make REST interaction primitives first-class language constructs 2. Concrete Workflow: BPEL for REST <Put R> <Get R> <Post R> <Delete R>
- 15. BPEL for REST – New Activities/Handlers Web Service <invoke> Web Service <invoke> <receive> <reply> <receive> <put> <get> <post> <delete> <onPut> <onGet> <onPost> <onDelete> R esource PUT DELETE GET POST
- 16. Dynamically publish resources from BPEL processes and handle client requests BPEL for REST – Resource Block BPEL for REST < Resource P > <onGet> < Put R > < Get S > </onGet> < Post R > < Delete S > </onDelete> </Resource> <onDelete> R PUT DELETE GET POST S PUT DELETE GET POST P PUT DELETE GET POST
- 17. 3. RESTful Workflows P Use the resource interface abstraction to publish the state of the workflow
- 18. Publish workflows as resources identified by the URIs: /package/process /package/process/version /package/process/version/instance /package/process/version/instance/task /package/process/version/instance/task/parameter Workflows as Resources – URI
- 19. GET /package/process Enumerate deployed process versions GET /package/process/version Enumerate active instances of a given process version GET /package/process/version/instance Read the current state of a workflow instance GET /package/process/version/instance/task Read the current state of a workflow instance task GET /package/process/version/instance/task/param Read the current value of a workflow instance parameter Reading the state of the workflow resources
- 20. POST /package Deploy new process template into package POST /package/process Deploy new version of a process POST /package/process/version Create new process instance Creating new workflow resources
- 21. PUT /package/process/version/instance/task Update the state of a workflow task (e.g., finished, failed) PUT /package/process/version/instance/task/param Write into task parameters some values Updating the workflow resource
- 22. DELETE /package/process Undeploy all versions of a process (and all the corresponding process instances) DELETE /package/process/version Undeploy a version of a process (and all of its instances) DELETE /package/process/version/instance Remove the state of a specific process instance only Deleting workflow resources
- 23. Why should a workflow engine care about REST? Use workflows to compose RESTful Web services Implement RESTful services with a workflow Should a process explicitly include RESTful activities? Or it is better/enough to model REST implicitly? How much of the state of a process instance should be exposed as a resource? How to control which “parts” are visible? Discussion
- 24. Business Process Modeling Languages have been applied with success to compose “traditional” WS-* Web Services (BPM = SOA + BPEL) Business Process Modeling Languages should also be applied to compose RESTful Web Services BPEL for REST is a lightweight BPEL extension for REST and WS-* service composition JOpera for Eclipse is a visual process modeling tool with an extensible engine for composing both kinds of services (and many more) Conclusion
- 25. R. Fielding, Architectural Styles and the Design of Network- Based Software Architectures , PhD Thesis, University of California, Irvine, 2000 C. Pautasso, O. Zimmermann, F. Leymann, RESTful Web Services vs. Big Web Services: Making the Right Architectural Decision , Proc. of the 17th International World Wide Web Conference ( WWW2008 ), Bejing, China, April 2008 C. Pautasso, BPEL for REST , Proc. of the 7 th International Conference on Business Process Management (BPM 2008), Milano, Italy, September 2008 Xiwei (Sherry) Xu, Liming Zhu, Yan Liu, Mark Staples, Resource-Oriented Architecture for Business Processes , APSEC’08 Some References http://www.jopera.org/