Software Composition 2009

1. Composing RESTful
Services with JOpera
Cesare Pautasso
Software Composition 2009
Zurich, Switzerland
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 1

2. Composing RESTful Services
with JOpera
Cesare Pautasso
Faculty of Informatics
University of Lugano (USI), Switzerland
http://www.pautasso.info
http://www.jopera.org
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 2

3. Web Service Composition Today
Composition Language WS-BPEL 2.0
Component Model WSDL 1.1
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]
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 3

4. RESTful Web Services APIs…
WSDL 1.1
…do not use
WSDL 1.1
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 4

5. Our Goal
 Compose RESTful Web Services into
Mashups
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 5

6. Web 2.0 Mashups
 Software Composition for the Web
A mashup is a web application that
combines data or functionality from
two or more external sources to
create a new service
[Wikipedia]
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 6

7. Example Mashup with RESTful Web Services
+ + =
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 7

8. Our Goal
 Compose RESTful Web Services into
Mashups
Our Current Solution: JOpera
 Workflow-based, Visual Composition Language
 Abstract and Extensible Component Model
 Eclipse-based Integrated Composition Environment
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 8

9. Agenda
 Motivation
 REST Introduction (one slide)
 Composing RESTful services
 Demo: Doodle Map Mashup with JOpera
 Challenges
 Discussion
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 9

10. REST in one slide PUT
 Web Services expose their
data and functionality trough GET
R
resources identified by URI POST
DELETE
 Uniform Interface: Clients interact
with the state of resources through 4 verbs:
GET (read), POST (create), PUT (update), DELETE
 Multiple representations for the same resource
 Hyperlinks model resource relationships, valid
state transitions and interaction protocols
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 10

11. REST design elements
 Resources are published by Origin Servers
 Proxy/Gateways for caching, access control, adaptation
HTTP
User Agent Origin Server
HTTP HTTP
User Agent Proxy/Gateway Origin Server
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 11

12. What about composition?
 The basic design elements of the REST architectural style do
not take composition into account
HTTP
User Agent Origin Server
Origin Server
User Agent
HTTP
Composite
? HTTP
Origin Server
RESTful service
Origin Server
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 12

13. Composite Resources
DELETE
PUT
GET
C
DELETE DELETE
POST PUT PUT
GET
R GET
S
POST POST
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 13

14. Doodle Map Mashup
 Setup a Doodle with Yahoo! Local search and
visualize the results of the poll on Google Maps
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 14

15. Doodle Map Composite Resources
Client Composite Component
Web Browser Resources Resources
M GET
Y
GET
PUT
POST
GET
P GET
D
POST
GET
G
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 15

16. Doodle Map Architecture
Web Browser JOpera RESTful
Engine Web Services
GET APIs
POST GET
POST
GET
RESTful API
RESTful API
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 16

17. Demo
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 17

18. Modeling the Composition in JOpera
Control Data
Flow Flow
Service
Bindings
JAVA XPATH XSLT HTML HTTP …
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 18

19. Control
Flow
Control Flow
Dependency
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 19

20. Data
Flow
Data Flow
(Copy)
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 20

21. Service
Bindings
HTTP
HTML
XSLT
XPATH
JAVA
…
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 21

22. Composition and REST: Some Challenges
 Resource addressing through URI
 How to interact with dynamic, variable set of URI?
 Uniform Interface (GET, POST, PUT, DELETE)
 Is this a new composition technique?
 Multiple resource representations
 Resource data type may only be known at run-time
 How to negotiate the most appropriate representation
format?
 Hyperlinks
 Can the state of a composition be bookmarked?
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 22

23. Resource Addressing through URI
 How to interact with dynamic, variable set of URI?
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 23

24. Uniform Interface (GET, POST, PUT, DELETE)
 Is this a new composition technique?
 Easy to configure the HTTP method in the adapter
 Hard to handle failure/idempotency semantics
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 24

25. Multiple Resource Representations
 Resource data type may only be known at run-time
 How to negotiate the most appropriate representation format?
Set HTTP Headers (Accept)
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 25

26. Hyperlinks
 Can the state of a composition be bookmarked?
Follow hyperlinks
Generate hyperlinks
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 26

27. Composition and REST: More Challenges
 Missing Interface Description
 How to compose services without machine readable
interface descriptions?
 Request correlation
 How to ensure stateless communication with the right
instance of a composition?
 Caching/Idempotency
 Verification and Testing
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 27

28. Conclusion
 Business Process Modeling Languages have been
applied with success to compose “traditional” WS-*
Web Services
 Business Process Modeling Languages should also be
applied to compose RESTful Web Services
 JOpera for Eclipse is a visual process modeling tool
with an extensible engine for composing both kinds of
services (and many more) into Web 2.0 mashups
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 28

29. Composing RESTful Services
with JOpera
Cesare Pautasso
Faculty of Informatics
University of Lugano (USI), Switzerland
http://www.pautasso.info
www.jopera.org
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 29

30. PhD positions available!
Prof. Cesare Pautasso
University of Lugano, Switzerland
c.pautasso@ieee.org
http://www.pautasso.info
2.7.2009 30
©2008 Cesare Pautasso

31. Mashups09 @ OOPSLA
http://www.mashup-oopsla.org/
3rd International Workshop on
Web APIs and Services Mashups
2 July 2009 ©2009 Cesare Pautasso | www.pautasso.info 31