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

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

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]
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RESTful Web Services APIs…
WSDL 1.1
…do not use
WSDL 1.1
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Our Goal
 Compose RESTful Web Services into
Mashups
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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]
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Example Mashup with RESTful Web Services
+ + =
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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

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

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
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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
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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
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Composite Resources
DELETE
PUT
GET
C
DELETE DELETE
POST PUT PUT
GET
R GET
S
POST POST
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Doodle Map Mashup
 Setup a Doodle with Yahoo! Local search and
visualize the results of the poll on Google Maps
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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

Doodle Map Architecture
Web Browser JOpera RESTful
Engine Web Services
GET APIs
POST GET
POST
GET
RESTful API
RESTful API
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Demo
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Modeling the Composition in JOpera
Control Data
Flow Flow
Service
Bindings
JAVA XPATH XSLT HTML HTTP …
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Control
Flow
Control Flow
Dependency
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Data
Flow
Data Flow
(Copy)
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Service
Bindings
HTTP
HTML
XSLT
XPATH
JAVA
…
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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?
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Resource Addressing through URI
 How to interact with dynamic, variable set of URI?
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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

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

Hyperlinks
 Can the state of a composition be bookmarked?
Follow hyperlinks
Generate hyperlinks
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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

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

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

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

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