BPM with REST

Business Process Management
with REST
Cesare Pautasso
Faculty of Informatics
University of Lugano, Switzerland

c.pautasso@ieee.org
http://www.pautasso.info
@pautasso

BPM REST

©2010 - Cesare Pautasso 2

Business
RESTful
Process
Web Services
Management


WS-* Standards Stack

©2009-2010 - Cesare Pautasso - 30.6.2010 4

WS-* Standards Stack

BPM Management
Interoperability

Transactions
Security
Reliability
Metadata

State
Messaging

©2009-2010 - Cesare Pautasso - 30.6.2010 5

BPM Management
Interoperability

Transactions
Security
Reliability
Metadata

State
Messaging
Can you do it
with REST?

From REST-* (JBoss)

“ We believe there is huge potential to

http://www.jboss.org/reststar/specifications/workflow.html
marrying REST with workflow and BPM.
[…]
Combined with the architecture of the Web,
a workflow service can provide both a truly
simple, portable, and flexible way to build
workflow driven integrations and

”
applications.


BPMN/WS-BPEL
Workflow Workflow
Process Model Users/Clients Participants
Act 2 Act 4

Act 1 Act 5 Act 7

Act 3 Act 6

Workflow Management Engine
Workflow
Modelers
Adapters Bus

Applications Web
Services

Databases


WS-BPEL Primitives

Web <receive>
<invoke>
Service <reply>

<invoke> Web
<receive>
Service

 The modeling language natively supports
the RPC or message-based connectors


What is your SOA connector today?

RPC ESB

REST/HTTP


REST as a new connector

RPC ESB
Publish/Subscribe
Call

REST/HTTP

Get/Put/Post/Delete


Is REST really used?
Atom, 2%
Gdata, 1%
XMPP, 0%
JavaScript, 6%
XML-RPC, 2%
SOAP, 17% JSON-RPC, 0%

SMS, 2042 APIs
0%
RSS, 1%
ProgrammableWeb.com
30.6.2010
REST,
71%


REST in one slide
 Web Services expose their
data and functionality trough PUT
resources identified by URI
R
 Uniform Interface Principle: GET
Clients interact with resources POST
through a fix set of verbs. DELETE
Example HTTP:
GET (read), PUT (update), DELETE, POST (catch all),
 Multiple representations for the same resource
 Hyperlinks model resource relationships and valid
state transitions for dynamic protocol description
and discovery

Workflow Workflow
Process Model Users/Clients Participants
Act 2 Act 4

Act 1 Act 5 Act 7

Act 3 Act 6

RESTful Workflow Management Engine

PUT

GET
R Adapters Bus

Applications Web
Services
POST
DELETE Databases


BPM with REST

Process Model
Publishing
Act 2 Act 4 R Processes
Act 1 Act 5 Act 7
as Resources
Act 3 Act 6


RESTful
Service
R R R Composition


BPM with REST
Publishing
This talk will R Processes
focus here as Resources


RESTful
Service
R R R Composition


Some Challenges for BPM engines
 Can you drive the execution of tasks with
PUT/POST/DELETE requests?
 Can you monitor your processes with an
RSS/ATOM feed?
 Can you bookmark a process instance?
 Can you send an email to your colleague with a
link to a task from your worklist?
 Can you ask a process to give you links to its
tasks left to be done?
 Can you publish your process as a resource?
 Can you publish resources from your process?
 Can you call RESTful APIs directly?

BPM REST
 Processes  Resources/URIs
 Tasks  Uniform
 Control Flow Interface
 Data Flow  Representations
…  Hypermedia


Everything is a resource
/process/X /process/X/1

Process
Process
Instance

Task
Task
Instance
/task/Y
/task/Y/1


Hypermedia
/process Process
Process
Instance
GET
/process/name Task
Task
Instance
GET
/process/name/instance

GET
/process/name/instance/taskname

Follow links to discover the processes
deployed as resources

Representations
Web page
with form to start List of process
a new process input parameters
instance ContentType: ContentType:

text/html application/xml
GET /process/name
ContentType: ContentType:
text/plain application/json
ContentType:
Basic textual Process
description image/svg+xml metadata
of the process in JSON


Uniform Interface and Hypermedia
List the
GET /process deployed Get a form
processes describing how
GET /process/name to start the
process
Start a new
POST /process/name process
instance Check what
is the state
GET /process/name/instance of the
instance
DELETE /process/name/instance
Clean up
(once it is done)

Starting or Running a new process?
/process  Should the client be kept
waiting for the process to run
until completion?
POST /process

200 OK  Clients may want to block until
(Process the whole process has
Finished completed its execution
Reply) (or it decides to reply to them)

Starting or Running a new process?
/process  The client starting a long
running process is redirected to
a location x representing the
POST /process newly started process instance
 The process and the client run
202 Accepted asynchronously
Location: x
 The client may retrieve the
current state of the process
GET /process/x instance at any time

200 OK


Uniform Interface and Hypermedia
GET /task List the
active tasks Get a form
describing how
GET /task/name/instance to perform the
task
Finish
POST /task/name/instance
the task

GET /task/name/instance Get the final
representation
of the completed
… task


POST or PUT?
GET /task Note:
PUT could also be
used here
GET /task/name/instance to set the state
(Finished, Failed)
of the task
POST /task/name/instance

GET /task/name/instance

…


Example: RESTBucks

Jim Webber, Savas Parastatidis, Ian Robinson http://restinpractice.com/ 27

Simple RESTBucks Example

POST
/rest/restbucks/order/1.0/
/rest/restbucks/order/1.0/{id}
GET
/tasks/restbucks/order/1.0/{id}/payment

POST
GET

/receipt/{uuid}


Simple RESTBucks Example
Hypermedia-centric service design (and implementation)
done with a business process model

Private Tasks
Resources


Instantiating a process
GET /rest/restbucks/order/1.0/

Retrieve a form which describes how to instantiate a new process

Instantiating a process
POST /rest/restbucks/order/1.0/

Run = blocking
(client waits until
Start = non blocking the process replies)
(redirect to URI of
the new instance)

Interacting with a task
GET
/task/restbucks/order/1.0/0/payment


Interacting with a task
POST /rest/restbucks/order/1.0/0/payment


Interacting with a resource
GET /receipt/2fc7f6e2-8b43-4672-a7c4…


Interacting with a resource
DELETE /rest/restbucks/order/1.0/0


Deleting a process resource
DELETE /rest/restbucks/order/1.0/0


Viewpoints

Control Data
Flow Flow
Service
Bindings

REST.TASK REST.URI REST WS-* SQL …

Control
Flow

Control Flow
Dependency


Service
Bindings

SQL

WS-*

REST

REST.URI

REST.TASK


REST.TASK

Specify the final state
of the Payment task


REST.URI

Specify the state
associated with the URI


Data
Flow

Data Flow
(Copy)


Static vs. Dynamic Typing
 Myth: RESTful Web services cannot be
composed (with BPEL) because they do
not give a static contract description
 Reality: RESTful Web services can
dynamically negotiate the most
suitable representation format with
their clients
 Challenge: How to support dynamic
typing and content type negotiation in a
BPM composition language?


Active Resources
 Myth: Processes cannot be mapped to
resources because they can change
their state (independently of their
clients)
 Reality: REST Resources do not have to
be passive “CRUD” services but can be
active and have a life of their own.
 Challenge: How to best let clients
control an active resource backed up
by a process instance through the
uniform interface?

Synchronous vs. Asychronous
 Myth: Processes run for a long time
and need to interact asynchronously
with their clients. This cannot be done
with HTTP.
 Reality: HTTP supports non blocking
interactions. Each process instance is
mapped to a resource URI, which can
be used by clients throughout its
lifetime.
 Challenge: How to let processes send
notifications back to their clients?

Conclusions
 REST resources are a good abstraction
to publish processes on the Web
 RESTful HTTP is good enough to
interact without any extension with
process execution engines and drive
the execution of process and task
instances
 If done right, BPM can be a great
modeling tool for Hypermedia-centric
service design
(and implementation!)

More Information

Cesare Pautasso
Faculty of Informatics, USI Lugano
http://www.pautasso.info/
@pautasso

JOpera
RESTful Process Engine
http://www.jopera.org/
@jopera_org

References
 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 7th International
Conference on Business Process Management
(BPM 2008), Milano, Italy, September 2008
 C. Pautasso, Composing RESTful Services with JOpera,
In: Proc. of the International Conference on Software
Composition (SC2009), July 2009, Zurich, Switzerland.
© 49

Conclusion

Raj Balasubramanian,
 Applying the SOA composition principle to
Benjamin Carlyle,
Thomas Erl,
REST gives interesting results Pautasso,
Cesare
 Thanks to hyperlinks, REST SOA with a new
brings REST,
(more dynamic and loosely coupled)
Prentice Hall,
twist to SOA composition to appear in 2011
 Composing RESTful services helps to build
mashups, but is different
 A RESTful API is the perfect abstraction for
publishing the state of a workflow


BPM with REST

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