Let's have a RESTful conversation

Cesare Pautasso
http://www.pautasso.info
[email protected]
@pautasso

University of Lugano (USI)

Faculty of Informatics

Opened 2004
25 Professors
125+ PhD/Postdoc researchers
Research: Software, Systems and Services Engineering
Award-winning Innovative Teaching Curriculum

Architecture, Design and Web Information Systems Engineering

BenchFlow - a benchmark for workflow engines
Liquid Software Architecture
ASQ - Interactive Scalable Lectures
Parallel JavaScript/Multicore Node.JS
SAW - Collaborative Architectural Decision Making
NaturalMash - Web Service Composition with Natural Language

http://design.inf.usi.ch

Abstractions

Microservices

Interfaces

Conversations

Multiple interactions (message exchanges) between two or more participants to achieve a goal

G. Hohpe

What is REST?

RESTful Conversations

Examples

?

GET /booking/42?payment HTTP/1.1

HTTP/1.1 302
Link: </payment?booking=42>; rel="payment"

GET /payment?booking=42 HTTP/1.1

HTTP/1.1 200

Long Running Task

POST /slow HTTP/1.1

HTTP/1.1 202 Accepted
Location: /slow/42

...

GET /slow/42

HTTP/1.1 200

...

GET /slow/42

HTTP/1.1 303 See Other
Location: /result/42

GET /result/42

HTTP/1.1 200

Try-Confirm/Cancel (TCC)

Try to reserve multiple resources

POST /telephone HTTP/1.1
Host: api.swisscom.ch

HTTP/1.1 201 Created
Location: /telephone/0586664302

POST /bill HTTP/1.1
Host: api.post.ch

HTTP/1.1 201 Created
Location: /bill/42

If everything is successful, confirm the bookings

PUT /telephone/0586664302 HTTP/1.1
Host: api.swisscom.ch
Accept: application/tcc

HTTP/1.1 204 No Content

PUT /bill/42 HTTP/1.1
Host: api.post.ch
Accept: application/tcc

HTTP/1.1 204 No Content

RESTful Conversation

Link: </payment?booking=42>; rel="payment"

Services control the conversation by embedding links into representations/responses

Clients drive the conversation by deciding which link to follow

Services only reveal the immediate next steps

Clients need to understand the link relation semantics to choose the link to follow

How to model RESTful Conversations?

BPMN

Software Connectors

BPMN and Software Connectors

Real World Example

AirBnB Conversation

GuestAirBnBHost

State (in)visibility

Where can you find the reservation in the model?

At the end, one Participant gets notified, the other just knows the outcome

Interaction abstraction

email notifications for state changes driven by HTTP POST (form submission) or timeouts

What if a participant wants to track the progress, check the status?

What if a participant wants to cancel the reservation?

Hypermedia

email notifications for state changes include a hyperlink to continue the conversation with other form submissions (HTTP POST)

How is the link correlated with the process/task instance?

Modeling Challenges

Define resource lifecycle (creation, destruction, updates and allowed state transitions)

Represent how to embed hypermedia controls (links, forms) as part of messages/representations

BPMN 2 Choreography

RESTful Choreography

Modeling Challenges

Define resource lifecycle (creation, destruction, updates and allowed state transitions)

Represent how to embed hypermedia controls (links, forms) as part of messages/representations

Capture recurring conversation patterns

(Some) Conversation Patterns

Redirection
Long Running Requests
Collection Navigation
Collection Item Lifecycle
Editable Resource
Try-Confirm/Cancel
Post Once Exactly
Protected Resource

Redirection

Editable Resource

Long Running Request

RESTful conversations

REST services engage in conversations, steered by hyperlinks embedded in resource representations
How to capture the conversation flow, modeling resource lifecycles and hypermedia types? (BPMN?)
We have started to collect recurring conversation patterns: let us know if you spot some in your RESTful API

References

C. Pautasso, A. Ivanchikj, S. Schreier, "Modeling RESTful Conversations with extended BPMN Choreography diagrams", 9th European Conference on Software Architecture (ECSA 2015), Dubrovnik, Croatia, Springer, September, 2015.
F. Haupt, F. Leymann, C. Pautasso: A conversation based approach for modeling REST APIs, 12th Working IEEE / IFIP Conference on Software Architecture (WICSA 2015), Montreal, CA, May 2015
J. Bellido, R. Alarcon, C. Pautasso, Control flow patterns for decentralized RESTful service composition, ACM Transactions on the Web, 8(1):5, December 2013 doi:10.1145/2535911
T. Erl, B. Carlyle, C. Pautasso, R. Balasubramanian, SOA with REST: Principles, Patterns & Constraints for Building Enterprise Solutions with REST, Prentice Hall, August 2012, ISBN 9780137012510
C. Pautasso, RESTful Web Service Composition with JOpera, Proc. of the International Conference on Software Composition (SC 2009), Zurich, Switzerland, July 2009
A. Gambi, C. Pautasso, RESTful Business Process Management in the Cloud, Proc. of the 5th ICSE International Workshop on Principles of Engineering Service-Oriented Systems (PESOS 2013), San Francisco, USA, May 2013
C. Pautasso, BPMN for REST, In Proceedings of the 3rd International Workshop on BPMN (BPMN 2011), Lucerne, Switzerland, November 2011
C. Pautasso, RESTful Web Service Composition with BPEL for REST, Data & Knowledge Engineering, Volume 68, Issue 9, September 2009, Pages 851-866, doi:10.1016/j.datak.2009.02.016.

Ack: Gregor Hohpe, Silvia Schreier, Ana Ivanchikj, Florian Haupt, Frank Leymann, Mathias Weske, Adriatik Nikaj, Sankalita Mandal, Guy Pardon

GuestAirBnBHost

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