Bicocca Restws Pautasso Talk

Web Services in 2008:
to REST or not to REST?
Cesare Pautasso
Faculty of Informatics
University of Lugano, CH
http://www.pautasso.info

19.6.2008 University of Milano Bicocca, Italy 3
©2008 Cesare Pautasso

Web Sites (1992)

Web HTML Web
Browser HTTP Server

WS-* Web Services (2000)

SOAP WSDL
Client XML Server
19.6.2008
(HTTP)
University of Milano Bicocca, Italy 4

1

RESTful Web Services (2007)

PO-XML
JSON

RSS
WADL
Web
Client
HTTP Server

WS-* Web Services (2000)

SOAP WSDL
Client XML Server
19.6.2008
(HTTP)
University of Milano Bicocca, Italy 5


2

RESTful RSS

XML JSON

MIME

URI HTTP

SSL

Is REST being used?
Slide from Paul Downey, BT


3

Can we really compare
WS-* vs. REST?

WS-* REST


Can we really compare
WS-* vs. REST?

WS-* REST

Middleware Architectural
Interoperability style for
Standards the Web


4

How to compare?

ral
Architectu ng
odeli
D ecision M REST

WS-* Architectural
style for
Middleware the Web
Interoperability
Standards


Architectural Decisions
• Architectural decisions Architectural Decision:
capture the main design Communication Protocol
issues and the rationale
behind a chosen technical Architecture Alternatives:
solution 1. TCP
• The choice between 2. SMTP
REST vs. WS-* is an 3. HTTP
important architectural 4. MQ
decision for 5. BEEP
integration projects
6. CORBA IIOP
• Architectural decisions 7. …
affect one another
Rationale

5

Application Integration Styles

Shared Remote Message Bus File
Database Procedure Transfer
Call

REST WS-*

Integration Technology Platform

Related Decisions (WS-*)

Call

REST WS-*


6

Related Decisions (RPC)

Call

REST WS-*


Decision Space Overview


7

Outline
21 Decisions and 64 alternatives
Classified by level of abstraction:
• 3 Architectural Principles
• 9 Conceptual Decisions
• 9 Technology-level Decisions

Decisions help us to measure the
complexity implied by the choice of
REST or WS-*

Architectural Principles

1. Protocol Layering
• HTTP = Application-level Protocol (REST)
• HTTP = Transport-level Protocol (WS-*)
2. Dealing with Heterogeneity
3. Loose Coupling


8

RESTful Web Service Example

HTTP Client Web Server Database
(Web Browser)

SELECT *
GET /book?ISBN=222 FROM books
WHERE isbn=222

POST /order INSERT
INTO orders
301 Location: /order/612

PUT /order/612 UPDATE orders
WHERE id=612

Big Web Service Example
(from REST perspective)
Web Service
HTTP Client Web Server
Implementation
(Stub Object)

POST /soap/endpoint
return getBook(222)

POST /soap/endpoint
return new Order()

POST /soap/endpoint
order.setCustomer(x)


9

Protocol Layering
• “The Web is the universe of globally • “The Web is the universal
accessible information” (tunneling) transport for messages”
(Tim Berners Lee) – Applications get a chance to
– Applications should publish their interact but they remain
data on the Web (through URI) “outside of the Web”

POX RSS JSON … SOAP (WS-*)

HTTP HTTP HTTP HTTP HTTP
SMTP MQ…
GET POST PUT DEL POST

Resource URI Endpoint URI

Application Application

Dealing with Heterogeneity

• Web Applications • Enterprise Computing
Picture from Eric Newcomer, IONA

HTTP

CICS
IMS


10

Conceptual Comparison


Technology Comparison


11

Measuring Complexity
• Architectural Decisions give a
quantitative measure of the complexity
of an architectural design space:
– Total number of decisions
– For each decision, number of alternative options
– For each alternative option, estimate the effort
REST WS-*
Decisions 17 14
Alternatives 27 35
Decisions with 1 or more alternative options


REST WS-*
Decisions 5 12
Alternatives 16 32
Decisions with more than 1 alternative options

REST WS-*
Decisions 17 14
Alternatives 27 35
Decisions with 1 or more alternative options

12


REST WS-*
Decisions 5 12
Alternatives 16 32

• URI Design
• Resource Interaction Semantics
• Payload Format
• Service Description
• Service Composition


REST WS-*
Decisions 5 12
Alternatives 16 32

REST WS-*
Decisions 12 2
Decisions with only 1 alternative option


13


• Payload Format
• Data Representation Modeling

REST WS-*
Decisions 12 2


Measuring Effort

REST WS-*
Do-it-yourself 5 0
Alternatives
Decisions with only do-it-yourself alternatives

REST WS-*
Decisions 12 2


14

Measuring Effort

REST WS-*
Do-it-yourself 5 0
Alternatives
Decisions with only do-it-yourself alternatives

• Resource Identification
• Resource Relationship
• Reliability
• Transactions
• Service Discovery

Freedom of Choice
Freedom from Choice


15

Comparison Summary
• Architectural Decisions measure complexity
implied by alternative technologies

• REST simplicity = freedom from choice
– 5 decisions require to choose among 16 alternatives
– 12 decisions are already taken (but 5 are do-it-yourself)

• WS-* complexity = freedom of choice
– 12 decisions require to choose among 32 alternatives
– 2 decisions are already taken (SOAP, WSDL+XSD)

Conclusion
• You should focus on whatever solution gets the
job done and try to avoid being religious about
any specific architectures or technologies.
• WS-* has strengths and weaknesses and will be
highly suitable to some applications and positively
terrible for others. Likewise with REST.
• The decision of which to use depends entirely on
the application requirements and constraints.
• We hope this comparison will help you make the
right choice.

16

References
• Cesare Pautasso, Olaf Zimmermann, Frank 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.

• Cesare Pautasso, BPEL for REST, Proc. of the 6th International
Conference on Business Process Management (BPM 2008),
Milan, Italy, September 2008.

• Cesare Pautasso, Gustavo Alonso: From Web Service
Composition to Megaprogramming In: Proceedings of the 5th
VLDB Workshop on Technologies for E-Services (TES-04),
Toronto, Canada, August 29-30, 2004.


17

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