Explaining the SOA/REST impedance mismatch

W I L L I A M M A R T Í N E Z P O M A R E S

EXPLAINING THE SOA/REST IMPEDANCE MISMATCH

AGENDA

Needs and Architectural Styles

Application Types

Mismatches!

Vice versa: The Service As A Resource option

2011 William Martínez Pomares Avantica Technologies UCR 2

CONCEPTS. NAMES.

2011 William Martínez Pomares

Avantica Technologies UCR3

NEEDS AND ARCHITECTURAL STYLES



Styles are created to support needs

Styles define actors, component types, relations

Styles impose restrictions, constrains

Styles are the why and a macro how

Styles chosen for application types and needs

APPLICATION TYPES



Distributed

Networked

Integrated

DISTRIBUTED APPLICATION

oApplication as a

Whole

o Tight connections

o High speed

communication

o Strong coupling

o Reuse of Parts

Optional



NETWORKED APPLICATION

• Application as a Composition of Nodes

• Weak coupling

• High cost communication

• User aware of composition

• Reuse of Parts is common



INTEGRATED APPLICATION

• Application as an Integration of Whole Applications

• Standard Interfaces

• Low frequency of interaction

• Higher level processes

• Reuse of Parts is rule

• Large distribution



SOA SOLVES…



SOA – Large Distributed System*

• Legacy

•Heterogeneous

•Complex

• Imperfect

•Redundant

•Business service, process oriented*Nicolai M. Josuttis, SOA in Practice, OREILLY

REST SOLVES



REST - Large Grain Hypermedia Transfer *

•Low Entry-barrier

•Extensibility

•Distributed Hypermedia

• Internet-scale

•Anarchic Scalability

• Independent Deployment

*Roy Thomas Fielding, Architectural Styles and the Design of Network-based

Software Architectures, 4

SOA SOLUTION



Client

Service

Service

Service

Client

Repository

Flo

w

REST SOLUTION



Client

Client

Server

Server

Server

COMPARING… MISMATCH!

SOA

• Messaging: Send data to a service for processing. RPC?

• No operation in protocol

• Business as a process, not as data

• Processes as resources

• Discoverable by repository, centralized

• No flow control. External or out of band

• Business semantics

REST

• Messaging: Send/Receive representation. No RPC.

• Finite Operation set in protocol

• Not about business

• Datum as resources

• Discoverable by link, distributed

• Hypermedia as the State Engine

• Mixed semantics



REST – SOA MATCH UP



Different Application Types

Both Use Uniform Interface, just Different one!

Each style can use the other internally

Use implies impedance mismatch

Client and server have different tasks

None is easier!

SOA AND REST WEB SERVICES



REST as Special Service construction architecture

• Large distributed data

•Hypermedia related or Insensible to format transformation.

•Relaxed Security

• Independent evolution requirement

•Non processing intensive

•Non sensitive to performance hits, cacheable.

REST AND SERVICE AS A RESOURCE



WSA and the Resource View

•A Service has an ID

•Get will return the services description doc (SDC).

•SDC contains links with flow and document semantic rules

• (Call SDC the WSDL)

•Service Usable in any RESTful Interaction

CONCLUSION



Two styles, Not incompatible

Check semantics and business abstraction level

Use SOA for business oriented, centralized control needs

Use REST for data oriented, dynamic topology needs

Study carefully interactions and mismatch cost

Explaining the SOA/REST impedance mismatch

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