REST: So What's It All About? (Mastering SAP Technologies 2012)

REST: So What’s It All About?
Sascha Wenninger (@sufw)

What You Will See

As a paradigm for designing application integration and APIs,
REST now enjoys significantly greater popularity than SOA(P),
particularly for public, internet-facing APIs.
This presentation will give you a quick overview of the core principles
behind the architectural style known as REST.
You will also get a taste of two different approaches for implementing
interfaces according to REST principles in your SAP systems.

Mastering SAP Technologies

A Quick Definition

Architectural Style
“An architectural style is a coordinated set of architectural
constraints that restricts the roles/features of architectural elements
and the allowed relationships among those elements within any
architecture that conforms to that style.”
Roy Fielding, p. 13


Agenda

NetWeaver Custom
Concepts Demo
Gateway Coding

Implementation Options


REST


REpresentational
State
Transfer

What Does That Mean?


One Definition…

The Client communicates with the Server
by modifying the state of Resources
through Representations


Another Definition…

It’s The Web

(for Machines)


A Different Approach

REST interfaces manipulate the state of resources
“Process as a state machine/data flow diagram”
Resource-oriented decomposition of business processes

SOA-style interfaces perform a specific task
“Process as a flowchart/workflow”
Functional decomposition of business processes


Representations?

A Representation is a serialised version of the server’s internal state

Provides abstraction from implementation (DB, frameworks, language)

Dynamically-created web pages are Representations!

Many different formats possible – not just XML!


Identifying Resources

Every Resource has an ID


Identifying Resources

URLs because everyone understands them:
http://saperp/accountcustomer/12345

URLs are cheap. Use lots of them!
http://api.netflix.com/catalog/titles/movies/60021896
http://api.netflix.com/catalog/titles/movies/60021896/cast
http://api.netflix.com/catalog/titles/movies/60021896/synopsis

HTTP?

Why the http://… URLs?


HTTP!

Layer Example

HTTP is an Application Protocol 7 Application DNS, FTP, HTTP...
6 Presentation SSL
5 Session L2TP, PPTP
REST uses it as such
4 Transport TCP
3 Network IP
SOAP uses it as a dumb transport 2 Data Link PPP, ARP
1 Physical IEEE 802.11


This has a number of benefits…


Benefits

Reliable Communication
(The client must handle errors and retries)

Free* Caching!

*provided by commodity infrastructure!

Mastering SAP Technologies Thanks, Oliver Widder!

Benefits

Easy Metadata Exchange via HTTP Headers!

Accept
Content-Type
If-Modified-Since
Last-Modified
…


Benefits

…and last but definitely not least…

A Universally-Understood Protocol!


But How is that Better than SOAP?


No Special Tools Needed!


HTTP Has Standard Verbs…

GET
PUT
POST
DELETE
HEAD
OPTIONS
PATCH
TRACE

SOAP Doesn’t.

getAccountCustomerByInternalId
searchCustomerByBasicData
updateSalesProspectStatusByPartnerSalesRepresentativeBasicData_sync

And everything works via HTTP POST
(i.e. it uses HTTP as a dumb transport protocol)


Standard Verbs

Standard Meaning
 Constraints = scope for optimization
 HTTP GET probably the most optimised piece of code ever

Widely Implemented
 Everybody knows how to behave
 No need to code low-level, API-specific communication logic


HTTP Has Standard Responses…

200 OK
302 Moved Permanently
404 Not Found
406 Method Not Allowed
409 Conflict
418 I’m a Teapot
…


SOAP Doesn’t.


Benefits

One more:
HATEOAS


Benefits

One more:
Hypertext
As
The
Engine
Of
Application
State

HATEOAS for Humans

Client requests Shopping Cart

Server sends HTML page with items and links
Client’s move
Client clicks the “Check Out” link

Server sends HTML page with Total Amount
Client’s move
Client clicks the “Pay” link

Server sends HTML page with “Thank You” message

Things to Note

The Server guides the Client forward in the process
(with ‘Check Out’, ‘Pay’ links, etc.)

The Client is responsible for moving forward
If the client stops, the server doesn’t care


NetWeaver Custom
Concepts Demo
Gateway Coding

Implementation Options


NetWeaver Gateway

REST-inspired OData API
Add-On to NetWeaver 7.02
Current version: 2.0 SP03 Web Devices Enterprise
Software
Social

Strategic for SAP
SAP NetWeaver Gateway

SAP Business Suite

CRM SRM SCM PLM ERP


The Good Things

• Quickly build very simple RESTful APIs
• Exposes BAPIs or custom ABAP classes via OData XML
• Core part of SAP’s roadmap (integration to SUP, Duet, etc.)
• SAP-delivered content with each SP release
• Detailed logging and performance analysis tools
My take: A productivity framework similar to the Web Services Runtime
in ABAP

The Limitations

• Only supports OData (Open, but Microsoft-centric XML)
– JSON-formatted OData available with SP04 (May 2012)
– no custom representations (other XML, PDF, etc.)
• Limited support for complex input parameters (e.g. forms)
• Anything beyond really basic APIs will require custom code
– …maybe even lots of code…
• Licensed separately


Mapping to BAPIs

BAPI Field Defaults OData XML Field


OData Channel

Programmatic way of exposing OData from the backend
Much more flexible – full HATEOAS implementation possible!
Full feature set available in SP04 (May 2012)


DJ Adams Started It All…

Mastering SAP Technologies DJ Adam’s SCN Blog

A Simple REST API for CRM

• BusinessPartners everywhere
• BPs have roles (e.g. Customer, Contact Person, Employee…)
• BPs have relationships with other BPs
• Relationships have attributes
• Relationships lead to Opportunities

Target consumer: Mobile app built with HTML5 + jQuery Mobile


3 Resources

http://sapcrm:8000/auspost/businesspartner

http://sapcrm:8000/auspost/bprelationship

http://sapcrm:8000/auspost/opportunity

plus any sub-resources we need


Design Principles
JSON as the default format
Roles & Relationships via hyperlinks
Client must only know the ‘entry point’ URL to its own BP
All other client interaction driven by hyperlinks

There is a great ABAP  JSON library on CodeExchange!

ICF Configuration

Create a public class

ICF Configuration

Assign Interface IF_HTTP_EXTENSION


Insert Code Here.


Questions


Key Points to Take Home

• REST is an architectural style – not a protocol or product.
– Applies web principles to A2A integration, including use of hyperlinks

• NetWeaver Gateway can quickly expose SAP data & functionality in a
RESTful way.
• More specific requirements can be met via custom code, including
the ADL (Alternative Dispatch Layer)
• Most mobile frameworks rely on RESTful integration

If You’d Like to Learn More
A free eBook on REST, by InfoQ: http://www.infoq.com/minibooks/emag-03-2010-rest
A Pragmatic Introduction to REST, by Stefan Tilkov
Teach a Dog to REST, by Apigee’s Brian Mulloy
REST: putting the web back in to web services, by Kerry Buckley
DJ Adams’ original blog on REST on SDN: Forget SOAP - build real web services with the ICF
Further blogs by DJ on implementing RESTful services via the ICF:
• REpresentational State Transfer (REST) and SAP
• A new REST handler / dispatcher for the ICF
• REST-orientation: Controlling access to resources

The defining work on REST, by Roy FieldingArchitectural Styles and the Design of Network-based Software Architectures
A Simple Intro to JSON: http://json.org
Known Limitations of SAP NetWeaver Gateway: SAP Note 1574568
The Richardson Maturity Model, and explained by Martin Fowler.


watchKeynote();


We’re RESTful now

GET /masteringsap/tech/keynote HTTP/1.1


Sascha Wenninger
Australia Post
sascha@wenninger.name
@sufw
+61 403 933 472

Mastering SAP Technologies Slide 59

REST: So What's It All About? (Mastering SAP Technologies 2012)

REST: So What's It All About? (Mastering SAP Technologies 2012)

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