1. REST – So What’s It All About?
CD110 @ SAP TechEd 2012
Las Vegas

2. About Me
Sascha Wenninger
Integration Guy: SOA, PI, etc.
Drawer of Diagrams, Writer of Emails
@sufw

3. Agenda
Applica.ons
Concepts
Demo
in
SAP-­‐land

4. Agenda
Applica.ons
Concepts
Demo
in
SAP-­‐land

5. REST

6. REpresentational
State
Transfer

7. What Does That Mean?

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

9. It’s
the
Web
(for
machines)

10. REST
interfaces
manipulate
the
state
of
resources
“Process
as
a
state
machine/data
flow
diagram”
Resource-­‐oriented
decomposi.on
of
business
processes
SOA-­‐style
interfaces
perform
a
specific
task
“Process
as
a
flowchart/workflow”
Func.onal
decomposi.on
of
business
processes

11. Representations?
The server can store its data in whatever way it likes
The client is unaware of this, and can store the same things
differently
Each party serialises its internal state into Representations
This provides loose coupling!

12. Everything has a URL

13. URLs because everyone understands them:
http://saperp.BlueT.com.au/customer/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

14. Why the http:// URLs?

15. HTTP is an Application Protocol.
REST recognises this.

16. But How is that Better than SOAP?

17. Remember the OSI Stack?
Layer
Example
7
Applica/on
DNS,
FTP,
HTTP,
etc.
6
Presenta.on
SSL
5
Session
L2TP,
PPTP
4
Transport
TCP
3
Network
IP
2
Data
Link
PPP,
ARP
1
Physical
IEEE
802.11

18. SOAP was designed
to be transport-protocol agnostic

19. Many bindings for SOAP:
HTTP
SMTP
JMS
AMQP

20. Many bindings for SOAP:
HTTP
SMTP
JMS
AMQP

21. HTTP
is
an
Applica.on
Protocol.
REST recognises this.

22. SOAP knows nothing about it!

23. So What?
Well, there are benefits to knowing…

24. Reliable Communication
(as long as the client knows how to
handle errors and retries)
Free* Caching!
*provided by commodity infrastructure!

25. Easy Metadata exchange via HTTP Headers!
Accept
Content-Type
If-Modified-Since
Last-Modified

26. …and last but not least…
A Universally-Understood Protocol!

27. HTTP has Standard Verbs
GET
PUT
POST
DELETE
HEAD
OPTIONS
PATCH
TRACE

28. HTTP has Standard Verbs
Standard Meaning
à Constraints = scope for
optimization
Widely Implemented
à Everybody knows how to behave

29. SOAP Doesn’t.
getAccountCustomerByInternalId
searchCustomerByBasicData
updateSalesProspectStatusByPartnerSalesRepresentativeBasicData_sync
And everything works via HTTP POST
(i.e. it uses HTTP as the dumb transport)

30. HTTP has Standard Responses
200 OK
302 Moved Permanently
404 Not Found
406 Method Not Allowed
409 Conflict
418 I’m a Teapot
…

31. SOAP Doesn’t.

32. One last principle before we move on:
HATEOAS

33. One last principle before we move on:
Hypertext
As
The
Engine
Of
Applica.on
State

34. An Example
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

35. Notice Something?
The Client is responsible for moving forward in a process
The server guides the client forward
(with ‘Check Out’, ‘Pay’ links)
The client is responsible for completing the process
If the client stops, the server doesn’t care!

36. Notice Something?
The server doesn’t maintain session/application state.
It does maintain resource state!
Every request modifies the state of a resource
In the example, the client causes the state of the “Shopping
Cart” resource to be modified.

37. Applica.ons
Concepts
Demo
in
SAP-­‐land

38. NetWeaver Gateway

39. RESTful OData API
Add-On to NetWeaver 7.0*
Web Devices Enterprise Social
Software
Current version: 2.0 SP05
Strategic for SAP SAP
NetWeaver
Gateway
SAP
Business
Suite
CRM SRM SCM PLM ERP
*see
Prerequisites
and
Deployment
Op.ons

40. The Good Things
• Exposes BAPIs, RFCs & custom ABAP classes via OData XML
– Specific connectors for BOL (GenIL), HANA, BW, BOR, Workflow, etc.
• Well integrated into SAP’s roadmap
– Tight integration with SUP 2.1+
– Duet Enterprise uses Gateway internally
• Framework provides flexible security and auditing/logging
• Push notifications to consumers after subscription
• Expose data & functionality from older (pre-7.0) systems

41. New Since Last Year
• JSON (finally! :-)
• Batch operations
• “Deltas”, aka conditional requests
• “Model Composition”, aka Mash-ups
• New Service Builder (SEGW)
• Idempotency Support
• etc… (see What’s New)

42. 2 Approaches to Development
Generation Tools OData Channel
• Quickly expose BAPIs, RFCs • Complete Control
and GUI screens • Build custom code adhering to
• Up & running in minutes! a structured framework with a
library of helper classes
• Since SP04: SEGW

43. 2 Approaches to Development
Generation Tools OData Channel
• Quickly expose BAPIs, RFCs • Complete Control
and GUI screens • Build custom code adhering to
• Up & running in minutes! a structured framework with a
library of helper classes
• New tool SEGW since SP04

44. The Limitations
• Only supports OData (both XML & JSON)
– no custom representations (other XML/JSON, PDF, etc.)
• Limited support for complex input parameters
• Inherits the limitations of the backend services

45. More Info on Gateway at TechEd
CD109 How the University of Mississippi Runs Better with NetWeaver Gateway
CD160 NetWeaver Gateway Development for Beginners
CD204 NetWeaver Gateway and OData in Detail
CD267 Developing Applications with HTML5 Toolkit and NetWeaver Gateway
MOB107 Best Practices for Establishing and Running a Mobile Landscape
MOB204 Building SAP Applications Using NetWeaver Gateway and HTML5
MOB205 From Start to Finish - Developing an iPad App Using NW Gateway
PMC206 NetWeaver PI and Gateway - When to Use What
TEC107 NetWeaver Gateway Overview - Roadmap and Strategy

46. Custom Development

47. DJ Adams Started It All!

48. A Simple RESTful API for SAP 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

49. 3 Resources
http://sapcrm:8000/api/businesspartner
http://sapcrm:8000/api/bprelationship
http://sapcrm:8000/api/opportunity
plus any sub-resources we need

50. 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 ßà JSON library on CodeExchange!

51. Sidebar: Hyperlinks in JSON

52. Sidebar: Hyperlinks in JSON
No one standard to show hyperlinks
à We chose the simplest option we found:
magic
keyword
rela.onship*
“links”: {
“self”: “http://…”,
custom
rela.onship
link
URL
“up”: “http://…”,
“http://auspost.com.au/api/doc/rels/tracking”: “http://…”,
…
} *as
per
IANA
standard

53. ICF Configuration in SAP CRM
Create
a
public
class

54. ICF Configuration in SAP CRM
Assign interface IF_HTTP_EXTENSION

55. Insert Code Here…

60. Demo

61. Summary
• REST is an architectural style
– Apply web principles to A2A integration
– Promotes true loose coupling via hyperlinks
– Based on Resources rather than functionality or tasks
• NetWeaver Gateway can expose SAP data & functionality in
a RESTful way.
• More specific requirements can be met with Z code
• Most mobile frameworks rely on RESTful integration
– But the REST style is equally valid for A2A and non-mobile scenarios!

62. About Me
Sascha Wenninger
sascha@BlueT.com.au
@sufw

63. Get the Latest Version of this Talk!
http://slideshare.net/sufw
This
presenta.on
by
Sascha
Wenninger
is
available
under
a
Crea.ve
Commons
A`ribu.on-­‐ShareAlike
3.0
license

64. Feedback
Please complete a session evaluation for this session
Session Code: CD110

65. Resources & Further Reading
A free eBook on REST, by InfoQ: http://www.infoq.com/minibooks/emag-03-2010-rest
Other interesting blogs and articles on InfoQ:
http://www.infoq.com/articles/RESTSOAFuture
The Richardson Maturity Model, explained by Martin Fowler: http://martinfowler.com/articles/richardsonMaturityModel.html
...and by Leonard Richardson himself: http://www.crummy.com/writing/speaking/2008-QCon/act3.html
DJ Adams’ original blog on REST on SCN:
http://scn.sap.com/people/dj.adams/blog/2004/06/24/forget-soap--build-real-web-services-with-the-icf
Further blogs by DJ on implementing RESTful services via the ICF:
http://scn.sap.com/people/dj.adams/blog/2009/09/21/a-new-rest-handler-dispatcher-for-the-icf
http://scn.sap.com/people/dj.adams/blog/2010/01/07/representational-state-transfer-rest-and-sap
http://scn.sap.com/people/dj.adams/blog/2009/09/30/rest-orientation-controlling-access-to-resources
A Simple Intro to JSON: http://json.org
CORS – Cross-Origin Resource Sharing, by the Mozilla Developer Network:
http://hacks.mozilla.org/2009/07/cross-site-xmlhttprequest-with-cors/

66. Resources & Further Reading
RESTful APIs from Scratch – Lessons Learnt (so far):
http://scn.sap.com/community/technology-innovation/blog/2012/06/03/restful-apis-from-scratch-lessons-learnt-so-far
The NetWeaver Gateway space on SCN: http://scn.sap.com/community/netweaver-gateway
HTTP: An Application-Level Protocol: http://dev.opera.com/articles/view/http-basic-introduction/
HTTP: Let’s GET It On!: http://dev.opera.com/articles/view/http-lets-get-it-on/
HTTP: Response Codes: http://dev.opera.com/articles/view/http-response-codes/
Resources are not Objects: http://ruben.verborgh.org/blog/2012/09/27/the-object-resource-impedance-mismatch/
(a good read for OO programmers)
Known Limitations of SAP NetWeaver Gateway: SAP Note 1574568

67. Attributions
Images by Geek & Poke (Oliver Widder):
http://geekandpoke.typepad.com/.a/6a00d8341d3df553ef0133f3e30a99970b-pi
http://geekandpoke.typepad.com/.a/6a00d8341d3df553ef0105362b2664970c-pi
http://geekandpoke.typepad.com/.a/6a00d8341d3df553ef015390312d9f970b-pi
‘Standards’ by xkcd (Randall Munroe): http://xkcd.com/927/
‘Permanent State’ by Gaping Void (Hugh MacLeod): http://gapingvoid.com/2011/07/28/permanent-state/
Many thanks to all for providing their work under a Creative Commons license! J