Slides from J and Beyond 2013 presentation. You have probably heard of REST and Web Services. In this presentation you will learn what they are and why they are important to the future of Joomla. You will learn why it is important for the API to be HAPI, what the HATEOAS constraint is and why developers should always keep it in mind when writing clients and servers on the new API, and why moving to a services-first design philosophy is important for everyone involved in Joomla software development.

1. and being HAPI
Taking a REST
Chris Davenport
Joomla Production Leadership Team

2. Architectural Style of the Web
"The World Wide Web has succeeded in large
part because its software architecture has been
designed to meet the needs of an Internet-
scale distributed hypermedia system."
Fielding, Roy Thomas. Architectural Styles and the Design of Network-based Software Architectures.
Doctoral dissertation, University of California, Irvine, 2000.

3. Web experiences growing pains

4. Web standards adjusted
Fielding: Analysis of network-based software
architectures
● Key constraints give rise to desired
properties
● Internet-scale distributed hypermedia
Adjustments/corrections made
● HTTP/1.1 RFC 2616
● Uniform Resource Identifiers RFC 3986
● and others

5. Web saved! Hurray!
(2008: Google reaches 1 trillion unique URLs)

6. What is REST?
2000: Fielding's PhD dissertation
● REST (Representational State Transfer)
● Architectural style for building scalable,
distributed, hypermedia applications.
● The architectural style that has been used
to guide the design and development of
the World Wide Web's architecture.

7. REST constraints
● client-server
● stateless
● cache
● uniform interface
● layered system
● code-on-demand (optional)
The important point is to not unintentionally
violate these constraints.

8. Client-server
Client and server may be
● developed at different times
● by different people
● evolving at different rates
But they must always have a
Shared Understanding

9. Resource-based
Resources are identified by URIs:
www.example.com/articles/1234
Note: This might be the same resource at some point in time:
www.example.com/articles/latest-news

10. Manipulation of resources via
representations
Ceci n'est pas une pipe
Translation: "This is not a pipe"

11. Self-descriptive messages
There must be enough information in each
message for the recipient to understand it.
Self-contained messages have their limits.
There will always be out-of-band information
needed to understand messages. The problem
is where to draw the line.

12. Hypermedia constraint
Hypermedia as the engine of application state
● Clients drive application state by
○ following hypermedia links
○ or submitting forms
● Clients should treat URL's as opaque
○ except for URI Templates (RFC 6570)
● Fielding: "Servers must have the freedom to
control their own namespace"
○ Servers can change URIs without breaking clients

13. What about Joomla?
Shared
code
Site
Admin
Modules
Web
browser
HTML
Server (Joomla)Client

14. What about Joomla?
Shared
code
Site
Admin
Modules
Web
browser
HTML
Server (Joomla)Client
AJAX
JSON

15. What about Joomla?
● Mobile (and other) devices
● Internet of Things
● Open data
● Integrating business processes
● Electronic Data Interchange (EDI)

16. Joomla is an information silo
Components can't easily
communicate with each other

17. Joomla Hypermedia Services
● Break Joomla components/modules into
smaller "services".
● Services have a uniform interface
○ JInput for input
○ JSON, XML, HAL, etc. for output
● Services communicate using media types
○ application/vnd.joomla.*
○ Additional constraints using schemas/profiles

18. Joomla Next?
Services
Device
Server
HAL
HAL
HAPI
Server (Joomla)

19. application/hal+*
Resource representation
_embedded _links
rel href
rel href
rel href

20. Joomla Next?
Services
Site UI
Admin
UI
Web
browser
HTML
HTML
HAL
HAL
Server (Joomla)
Client
HAPI

21. Joomla Next?
Services
Site UI
Admin
UI
Web
browser
AJAX
HAL
HTML
HTML
HAL
HAL
Server (Joomla)
Client
HAPI

22. Joomla Next?
Services
Site UI
Admin
UI
HAL
HAL
Server (Joomla)Client
Web browser
HAPI

23. Joomla Next?
Services
Device
Server
HAL
HAL
Server (Joomla)
CLI
HAL
Daemon
HAL
HAPI HAPI

24. Joomla Next?
ServicesUI
Web browser
HTML HAL
Server (Joomla)Client
HAPI
Services
HAL
Another server
HAPI
UI

25. What's inside a service?
Services
Server (Joomla)
HAPI
C
M
V
RAD/SDK/FoF
CLI
Drupal 8
HAPI

26. Web Services Working Group
http://docs.joomla.org/Web_Services_Working_Group
● Web Services Specification
○ currently at second draft
● Sample code
○ based on new MVC in Joomla 3.x
○ structure allows it to be retrofitted to any component
without touching existing code
○ articles, weblinks, categories
○ can be browsed with any generic HAL client

27. application/vnd.joomla.*+hal+*
Resource representation
_embedded _links _meta
rel href
rel href
rel href

28. Hierarchy of media types
JSON
HAL
vnd.joomla.service
vnd.joomla.list
vnd.joomla.item
XML
Remember: Shared understanding

29. WSWG Next Steps
http://docs.joomla.org/Web_Services_Working_Group
● Web Services Specification
○ more people to read and comment
● Coding
○ more people to write code for a J3.x implementation
○ client SDK (JavaScript and PHP versions)
● Future
○ more people to work on an architecture for Joomla
beyond the 3.x cycle

30. Questions?
Play with a demo at
http://demo.davenporttechnology.com/api/hal-browser/browser.html#http://demo.davenporttechnology.com/api
Thank you for listening

31. Image credits
http://commons.wikimedia.org/wiki/File:Paris_-_Jardin_du_Luxembourg_-_le_soir.JPG License: GNU
FDL
http://en.wikipedia.org/wiki/File:Crying-girl.jpg License: CC-A-SA 2.0
http://www.veezzle.com/photo/1529836/Class-of-2007-USAF-Academy-Graduation-Hat-Hurray-Toss-
Thunderbird-Fly-Over License: CC-A 3.0
http://en.wikiversity.org/wiki/File:Alvano-Sabina-pipe.jpg License: GNU FDL
http://commons.wikimedia.org/wiki/File:Ralls_Texas_Grain_Silos_2010.jpg License: Public domain