WS-REST 2013 Distributed Affordance An Open-World Assumption for Hypermedia Ruben Verborgh, Michael Hausenblas, Thomas Steiner, Erik Mannens, Rik Van de Walle

1. Distributed
Affordance
An Open-World Assumption
for Hypermedia
Ruben Verborgh, Michael Hausenblas,
Thomas Steiner, Erik Mannens,
Rik Van de Walle
The three princes of Serendip

2. RESTarchitectural style
different?
What makes the

3. HATEOAS
Hypermedia As The Engine
Of Application State

4. Representations contain
the links to next steps.
How can the server know
what the client’s next steps are?

5. Distributed Affordance
An Open-World Assumption
for Hypermedia
Problem statement
Concept and Architecture
Demo

6. Distributed Affordance
An Open-World Assumption
for Hypermedia
Problem statement
Concept and Architecture
Demo

7. Hypertext [is] the simultaneous presentation
of information and controls such that
the information becomes the affordance
through which the user (or automaton)
obtains choices and selects actions.
— Roy T. Fielding

8. Hypertext [is] the simultaneous presentation
of information and controls such that
the information becomes the affordance
through which the user (or automaton)
obtains choices and selects actions.
— Roy T. Fielding

11. Hypertext [is] the simultaneous presentation
of information and controls such that
the information becomes the affordance
through which the user (or automaton)
obtains choices and selects actions.
— Roy T. Fielding

12. Hypertext [is] the simultaneous presentation
of information and controls such that
the information becomes the affordance
through which the user (or automaton)
obtains choices and selects actions.
— Roy T. Fielding

13. A handle affords opening a door.
The handle is an affordance
through which you can open the door.

14. …the information becomes the affordance…

15. Hypertext [is] the simultaneous presentation
of information and controls such that
the information becomes the affordance
through which the user (or automaton)
obtains choices and selects actions.
— Roy T. Fielding

16. Hypertext [is] the simultaneous presentation
of information and controls such that
the information becomes the affordance
through which the user (or automaton)
obtains choices and selects actions.
— Roy T. Fielding

17. SC SC
RPC REST
1
2
3
SC
SC
SC
SC

18. SC
REST
SC
SC
Loose conversational coupling
Enabling clients to discover
at runtime how to correctly
interact with a service is
a loosely coupled design practice
— Cesare Pautasso & Erik Wilde

19. SC
REST
SC
SC
The server has to provide
the affordance towards
next steps the client can take.
It is impossible
for the server to know all steps
any client might want to take.
Tight affordance coupling

20. SC
SC SC SC
closed world open world open world
“today’s weather in Rio”
“tomorrow’s weather in Rio” “plane tickets to Rio” “hotels in Rio”
Weather API

21. Distributed Affordance
An Open-World Assumption
for Hypermedia
Problem statement
Concept and Architecture
Demo

22. C
P
S
user
publisher
provider
distributed
affordance

23. S
Publishers offer representations
that contain semantic annotations.
HTML
&
Microdata

24. Providers offer semantic descriptions
of the actions they support.
RESTdescP

25. Based on the semantic annotations,
matching service descriptions are instantiated.
P
P
P
HTML
&
Microdata
+ =

26. Based on the semantic annotations,
matching service descriptions are instantiated.
+ =Rio
Rio
Rio

27. Based on the semantic annotations,
matching service descriptions are instantiated.
Rio
Rio

28. * 1
*
1
Representation RepresentationEnricher
«use»
ResourceExtractor
«use»
Resource
«instantiate»
APICatalogAPIDescription
«instantiate»
PreferenceManager
ActionGeneratorAction
«instantiate»
«use»
Figure 1: The resources inside a representation are extracted 1 and combined with api d
based on the user’s preferences 3 , into actions 4 , for which affordances are added to the repr
4. ARCHITECTURE
4.1 Components
the role of the PreferenceManager can be
the APICatalog, which then only includes
that match the user’s preferences.

29. Distributed Affordance
An Open-World Assumption
for Hypermedia
Problem statement
Concept and Architecture
Demo

31. <div id="book" itemscope itemtype="http://schema.org/Book">
<span itemprop="name">The Catcher in the Rye</span> -
by <a itemprop="author" href="#salinger">J.D. Salinger</a>
<div itemprop="aggregateRating" itemscope>
<span itemprop="ratingValue">4</span> stars -
<span itemprop="reviewCount">3077</span> reviews
</div>
<div class="affordances" data-for="book">
<em>the browser will insert affordances here</em>
</div>
</div>

35. centralized affordance
distributed affordance
publisher-driven
mostly within application
user-driven
on the entire Web
tight
affordance coupling
loose
affordance coupling

36. Hypermedia as the engine of application state
only works to the extent by which the publisher
can predict what affordance the client needs.
Distributed affordance uses semantic technologies
to generate the needed affordance at runtime.

37. Distributed
Affordance
An Open-World Assumption
for Hypermedia
@RubenVerborgh
distributedaffordance.org