This document proposes a RESTful approach to OGC web services. It discusses representing OGC services like WFS, WCS, and WPS in a RESTful manner using HTTP methods and URLs to represent resources and operations. Key points include: - Representing everything as URLs and exposing resources and attributes rather than functions and inputs/outputs. - Using standard formats like Atom Publishing Protocol and JSON for output rather than SOAP/WSDL. - Representing OGC services like WfCS (Workflow Chaining Service) in a RESTful way, with workflows, definitions, instances, activities etc. as resources that can be retrieved and modified via HTTP methods. - Starting workflow instances by POST

1. RESTful OGC Services
User-Centric Resource Oriented Architecture (ROA) Approach
Pat Cappelaere, pat@vightel.com
Linda Derezinski, linda@i-sol.biz
John Mettraux, john@openwfe.org
Keith Swenson, KSwenson@us.fujitsu.com
Andrew Turner, Mapufacture
Version 4
1
DRAFT Aug 13, 2007

2. OGC Services
SOAPful REST (Classic) RESTful
GetCapabilities
GetFeasibilities
GetObservation
DescribeTasking
Submit...
Mandatory
RPC/Hybrid
Option

3. Why?

4. GEO - GEOSS [G]EO-Web 2.0
Movie http://blog.geobliki.com

5. GEOSS Use-Case South Africa
Transmission Power Grid (Red)
[G]EO-Web 2.0

6. Fire Season
MODIS Fires (every 4 hours)
Population Overlay
Power Grid [G]EO-Web 2.0

7. Notify Me:
Subscription PowerLineThreat within 10km (6nm)
in my area of interest (BBOX) [G]EO-Web 2.0
use Twitter, IM and SMS

8. User Receives Alert
Alert PowerLineThreat within 10km (6nm)
in BBOX [G]EO-Web 2.0
use email, Twitter, IM and SMS
User clicks on url

9. Feed Publication / Aggregation [G]EO-Web 2.0

10. KML Feed Visualization in GE [G]EO-Web 2.0
Threat:
Fire at 3nm
lat=xxx
long=xxx
Do You Want to Image?

11. Custom Data Product To The DeskTop [G]EO-Web 2.0

12. Problem Statement [G]EO-Web 2.0
• Many National & International Organizations
• Scarce Resources
• Money
• Time
• Engineering Resources
• We Need All Of the OGC Services

13. Market Positioning
RESTful SOAPful
Web Services
Service Oriented Architecture
Market NO IT Infrastructure Big IT Infrastructure
Mass Market Corporate 100 America
Users Neo-Geographers Corporate Developers/Engineers
Capability 80% 100%
Cost 10% 100%
Time 10% 100%
Risk Low HIgh

14. Technical Differences
RESTful SOAPful
Everything is a URL
Expose Resources Expose Functions
and Attributes and Inputs/Outputs
WADL
Discovery APP service Document WSDL
Spec Size Very small if existent Very Large
Schemas non-existent extensive
Language Html / Javascript / Ruby Java, C++. .NET
Framework Ruby on-Rails EJB
Security OpenID/PKI, OpenAuth... WS-Security (Geo-DRM)

15. SOAP - WSDL ...
xsd wsdl
common 0.3.20 9
context 1 2
csw 2.0.2 6 6
ebxml-regrep 3 1
filter 1.2 4
gml 3.2 94
hma 0.95 5
ols 1.1 11
ows 1 9
phr 0.81 2
sld 1 1
swecommon 1.0.3 2
wcs 1.0.2 7
wfs 1.2 2 5
wms 1.3 3
wrs 1.0. 4
wsdl 4
xlink 1.0. 1
xml 2
Total 165 15

16. Unique Opportunity
For System-Level
Architectural Change

17. RESTful Services For ROA Everything is a url!
• http://www.oreilly.com/catalog/9780596529260/index.html
“to codify the folklore,
define what’s been left
undefined, and try to move
past the theological
arguments.”
HTTP with Five Operations: HEAD, GET, PUT, POST and DELETE
17

18. Other Technologies For Successful ROA
• Publishing Formats: GeoRSS/Atom, KML
• Atom Publishing Protocol (APP)
• GData
• OpenSearch
• Security

19. Resource URI Patterns and Nested Resources
• Resource Collections Are Plural
• GET /recipes Retrieve all available recipes
• GET /recipes/{id} Retrieve specific recipe by id
• GET /recipes/{name} Retrieve specific recipe by name
• Nested Collections (recipes have many ingredients)
• GET /recipes/{id}/ingredients/ Retrieve all available ingredients for that particular recipe
• GET /recipes/{id}/ingredients/{id} Retrieve specific ingredient for that particular recipe
• same as: GET /ingredients/{id | name} Retrieve specific ingredient by id or name
Note: Last 2 GET’s return the same data.
BUT first one keeps track of context. Try to backtrack the URL to see what you would get
19

20. APP: Atom Publishing Protocol Format draft-ietf-atompub-protocol-17.txt
• The Atom Publishing Protocol is an application-level protocol for publishing and
editing Web Resources using HTTP [RFC2616] and XML 1.0 [REC-xml]. The
protocol supports the creation of Web Resources and provides facilities for:
* Collections: Sets of Resources, which can be retrieved in whole or in part.
* Services: Discovery and description of Collections.
* Editing: Creating, editing, and deleting Resources.
Geo/Atom In - Geo/Atom Out
http://bitworking.org/projects/atom/draft-ietf-atompub-protocol-17.html

21. Google GData
• The Google data APIs (quot;GDataquot; for short) provide a simple standard protocol for
reading and writing data on the web.
• GData uses either of two standard XML-based syndication formats: Atom or RSS. It
also has a feed-publishing system that consists of the Atom publishing protocol plus
some extensions (using Atom's standard extension model) for handling queries
(including geoqueries)
• Items of type Products containing the terms digital and camera in the area of
San Francisco: digital camera [item type: products] [location: @quot;San
Francisco, CAquot; + 50mi]
snippets/-/products?bq=digital+camera+%5blocation:@%22San+Francisco,CA%22%2b50mi%
5d

22. OpenSearch http://www.opensearch.org
• OpenSearch 1.1
• OpenSearch description document
• Discoverable by Browser
• Geo Extension Draft

23. Security
• OpenID 2.0 + Auth or PKI
• OpenAuth (AOL)
• That’s another topic of discussion!

24. Goal
Consistent User Experience
Across All OGC Services

25. What OGC Services Are We Looking At?
• Workflow Chaining Service (WfCS)
• Sensor Planning Service (SPS)
• Web Processing Service (WPS)
• Web Coordinate Transfer Service (WCTS)
• Web Feature Service (WFS)
• Web Notification Service (WNS) or OGC Publish/Subscribe (OPS-B)
• Sensor Observation Service (SOS)
• WCS (Steven Keens, PCI) 25

26. WfCS
• It Is The Most Complex Service, Let’s Do It First
• It Requires Asynchronous Services
• Patterns Can Be Used For SPS, WPS And WCTS
• Similar Patterns Can Be Inferred For WFS & SOS
• It Can Use WNS Or OPS-B
26

27. WfMC Reference Model http://www.wfmc.org/
Workflow
Chaining Service
(WfCS)
XPDL 2.0:
Serialization
Mechanism for the
Business Process
Modeling Notation
(BPMN 1.0)
27

28. Workflow Interoperability
Real-time
Offline
Workflow
Model Workflow
GUI
Internal
Persistence Engines
Layer
Representation
Layer
BPEL
A
XPDL
P
OpenWFE
BPMN 1.0 2.0
I
SensorML
WfCS
Level 0 Level 1 Level 2
28

29. WfCS Resources
• Users Are Resources, OpenID is Their URI.
• Note: You Always Know Your User and Have Access to Her Profile Information
• Users Create Workflows.
• Each Workflow Can Have one or more Definitions (or version).
• A Workflow Definition Orchestrates Activities Handled By Participants
• A Specific Workflow Is Instantiated (or Launched).
• A Particular Instance Has Traces (history) Related To Its Various Activities (start/
end).
Think of a Workflow as a blueprint that goes through the versioning process as time goes by. A Workflow is a mere entry in a registry to maintain its name
consistent over time. The definitions are the modified versions of the flow as designed by the engineer and uploaded to the server.
These different versions can be enabled, disabled and eventually deleted.
Another to think of it is that a workflow is akin to a catalog entry with one or more definitions attached to it as different versions
29

30. WfCS Resources Are:
• Users
• Workflows
• Definitions
• Instances
• Activities
• Traces
• Participants

31. Discovery
• WADL
• APP Service Document
• http://geobpms.geobliki.com/wfcs/app

32. Web Application Description Document: WADL
https://wadl.dev.java.net/
http://weblogs.java.net/blog/mhadley/archive/2005/05/introducing_wad.html
GET /wfcs.wadl Returns the WADL document for workflow resource
REST Equivalent of OGC GetCapabilities
or WSDL
32

33. Resource Metadata
• HEAD /wfcs/workflows
• GET /wfcs/workflows.metadata
• GET /wfcs/instances.metadata
• GET /wfcs/definitions.metadata
See Google GData
33

34. Retrieving Workflows
• GET /wfcs/workflows Retrieve all available workflows
• GET /wfcs/workflows.atom Retrieve all available workflows in atom output
• GET /wfcs/workflows/11 Retrieve specific workflow by id
• GET /wfcs/workflows/get_sa_threats Retrieve specific workflow by name
34

35. Threat Generation Flowchart
Acquire
MODIS
Generate
Polyons
EO-1
SPS
Generate
Threats
ASTER
SPS
Get
Feasibilities
SPOT-5
SPS
Get
Cloud
Coverage
Publish
WFS-B
Threats

36. BPMN Workflow

37. Workflow Definitions
• Uses XPDL 2.0 [generated from an external GUI]
• GET /wfcs/workflows/get_sa_threats/definitions
• GET /wfcs/workflows/get_sa_threats/definitions/v1_0
• To create/upload a new definition to be versioned:
• POST /wfcs/workflows/get_sa_threats/definitions
With XML Payload
37

38. Starting Workflow Instance
POST /wfcs/workflows/get_sa_threats/instances Launch specific workflow by name, and use latest enabled version
<entry xmlns:g='...' xmlns='http://www.w3.org/2005/Atom'>
<title>Get SA Fire Threats</title>
<category term='sa,fire,threats' scheme='http://geopbms/1.0'/>
<content>Get South African Fire Threats workflow</content>
<g:item_type>instances</g:item_type>
<g:command>start</g:command>
<g:context_data>
<scenario>2</scenario>
<all_threats>data/sa_all_threats.kml</all_threats>
<final_threats>data/sa_final_threats.kml</final_threats>
<feed_file>data/sa_threat_feed_file.xml</feed_file>
<send_to_draper>0</send_to_draper>
</g:context_data>
</entry>
Instance Location is returned 38

39. Dealing With Workflow Instances
• GET /wfcs/instances.atom
• Returns Atom Feed
• Returns Instance Attributes, Status, ContextData and ResultData
<entry>
<title>Get SA Fire Threats</title>
<link href=quot;http://geobliki.com/wfcs/instances/294quot; rel=quot;editquot;/>
<link href=quot;http://geobliki.com/wfcs/definitions/11quot; rel=quot;alternatequot;/>
<id>http://geobliki.com/wfcs/instances/294</id>
<created>2007-09-12T14:15:55Z</created>
<updated>2007-09-12T14:15:55Z</updated>
<author>
<name>cappelaere</name>
</author>
<content>Get South African Fire Threats workflow</content>
<g:item_type>instances</g:item_type>
<g:command>start now</g:command>
<g:status>scheduled</g:status>
<g:context_data>
<feed_file>data/sa_threat_feed_file.xml</feed_file>
<send_to_draper>0</send_to_draper>
<all_threats>data/sa_all_threats.kml</all_threats>
<final_threats>data/sa_final_threats.kml</final_threats>
<scenario>2</scenario>
</g:context_data>
<g:result_data>
</g:result_data>
<g:traces>
</g:traces>
</entry>
39

40. Modifying Workflow Instances
• PUT /wfcs/instances/294
<entry xmlns:g='http://geopbms/1.0' xmlns='http://www.w3.org/2005/Atom'>
<g:command>terminate</g:command>
</entry
• PUT /wfcs/instances/294
<entry xmlns:g='http://geopbms/1.0' xmlns='http://www.w3.org/2005/Atom'>
<g:command>suspend</g:command>
</entry
• PUT /wfcs/instances/294
<entry xmlns:g='http://geopbms/1.0' xmlns='http://www.w3.org/2005/Atom'>
<g:command>resume</g:command>
</entry
40

41. Sensor Planning Service (SPS) -- Old Way
• User can submit a task request and get an ID back
• Submit
• User can get status information about that task and change some task attributes
• GetStatus, UpdateRequest
• User can cancel request
• CancelRequest
• Service allows users to get access to files generated as a result of the task
• DescribeAccess
• Service allows users to check feasibilities
• GetFeasibility
41

42. RESTful SPS
• POST /wfcs/workflows/eo1-tasking/instances Creates new task, input parameters
are defined in definition file
• <entry>...</entry>
• GET /wfcs/instances/24.atom
Retrieves Task Instance Information
(status and result data if available)
• PUT /wfcs/instances/24.atom
Updates Task Instance Information
• <entry>..</entry>
• DELETE /wfcs/instances/24.atom Cancels Task Instance
• POST /wfcs/workflows/eo1-feasibility/instances Submits a GetFeasility Request
• <entry>...</entry>
Rerieves the GetFeasility Response
• GET /wfcs/workflows/instances/25.atom in result_data
42

43. RESTful SPS - Page 2
• DescribeTasking
• GET /wfcs/workflows/eo1-tasking
• DescribeFeasibility Retrieves XPDL for EO-1 Tasking
• GET /wfcs/workflows/eo1-feasibility Retrieves XPDL for EO-1 GetFeasibility
43

44. WPS & WCTS
• They are processes which map directly to named workflows
44

45. WFS Page-1
• RESOURCES ARE THE FEATURES
• GET /wfs/app Retrieves WFS APP Service Document
• GET /wfs/{feature}.atom Generates an atom feed with all features of that type
• GET /wfs/{feature}.metadata Generates Metadata document for that feature type
45

46. WFS with Transactions (WFS-T) Page 2
• POST /wfs/{feature}
XML Payload: <entry>...</entry>
• PUT /wfs/{feature}/{id}
XML Payload <entry>...</entry>
• DELETE /wfs/{feature}/{id}
46

47. WFS Filter Page-3
• Uses OpenSearch
• Keywords
• BBOX
• Timespan queries
• Create Your Custom OpenSearch Template
• Browser will discover it automatically
47

48. WNS / OPS-B
• Web Notification Service / OGC Publish/Subscribe
• Receives Atom Feeds
• Matches entries with user-based subscriptions
• Delivers custom feed using user-selected notification preferences

49. Resource Notification Service
• Every Resource Has An URI That Follows A Simple Pattern
• When A Resource Operation Takes Place, An Event Is Generated For That
URI
• You Can Subscribe For Those Events
• For That Specific Resource
• For That Specific Collection
49

50. Subscriptions
POST /wns/subscriptions To create a new subscription
Examples
POST /wns/subscriptions Subscribe to all workflow events (CRUD)
<path>uri</path>
Subscribe to specific workflow event by name
uri = /wfcs/workflows/eo1-tasking
Subscribe to all workflow definitions events (CRUD)
uri = /wfcs/definitions/*
uri = /wfcs/instances/* Subscribe to all workflow Instances events (CRUD)
uri = /wfcs/instances/*/traces/* Subscribe to specific workflow instance trace events
use DELETE to unsubscribe 50

51. Notifications
POST /wns/notifications
<email_address>pat@cappelaere.com</email_address>
<im_address>cappelaere@gmail.com</im_address>
<twitter_address>cappelaere</twitter_address>
PUT /wns/notifications
<email>disabled | enabled</email>
<im>disabled | enabled</im>
<twitter>disabled | enabled</twitter>
<notifications>enabled | disabled </notifications>
51

52. Sensor Observation Service (SOS)
• GET /sos/app
• Sensor Collection
• GET /sos/sensors/ Retrieve all available sensors (html)
• GET /sos/sensors.atom Retrieve all sensors in atom format
• GET /sos/sensors/{id|name} Retrieve specific sensor by id or name
• GET /sos/sensors/{id|name}.atom Retrieve specific sensor by id or name in atom format
52

53. SOS (cont)
• Getting Observations
• GET /sos/observations[.atom] Retrieve all observations html/atom
• GET /sos/observations.metadata Retrieve all observations metadata
• GET/sos/observations/{id|name}[.atom] Retrieve a specific observation by id or name html/atom
• GET /sos/observations/{id|name}.metadata Retrieve specific sensor by id or name in atom format
• GET /sos/observations/{id|name}/offering/{id|name}.{format}
Retrieve specific offering by id/name in a specific format (.tiff/.tar.gz/.jpg, etc)
• GET /sos/observations/{id|name}/offering/{id|name}.metadata
Retrieve specific offering by id/name meta data

54. SOS Search, Exactly like WFS’s Search
• Uses OpenSearch
• Keywords
• BBOX
• Timespan queries
• Create Your Custom OpenSearch Template
• Browser will discover it automatically

55. SOS-T
• PUT /sos/observations/{name}
XML Payload <xml>...</xml>
• PUT /sos/observations/{name}/offering/{name}
XML Payload <xml>...</xml>
• DELETE /sos/observations/{id|name}
• DELETE /sos/observations/{id|name}/offerings/{id|name}