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OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
OGC Capabilities Documents In The ROA
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OGC Capabilities Documents In The ROA

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This presentation shows that an OGC WMS Capabilities document is the representation of a resource even if it is the result of the operation of a software. Thus we should also treat it as a …

This presentation shows that an OGC WMS Capabilities document is the representation of a resource even if it is the result of the operation of a software. Thus we should also treat it as a *document*!

Lets start to think about how REST can be put to use in the geospatial context.

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  • 1. Hosted by Additional Sponsors: June 2008  TC Meeting: Architecture DWG Presentation  66th OGC Technical Committee   Potsdam, Germany Arnulf Christl June 02, 2008 Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved.
  • 2. Agenda • Scope of this presentation • RESTful OGC Web Services? • Introducing to the ROA (Resource Oriented Architecture) • OGC WMS in the ROA • Recap WMS Capabilities • Reading the Capabilities but not getting Maps • How to do Better: LegendURL • Making Capabilities findable Copyright: WhereGroup GmbH & Co. KG. Licensed under GNU FDL http://www.gnu.org/licenses/fdl.txt   and CreativeCommons 3.0 ShareAlike Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 2 Geographically
  • 3. Scope of this presentation • This presentation shows that an OGC WMS Capabilities  document is the representation of a resource (even if it is  the result of the operation of a software). • The idea is NOT to start a  discussion whether SOAP will  clean the REST of the web. • The idea is NOT to present REST  as the solution to all problems. • The idea is to start thinking about how REST can be put to use. Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 3 Geographically
  • 4. RESTful OGC Web Services? • According to Wikipedia OGC Services have been designed  around the REST paradigm [1]. • This is funny because 10 years ago the term REST and  RESTful  services was yet to be born. • Maybe the OGC was more avant­garde than we might  have expected?  • Probably the OGC design simply followed standard best  practices to serve the emerging WAN architecture. • As an example we look into the standard OGC WMS. [1] http://en.wikipedia.org/wiki/Open_Geospatial_Consortium Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 4 Geographically
  • 5. Introducing the ROA • The Resource Oriented Architecture is about enabling the  programmable web. It is the home for RESTful web  services. • Instead of calling remote procedures at one single address  it uses distributed resources across the web. • Many implementations of OGC WMS standards are based  on a software's perspective of the architecture. • The ROA is the architecture's perspective of a software that  runs as a service.  Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 5 Geographically
  • 6. The ROA Concepts and Properties Four concepts: Resources Their names (URL) Their representations The links between them  and four properties Addressability Statelessness Connectedness A uniform Interface From: RESTful Web Services, Richardson & Ruby, page 105 Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 6 Geographically
  • 7. OGC WMS in the ROA • The OGC WMS standard is not all that interesting from a  programmable web's perspective because it only returns  pretty but dumb images.  • But the OGC WMS Capabilities document is a good start to  look what could be done better • The Capabilities already contains (almost) everything that  is required to make clients get maps in the ROA.  • Clients must know how to formulate a GET request with  scoping parameters, some of which have explicit values. Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 7 Geographically
  • 8. The OGC WMS Capabilities Document • The OGC WMS capabilities document contains information  about "maps" (the resource) and how to access them (GET  a representation). • The Capabilities document is one possible representation  (the meta data) of the resource "maps". • It contains hints on how to GET (GetMap) more  representations (images) of the named resource (maps). • Although it contains redundant information about WHERE  the resource is, the client still must have implicit knowledge  of HOW to GET the representation. Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 8 Geographically
  • 9. Getting OGC WMS Capabilities [1] • OGC WMS capabilities documents have a location (URL) http://wms.oregonexplorer.info/ecwp/ecw_wms.dll? • Then the resource has to be scoped with a set of defined  parameters to actually get the document. ?REQUEST=GetCapabilties&SERVICE=WMS&VERSION=1.1.1 • This scoping information (in practice) never changes. http://wms.oregonexplorer.info/ecwp/capabilites ...would be just fine, maybe add the version of the service: http://wms111.oregonexplorer.info/ecwp/capabilites • The Capabilties document is just a representation of the  resource "maps" that exposes its meta data. [1] http://wms.oregonexplorer.info/ (OGC web site of the month 03/2008) Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 9 Geographically
  • 10. Reading the Capabilities Documents • The "Capabilities" contains information WHERE to get  <Request> <GetCapabilities> maps but not HOW to get them: <Format>application/vnd.ogc.wms_xml</Format> <DCPType> <HTTP> <Get> <OnlineResource xlink:href="http://wms.oregonexplorer.info/ecwp/ecw_wms.dll?"/> </Get> </HTTP> </DCPType> </GetCapabilities> <GetMap> <Format>image/png</Format> <Format>image/jpeg</Format> <DCPType> <HTTP> <Get> <OnlineResource xlink:href="http://wms.oregonexplorer.info/ecwp/ecw_wms.dll?"/> </Get> [...] Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 10 Geographically
  • 11. Not Getting the Map • To get a map representation of the OGC WMS resource  the client has to scope it with parameters. http://wms.oregonexplorer.info/ecwp/ecw_wms.dll?  REQUEST=GetMap SERVICE=WMS VERSION=1.1.1 LAYERS=2005ORTHOIMAGERY.ECW FORMAT=image/jpeg STYLES= BGCOLOR=0xFFFFFF TRANSPARENT=TRUE SRS=EPSG:4326 BBOX=­122.168515234362,42.8926048497946,­122.039660890008,42.9934387129544 WIDTH=835 HEIGHT=705 Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 11 Geographically
  • 12. Getting the Map • Some of these parameters are irrelevant, some should be  part of the URL, some I don't know what to do about either.  http://wms111.oregonexplorer.info/ecwp/ecw_map?  REQUEST=GetMap SERVICE=WMS VERSION=1.1.1 ? LAYERS=2005ORTHOIMAGERY.ECW FORMAT=image/jpeg STYLES= BGCOLOR=0xFFFFFF TRANSPARENT=TRUE ? SRS=EPSG:4326 BBOX=­122.168515234362,42.8926048497946,­122.039660890008,42.9934387129544 WIDTH=835 HEIGHT=705 Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 12 Geographically
  • 13. LegendURL does it better [1] • This OnlineResource has all the WHERE and the HOW: [...]     <Layer queryable="0" opaque="0" cascaded="0">         <Name>railroad_line</Name>         <Title>Railroad lines</Title>         <SRS>epsg:4326</SRS>         <LatLonBoundingBox minx="5.98259" miny="47.4064" maxx="15" maxy="54.9045" />         <BoundingBox SRS="EPSG:4326"                     minx="5.98259" miny="47.4064" maxx="15" maxy="54.9045" />         <Style>           <Name>default</Name>           <Title>default</Title>           <LegendURL width="20" height="10">              <Format>image/png</Format>              <OnlineResource xmlns:xlink="http://www.w3.org/1999/xlink" xlink:type="simple" xlink:                href="http://wms.wheregroup.com/cgi­bin/germany?version=1.1.1&service=WMS&                 amp;request=GetLegendGraphic&layer=railroad_line&format=image/png"/>           </LegendURL>         </Style>     </Layer> [1] http://wms.wheregroup.com/cgi­bin/germany [...] Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 13 Geographically
  • 14. Modifying Capabilities Documents • Capabilities with WHERE and HOW to get maps: <Request> <EPSG4326> <Format>image/png</Format> <Format>image/jpeg</Format> <DCPType> <HTTP> <Get> <OnlineResource xlink:href="http://wms.oregonexplorer.info/ecwp/4326/ecw_map?"/> </Get> </HTTP> </DCPType> </GetCapabilities> <EPSG:26910> <Format>image/png</Format> <Format>image/jpeg</Format> <DCPType> <HTTP> <Get> <OnlineResource xlink:href="http://wms.oregonexplorer.info/ecwp/26910/ecw_map?"/>  </Get> Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 14 Geographically
  • 15. The ROA Rules! Four concepts:  in              up  Resources capabilities  /   left  <[MAP]>  right Their names (URL) maps out           down      Their representations legends capabilities   Legend The links between them  ... and four properties Addressability Statelessness Connectedness A uniform Interface From: RESTful Web Services, Richardson & Ruby, page 105 Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 15 Geographically
  • 16. Making Capabilities Findable • Expose OGC WMS Capabilities documents as really  beautiful documents not as the result of a remotely  invoked operation of a software. • Give the Capabilities Document an extra home (URL).  • The Capabilities Document is the v­card of the service and  must contain all information that is needed to access the  resource and get a result.  • Explore how to use XHTML as a format that is readable by  machines and humans alike. Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 16 Geographically
  • 17. Discussion Thank you for your attention. Copyright: WhereGroup GmbH & Co. KG. Author: Arnulf Christl  This  presentation  is  dual  licensed  under  GNU  FDL  and  WhereGroup GmbH & Co. KG Creative Commons 3.0 Share Alike. Choose the one that fits  Siemensstr. 8 your needs best. The presentation master, first page and last  53121 Bonn page (this one) are what the GNU FDL refers to as invariant  Germany sections.  Please  do  not  modify  these  pages  without  getting  http://www.wheregroup.com/  written permission by the author. Find the full text of the GNU  FDL at: http://www.gnu.org/licenses/fdl.txt  Helping the World to Communicate Copyright © 2008, Open Geospatial Consortium, Inc., All Rights Reserved. 17 Geographically

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