OGC Xlink Policy and timeline to move to XLink 1.1

May 7, 2012

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Back in 2000, the OGC Members determined that the W3C XLink recommendation was well suited to the requirements for GML 2.0 as well as other OGC standards. However, at that time, W3C did not have a XLink schema. Therefore, the OGC Members decided to define an OGC XLink schema that was based on the W3C XLink recommendation. This XLink schema is now used in numerous OGC standards (See below).

Recently, the W3C finally published the XLink 1.1 schema. Further, a number of government procurement organizations have mandated the use of W3C XLink 1.1. Therefore, the OGC needs to transition from the OGC XLink 1.0 schemas to the W3C XLink 1.1 schemas. This sounds an easy enough transition. In reality, this is a major change and will break any application using OGC standards that reference XLink unless the application also transitions to the W3C XLink 1.1 schema.

At the 2011 Brussels meeting, the TC and the PC approved a motion that:

The OGC shall follow the XLink guidance as defined in the W3C XLink 1.1 recommendation: http://www.w3.org/TR/xlink11/

The motion further stated that 1.) all existing OGC standards that reference the OGC XLink shall be updated to reference the W3C XLink schema and 2.) that going forward any new standards work shall only reference the W3C XLink schema. At the same time, there is also a related XLink schema change so that simpleAttrs is used.


http://schemas.opengis.net/xlink/1.0.0/xlinks.xsd will be changed to http://www.w3.org/1999/xlink.xsd and

xlink:simpleLink will be changed to xlink: simpleAttrs )

The target date for implementing change is the weekend of July 21, 2012.

The process will be:

1. Scan schema repository for import of xlink to find a list of standards that use xlink.

2. Also scan for strings such as Gml:ReferenceType to find other possible places that xlink is required.

3. Whatever schema uses any of XLink schema components will need to replace the schema location. We need to do this for all schemas that import xlink. All these changes will be done to a copy of the existing OGC schema repository.

4. Create a copy of the OGC schema repository and announce this location so that product developers can test their implementations of affected OGC standards against this beta version of the OGC standards.

5. For software developers, they need to patch their products to use the revised OGC schemas.

6. Everyone will need to delete local copies, get a new copy from the OGC schema repository, and use the new schemas. There is also the possibility to use a tool such as the OASIS XML Catalogue to override the required change and to continue using the old XLink.

7. In July, we will then issue one global corrigendum for all the affected standards. Essentially, the current OGC schema repository will be replaced with the schemas that have been changed (and tested)The actual standards documents will not change – only the schemas. OGC policy is that the schemas are normative and that if there are differences between a standards document and a schema, then the schemas are normative.

Concurrently, we need aggressive OUTREACH, OUTREACH, OUTREACH to inform and educate the implementation and user community. For example, we need to:

  • Coordinate with TC 211
  • Coordinate with OASIS
  • Coordinate with the GeoSciML community
  • Coordinate with INSPIRE
  • Inform all technology developers that they need to check their offerings and determine what (if any) changes they need to make. Not just OGC Members but the whole community!
  • Coordinate with the Open Source community also
  • Use LinkedIn, Blogs, and other social media.

Below is a preliminary list of the OGC standards (and versions) impacted by this change

  • All versions of WM context
  • All versions of GML since version 2.0.0
  • All profiles of GML since 2.0.0
  • Image CRSs
  • All versions of OpenLS since version 1.1.0
  • All versions of OWS Common since 1.0.0
  • Symbology Encoding 1.0
  • All versions of SLD since 1.0.0
  • All versions of SensorML (including 2.0)
  • All versions of SWE Common
  • Table Join Service
  • All versions of Web Coverage Service
  • Web Feature Service 2.0
  • Web Map Service 1.3
  • WMTS
  • Web Processing Service

Reprinted with permission, Open Geospatial Consortium


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