OGC Interoperability Day at Unidata:

Standards-based Web Services Interfaces to
Existing Atmospheric/Oceanographic Data Systems

Primary Issues at Unidata OGC Interoperability Day in September in Boulder

• Few implementations of WCS 1.1 and CS-W 1.0 to test for interoperability
• General, all-encompassing specifications become too complicated for specific data categories
  
• WCS 1.2 direction substantially different from WCS 1.1
• OGC specifications tending toward "core" and "extensions" approach, e.g.
  
  • WCS 1.2
  • GML
  • Architecture Board discussions
    
• Need for more focus on practical implementation and testing
• GALEON CF-netCDF realm needs
  • a more general data model
  • simpler interface specification with extension profiles for specific categories

Possible WCS Implementation and Experimentation Process

• Start with existing WCS 1.0 implementation
• Find limitations via interoperability experimentation
• Augment specs AND implementations to address limitations
• Feed results of implementation and experimentation into RWG

The idea behind this approach is to ground the interface process in practical implementation and experimentation to ensure that the resulting interface specifications are practical and can be used to distribute real data to existing clients in an interoperable fashion.  The ultimate objective is to feed the lessons learned from actual implementations and experimentation into the standards definition process. This will be particularly valuable in the "core plus extensions" specification environment where only a few new features would be added into the core, but experimentation with specific dataset categories might very well result in several practical, agreed-upon extensions serving specific communities.

Core Plus Extensions Approach to Specifications

• All encompassing but unwieldy GML
• WCS 1.2 heading that way
• OGC Architecture Board discussing issue in general

Strategic Objectives:

• Agreed-upon high-level dataset categories
• CF-netCDF conventions or extensions for those categories
• Explicit means of expressing CRS for each category
• Mapping of each category into ISO 19123 coverage specification
• Mechanism within WCS, WFS, SOS for delivering such coverages

High-level Dataset Categories

• Grids
• Points
• Station observations
• Trajectories
• Swaths
• Radar volumetric scans
• Irregular grids (as per coastal oceans modeling community)

Categorization Schemes:

Action Plan Outline

The steps required to achieve the long term vision for interoperability via standard interface specifications for common CF-netCDF datasets are as follows:

1. The CF-netCDF community comes to some agreement on the fundamental set of high-level dataset categories
   
2. Members of the CF-netCDF community define extensions to or profiles of the current CF conventions for each of the dataset categories. The result is that, over time, the community has well defined data models and clearly specified extensions for each of the categories.  A central issue that must be addressed in each case is defining explicit semantics (and perhaps syntax) for specifying spatial location information.  The CF community will have to address the difficult issues relating to CRS (Coordinate Reference System) definitions used in the formal georeferencing standards community.
   
3. Community members with expertise in ISO coverages, map the data model for each CF-netCDF extension into the ISO 19123 coverages model.  The result of this effort is that each dataset category is mapped directly to an ISO standard coverage type.  The standards community may have to extend some of their approaches to allow for what amounts to  "parameterized" versions of the EPSG specs.
   
4. Determine whether and how each CF-netCDF extension and the corresponding ISO coverage type:
   
   
   • can be expressed as Scientific Feature Types in GML and
   • relates to the Sampling Feature Types of the OGC Observations and Measurements
     
5. Determine whether and how each coverage type can be delivered via standard service protocols, e.g.:
   
   
   • as features in GML (with binary encodings??) via WFS
   • as sampling features via SOS
   • as coverages via WCS

Laid out like this, there is clearly a lot of work to be done.  However, it needn't be overwhelming because it lends itself to decomposition into tasks that can be undertaken in parallel with different communities of expertise working on their components with a manageable amount of coordination with others.  In particular, efforts are already underway to establish CF extensions for station observations.  The coastal oceans community has begun a similar effort for the "irregular grids" used in their models.  Efforts are in place to map the current CF conventions for grids into the ISO 19123 coverage model.

Action Plan Details

The revised action plan is being fleshed out by the participating groups in another document at:
http://galeon-wcs.jot.com/WikiHome/GALEON%20Phase2%20Main%20Page/Revised%20GALEON%202%20Action%20Plan