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Notwithstanding the current interest in fully unifying the feature and coverage views (through the CRS generalization activity, for which the logical outcome is CRSþatureType), I believe that feature, coverage, observation, catalogue can already be seen as merely different views onto, projections of, or sections through, the underlying data soup. There now appears to be some agreement that a "feature" may have a property whose value varies in some way "across" the feature, for example in time or space (see sub-clause 6.5.3 and Figure 4 of Observations and Measurements - OGC 05-087r4 http://portal.opengeospatial.org/files/?artifact_id038) and that this value is a "Coverage" whose domain extent is the feature. In the proposed update to the SamplingFeatures clause (see OGC 07-002r1 http://portal.opengeospatial.org/files/?artifact_id 934&version=1) this is generalized further to allow variation with respect to non-spatial axes inherent to the "feature" (see sub-clause 7.1 and Figure 2). I've also been thinking about the implications of this model in terms of service composition: For example, if a feature type has a property with a coverage value, then a WFS "GetFeature" request for such a feature might use a GetCoverage request to a WCS "cascaded" behind the WFS in order to fully compose the response. There are some other similar interactions potentially implied by other SOS and specialised WFS operations. I had presented this in the form of what George Percivall calls "your horrible powerpoint picture" a couple of times in OGC forums mid last year (e.g. in the SWE WG at the Edinburgh TC). I think George's main problem was that my "SOS" pattern put a WFS and WCS behind the SOS, instead of vice-versa, which would match the idea of "observations" as being in some sense "more primitive" that features. However, I still stand by that analysis, and I have now added a couple of other variants, based on the "Sampling Feature Service" viewpoint, the "Domain Feature Service" viewpoint, and the "just the data" viewpoint. They are still in horrible PPT-ML, pending Bryan helping me figure out how to show it in UML, and definitely could use some refinement, but maybe time to share the ideas ... see attached. Simon
Attachment:
OGCInterfaces.ppt
Description: OGCInterfaces.ppt
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