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
