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Hi all, I'm following on from previous conversations under the subject line "WCS CF-netCDF profile document", which was getting rather overloaded, largely my fault. It seems to be important to get a handle on what is a feature and what is a coverage. We've seen various viewpoints, so I thought I'd give my view based on a number of conversations that are slowly crystallizing in my head (thanks go to Andrew Woolf here). I think a "feature" is just a geographic "thing". The term is not meant to be discriminative - it's very closely analogous to an Object in Java, C++ or any number of other programming languages. It's simply a collection of attributes and methods (operations). A "Feature Type" is the definition of the feature, analogous to a Class in OO programming. A "coverage" is a data structure. It can be used to express the value of a particular attribute of a feature. For example, a Feature that expresses a timeseries of temperature at a point might have attributes encoding the geographic position of the measurement, plus all kinds of other metadata like the name of the station and so forth. The values themselves might be encoded as a coverage, which is the "value" attribute of the feature. (People who are familiar with CSML will recognise this model.) So the relationship is that a Feature "has a" Coverage. I think. ;-) Do others agree or have I got it wrong? So, if everything is a feature, then perhaps in future WFS will be the uber-specification that can serve everything? Well, maybe... I think things will get very (i.e. even more) complicated when we start thinking about how to subset the Coverage(s) that belong to a Feature, in the very general case. I can't quite grasp this myself yet. Do we embed a WCS-like subsetting query inside a WFS query? What does this mean for the future of WCS? Cheers, Jon -- Dr Jon Blower Technical Director, Reading e-Science Centre Environmental Systems Science Centre University of Reading Harry Pitt Building, 3 Earley Gate Reading RG6 6AL. UK Tel: +44 (0)118 378 5213 Fax: +44 (0)118 378 6413 j.d.blower@xxxxxxxxxxxxx http://www.nerc-essc.ac.uk/People/Staff/Blower_J.htm
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