[Requests] Comment to SOS 2.0 (OGC 10-037) from GWIE

Boisvert, Eric Eric.Boisvert at RNCan-NRCan.gc.ca
Tue Nov 30 06:33:48 EST 2010

Part A to be completed once.  Iterate Part B as needed.


1. Evaluator:
        Eric Boisvert (on behalf of the GWIE)
 Geological Survey of Canada
 eboisver at nrcan.gc.ca
 +01 418 654-3705

2. Submission: OGC® SOS 2.0 Interface Standard, OGC 10-037, 2010-09-02



1. Requirement: General

2. Implementation Specification Section number: General

3. Criticality: Minor

4. Comments/justifications for changes: [Comments]

In dealing with large datasets behind the SOS, clients (especially browser clients) can be overwhelmed by the sheer size of the results returned. WFS 1.0 provides a means to limit the number of features returned from a GetFeature request via the @maxFeatures attribute.  We feel this is easy to implement and worth emulating in SOS. This feature, combined with a sorting instruction, could also solve the problem of getting the latest value of a result.  Because the latest value in a time series cannot be expressed as a temporal request per se, being able to retrieve the first item of a sorted series could fill this gap.

Proposed Solution

We propose that SOS GetObservation, GetObservationByID and GetFeatureOfInterest add support for maxObservations, maxResults, and maxFeatures, to limit the number of observations and the number of elements of a complex result.  We also propose that parameters be added to control the sorting order of either/or observations and result elements.  The query semantics should be able to control observation limits and order independently of the results.  The semantics of these parameters are to be defined by the SOS SWG or by any other interested party.

These changes will enable the extraction of the latest Observation from a SOS as follows (parameter names are not official proposals here, but are examples to demonstrate the concept):

GetObservation sortBy="phenomenonTime" sortOrder="DESC" maxObservation="1"

It would also be possible to get the latest element of a time series in a result by performing a similar request

GetObservation result sorted by "time" result sort Order = "DESC" maxResults = "1"



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