Copyright © 2014 Open Geospatial Consortium
31
A B C D E F B D G H I B J G K L K A B C D EM N D GO P N Q
GP FR
to
A B C D EM N D GO P N Q
GP FR
If no time slice matches the filter, technically a schema-invalid document has to be returned. To avoid this, the service shall place a dummy time slice in the affected
features as defined in 8.1.1.
Example: see A.4, A.5, A.6, A.7, B.8.
9.2.2 Requirement: reqtime-slice-projectionrelevant-time
The optional relevantTime element serves as a shortcut to an otherwise lengthy check on the validTime property of the time slices. If it is present, only time slices that are relevant
for not before and not after a given time period or time instant shall be kept in the result, i.e. all time slices that define the state for that time.
Example: see A.3, A.4.
9.2.3 Requirements: reqtime-slice-projectioninclude-corrected and reqtime-slice-
projectioninclude-canceled
By default, canceled and corrected time slices, as defined in 5.3, are not part of the returned set of time slices. This can be changed by setting the properties
includeCanceled and includeCorrected to true, respectively. In the special case of setting includeCorrected to true, and setting includeCanceled to false, canceled time
slices shall not be returned.
Example: see A.7.
9.3 Requirements Class: WFS-TE Snapshot Generation
Requirements Class
http:www.opengis.netspecwfs-te1.0reqsnapshot-generation
Target Type Service
Dependency WFS-TE Core
Requirement reqsnapshot-generationcapability
List the identifier of the corresponding conformance class of this requirements class as an ows:Profile element in the ServiceIdentification
section of the Capabilities document. See also 10.
Requirement reqsnapshot-generationtime-instant
32
Copyright © 2014 Open Geospatial Consortium
Support the SnapshotGeneration clause for time instants Requirement
reqsnapshot-generationtime-period Support the SnapshotGeneration clause for time periods
Requirement reqsnapshot-generationevaluate-schedules
Raise an ‘OptionNotSupported’ exception if the evaluateSchedules attribute is set to true unless redefined
Figure 6: UML class diagram for SnapshotGeneration
The SnapshotGeneration class is a transformation clause that generates snapshot time slices according to AIXM-TM for the selected features. If this projection clause is present
in a request, time slices with SNAPSHOT interpretation are generated for the selected features for the given time. They replace the list history of time slices.
The optional property evaluateSchedules triggers the evaluation of properties with schedule for the given time. That means that the collection of properties is replaced by a
single property that contains the values valid at the given time see A.9 for an example. Schedule evaluation for time periods requires the service to drill down into the details of
each schedule.
As stated in 9.1.1, projection clauses are applied before transformation clauses. If a TimeSliceProjection is combined with SnapshotGeneration, this allows what-if-queries
like ‘what would be the current state or the state at time X of the feature if time slice Y was not among the history of time slices?’. However, this flexibility comes at a price:
with time slice filters in place, the history of time slices may become incomplete or even invalid e.g. when regarding inter-feature references and associations. It is up to the
client to formulate meaningful queries. The service is not required to perform a complete validation of the reduced time slice list and affected features. If it cannot produce a valid
state, it should produce an invalid snapshot as defined by the invalidSnapshot function in 9.3.1.
