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65
Event an additional Event for correcting the geometry is being created. The corrected geometry now matches the filter criteria of the client’s subscription but the client cannot
resolve the reference to the former published ad-hoc airspace feature. Although this situation presumably is a rare case the issue should be discussed and a feasible solution
needs to be developed within the Event Architecture as the issue can affect security.
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10 Lessons Learned
10.1 AIXM Temporality Model
10.1.1 Clarify Snapshot Definition 10.1.1.1 Problem Statement and Description
Section 2.5 of the Temporality Model defines a Snapshot as follows: “SNAPSHOT = A kind of Time Slice that describes the state of a feature at a time instant,
as result of combining the actual BASELINE Time Slice effective at that time instant with all TEMPDELTA Time Slices that are effective at that time instant.”
This definition does not mention Permdeltas. Section 2.6 of the Temporality Model states the following:
“From a conceptual point of view, a PERMDELTA Time Slice occurs at the edge between any two consecutive BASELINE Time Slices and it contains values strictly for the
changed properties. [...] Conceptually, there exists a direct dependence between PERMDELTA and BASELINE Time Slices. However, this does not mean that the
BASELINE Time Slice needs to be effectively instantiated after each PERMDELTA. In an implementation, it is possible, for example, to “accumulate” PERMDELTA Time Slices.
The instantiation of a new BASELINE might occur, for example, after each third PERMDELTA affecting a feature.”
Apparently, the Temporality Model allows the static property values given in a Baseline to be superseded by changes introduced through Permdeltas, also during the validTime of
the Baseline.
Consider the following figure.
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Figure 24 – Snapshot with Baseline and Tempdelta
The figure shows a Snapshot that takes into account property values as defined by both a Baseline and a Tempdelta timeslice. The current Snapshot definition of the Temporality
Model covers this situation. Now consider the next figure.
