Proposal to improve AIXM Temporality

Find the latest AIXM Temporality document on the AIXM website:

Clarify omitted correction numbers for non-SNAPSHOT time slices

Related AIXM CCB Issue:

The "AIXM Temporality 1.0" is not very clear about correction numbers. It assumes that every non-SNAPSHOT time slice has a sequenceNumber and correctionNumber, but in the examples, the correctionNumber is often obmitted. There may be an implicit convention that a missing correctionNumber means "correctionNumber=0", but this is nowhere explicitly stated.

So this convention correctionNumber=0 should be stated explicitly.

In addition, we propose to add a business rule ("best practice") which requires an explicit correctionNumber for all non-SNAPSHOT time slices. If there is an agreement, this "best practice" should also be stated in the AIXM Temporality document. In that case, the following XSLT script should be run over the Donlon test data:
<xsl:stylesheet xmlns:aixm="" xmlns:xsl="" version="1.0">
  <xsl:output method="xml"/>
  <xsl:template match="aixm:sequenceNumber[../aixm:interpretation!='SNAPSHOT' and not(../aixm:correctionNumber)]">
    <xsl:copy-of select="."/>
  <xsl:template match="@*|node()">
      <xsl:apply-templates select="@*|node()"/>

Clarify featureLifeTime property for SNAPSHOTs

The document doesn't clearly say whether a SNAPSHOT contains the featureLifeTime property or not. Assuming it does contain the featureLifeTime: How is it defined? Applying the same rules as for other properties, this would be the featureLifeTime at this point in time. On the other hand, it would make a lot of sense if the featureLifeTime was the full featureLifeTime (if it is known).

This is an important detail for implementing the WFS Temporality Extension.

For example, consider a feature with 3 BASELINEs and a lifespan over 3 months:
  • interpretation = BASELINE, validTime = [2014-01-01,2014-02-01), featureLifeTime = [2014-01-01,indeterminate)
  • interpretation = BASELINE, validTime = [2014-02-01,2014-03-01), featureLifeTime = [2014-01-01,indeterminate)
  • interpretation = BASELINE, validTime = [2014-03-01,2014-04-01), featureLifeTime = [2014-01-01,2014-04-01)

(sequenceNumber and correctionNumber omitted for brevity, no TEMPDELTAs)

How would the SNAPSHOT for 2014-02-15 look like?
  • A: interpretation = BASELINE, validTime = [2014-02-15], no featureLifeTime
  • B: interpretation = BASELINE, validTime = [2014-02-15], featureLifeTime = [2014-01-01,indeterminate)
  • C: interpretation = BASELINE, validTime = [2014-02-15], featureLifeTime = [2014-01-01,2014-04-01)

For every version there are good arguments: A means that the featureLifeTime is out of scope for SNAPSHOTs. B means that featureLifeTime is handled like any other property. C means that since we know the total featureLifeTime, we should also state it in the SNAPSHOT.
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Topic revision: r6 - 10 Sep 2014, MatthiasPohl

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