46 Copyright © 2012 Open Geospatial Consortium.
the query language is less powerful the extension is less generic from a WFS perspective
7.3 Improvements for FES 2.0
7.3.1 Introduction of a new temporal filter or function: evaluateDuring
The AIXM 5 temporality model requires very specific handling to support all of it features. This makes it difficult to use a generic temporal filter that answers simple queries like: return
all airspaces that are currently active. One of the reasons for this is that time slices can overlap and override each other. Another reason is that an extensive timesheet system is used
to define recurring properties e.g. an airspace be active between sunrise and sunset on work days.
One solution for this would be the declaration of a custom filter function. This was already done in the SAA pilot, where an SLD was defined for an airspace based on its time to
activation. The complete filter for the evaluateDuring function,given below, is called with two arguments. The first argument simply specifies a filter that needs to be applied on AIXM
time slices, the second argument specifies the relevant time property. The function will return true if the first filter accepts a snapshot that can be generated during the time property
specified in the second argument. The second argument can specify either a period, or an instant.
ogc:Filter ogc:PropertyIsEqualTo matchCase=true
ogc:Function name=evaluateDuring ogc:Literal
ogc:Filter ogc:PropertyIsEqualTo matchCase=true
ogc:PropertyName xmlns:ns1=http:www.aixm.aeroschema5.1ns1:activationns1:AirspaceActi
vationns1:statusogc:PropertyName ogc:LiteralACTIVEogc:Literal
ogc:PropertyIsEqualTo ogc:Filter
ogc:Literal ogc:Literal
ns0:TimePeriod ns0:beginPosition2011-03-
30T15:59:51.003+02:00ns0:beginPosition ns0:endPosition2011-03-
30T19:58:51.003+02:00ns0:endPosition ns0:TimePeriod
ogc:Literal ogc:Function
ogc:Literaltrueogc:Literal ogc:PropertyIsEqualTo
ogc:Filter
Advantages
No extension schemas needed, the function only needs to be completely described to ensure that all implementations are the same.
The result of this query will contain the original time slices
The function is both very simple and generic
47 Copyright © 2012 Open Geospatial Consortium.
Disadvantages
Custom functions are not covered by the WFS spec, so needs to be defined elsewhere, generic clients will not be able to use it.
7.4 Improvements to AIXM 5.1
