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Introduction to the WXXS (XML Schema)

What is the WXXS?

The WXXM is the component of the Meteorological Information Exchange used for system-to-system exchange of meteorological information.

The Schema derives from the WXXM by mapping its features, attributes and business rules into XML.

WXXS is implemented as a Geography Mark-up Language (GML) application schema, conforming to version 3.2.1 of the GML specification. By conforming to the GML Specification, it is intended that the WXXS datasets will be compatible with third-party GML-compliant applications, and hence enable aeronautical users to reap the benefits of open Geographic Information Systems (GIS) standards.
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ICAO Annex 3 METAR Example

The example shown represents a simple METAR report, containing weather information relevant to an Aerodrome. The mandatory METAR properties, along with a number of optional properties (sea weather) are return in the observation result, encased in a avwx:AerodromeWx object.

Text-based report types include a rawText element that can be optionally used as shown to provide the original text-based METAR report. This is anticipated to be useful during the period of transition from plain text to more self-describing formats.

Since reports can be comprised of multiple observations and forecasts, each referring to a common featureOfInterest, the base report type includes an appliesTo property, which can be used to reference a 'master feature of interest' for the entire report.

As shown in the example, the featureOfInterest for each individual observation and/or forecast in the report may then reference the common feature of interest defined using the appliesTo property. Document-local references such as these, supported by the gml:id attribute, are a common pattern used in GML schema instances to represent complex objects efficiently in XML.
Untitled Document
< avwx:METAR
xmlns:avwx ="http :// www.eurocontrol.int / avwx /1.1"
xmlns:wx ="http :// www.eurocontrol.int / wx /1.1"
xmlns:wxont ="http :// wmo.int / ontologies / wx.owl #"
xmlns:om ="http ://www.opengis.net/om/1.0/gml32"
xmlns:gml ="http ://www.opengis.net/gml/3.2"
xmlns:xlink ="http ://www.w3.org/1999/ xlink "
xmlns:xsi ="http ://www.w3.org/2001/ XMLSchema-instance "
gml:id ="id0">
< avwx:rawText >
METAR KTTN 051853Z 04011KT 1/2SM VCTS SN FZFG BKN003 OVC010 M02/M02
A3006 RMK AO2 TSB40 SLP176 P0002 T10171017=
</ avwx:rawText >
Aerodrome weather observation.
< avwx:aerodromeWxObservation >
< wx:Observation gml:id ="id6">
< om:samplingTime >
< gml:TimeInstant gml:id ="id8">
< gml:timePosition >2008-11-04T12:00:00Z</ gml:timePosition >
</ gml:TimeInstant >
</ om:samplingTime >
< om:procedure xlink:href ="urn:fdc:faa.gov:Sensor:WeatherStation:01234"/>
<!-- Observed property links to higher-level Ontology concept that
corresponds to result type
< om:observedProperty xlink:href="http://www.eurocontrol.int/ont/avwx/1.1/wx.owl#AerodromeWx"/>
<!-- Feature of interest links to Aerodrome feature within this
METAR instance.
< om:featureOfInterest xlink:href ="#id2"/>
<!-- Result contains weather properties relevant to Aerodrome area of
< om:result >
< avwx:AerodromeWx gml:id ="id10">
< avwx:airPressure uom =" mBar ">900</ avwx:airPressure >
< avwx:airTemperature uom ="C">30</ avwx:airTemperature >
< avwx:dewpointTemperature uom ="C">20</ avwx:dewpointTemperature >
< avwx:verticalVisibility uom ="NM">2</ avwx:verticalVisibility >
< avwx:windDirection uom ="deg">30</ avwx:windDirection >
< avwx:horizontalVisibility gml:id ="hv1">
< avwx:minimumVisibility uom ="NM">5</ avwx:minimumVisibility >
< avwx:directionMinimum >NW</ avwx:directionMinimum >
</ avwx:horizontalVisibility >
< avwx:windSpeed uom =" kt ">15</ avwx:windSpeed >
< avwx:qnh uom =" mBar ">900</ avwx:qnh >
< avwx:qfe uom =" mBar ">900</ avwx:qfe >
< avwx:cloudCondition gml:id ="cc1">
< wx:base uom =" ft ">2000</ wx:base >
< wx:cloudType >CUMULUS</ wx:cloudType >
</ avwx:cloudCondition >
< avwx:cloudCondition gml:id ="cc2">
< wx:base uom =" ft ">15000</ wx:base >
< wx:cloudType >CIRRUS</ wx:cloudType >
</ avwx:cloudCondition >
< avwx:seaWx >
< avwx:SeaWx gml:id ="id18">
< avwx:surfaceTemperature uom ="C">20</ avwx:surfaceTemperature >
< avwx:seaState > CALM RIPPLED</ avwx:seaState >
</ avwx:SeaWx >
</ avwx:seaWx >
</ avwx:AerodromeWx >
</ om:result >
</ wx:Observation >
</ avwx:aerodromeWxObservation >
Aerodrome is specified outside the context of individual observations
and forecasts within METAR report and referenced within each
observation/forecast to reduce redundancy in report instances.
< avwx:appliesTo >
< avwx:Aerodrome gml:id ="id2">
< gml:identifier codeSpace =" urn:icao:code:Aerodrome :">DEN</ gml:identifier >
< gml:name >BOS</ gml:name >
< gml:location >
< gml:Point srsName ="urn:ogc:crs:EPSG:4979" srsDimension ="3" gml:id ="id4">
< gml:pos >40.0 -70.0 1000.0</ gml:pos >
</ gml:Point >
</ gml:location >
</ avwx:Aerodrome >
</ avwx:appliesTo >
< avwx:stationId codeSpace =" urn:icao:code:weatherStation :">KDEN</ avwx:stationId >
< avwx:automated >true</ avwx:automated >
< avwx:missing >false </ avwx:missing >
</ avwx:METAR >

What the WXXS Doesn't Do

As can be quickly appreciated, the WXXS is large and complex. However, it should be remembered that it will be used in automated processes to make sure that diverse systems can communicate correctly. The XML will never be used directly by pilots, MET staff or other humans. Instead, the end user will see applications that apply appropriate Human Machine Interface (HMI) principles to present the XML encoded data.

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