How to generate a KML with nested attributes and attributes with cardinality greater than one - kml

Question

I have a set of events that I want to export to KML. Those events have nested attributes and attributes with cardinality greater than one (maxOccur > 1).
Here is an example of one event presented as JSON:
{
"id": 1,
"date": "2018-01-01",
"client": {
"name": "Brad",
"since": "2017-12-01"
},
"products": [
{
"name": "P1",
"quantity": 20
},
{
"name": "P2",
"quantity": 40
},
]
}
One option that we are considering is use an arbitrary XML at ExtendedData. This option sounds good for Machine-to-Machine data interchange, but not for human read, because the Google Earth does not show those data very well in balloons:
<ExtendedData>
<id>1</id>
<date>2018-01-01</date>
<client>
<name>Brad</name>
<since>2017-12-01</since>
</client>
<products>
<product>
<name>P1</name>
<quantity>20</quantity>
</product>
<product>
<name>P2</name>
<quantity>40</quantity>
</product>
</products>
</ExtendedData>
Other option that we are considering is use Schema + SchemaData + BallonStyle, but the cardinality and nested attributes are not supported...
<Schema name="myEvent" id="myEvent">
<SimpleField type="int" name="id">
<displayName>Event id</displayName>
</SimpleField>
<SimpleField type="string" name="date">
<displayName>Event date</displayName>
</SimpleField>
<!-- workaround to nested data -->
<SimpleField type="string" name="clientName">
<displayName>Client name</displayName>
</SimpleField>
<SimpleField type="string" name="clientSince">
<displayName>Client since</displayName>
</SimpleField>
<!-- no idea how present attributes with more than one occurrence -->
</Schema>
There is another option that we should consider?

Answer 1

Data and SimpleData elements in KML ExtendedData are limited to name/value pairs with values as text but custom XML is allowed using a different namespace.
You can add arbitrary XML data to a Feature in KML from a non-KML XML namespace like Dublin core, RDF, or your own namespace. Here is a related tutorial.
Here's an example with arbitrary Dublin core XML in KML:
<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
<Document>
<name>ExtendedData Test with Dublin core XML</name>
<Placemark>
<name>Test data</name>
<ExtendedData xmlns:ns="http://example.org/myapp/">
<ns:metadata xmlns:dc="http://purl.org/dc/elements/1.1/">
<dc:description>
KML features a rich mix of
metadata information and services for the XML community.
</dc:description>
<dc:subject>XML, RDF, metadata, information
syndication services</dc:subject>
<dc:identifier>http://earth.google.com</dc:identifier>
<dc:language>en-us</dc:language>
<dc:date>2000-10-13</dc:date>
<dc:rights>Copyright 2000, O'Reilly Network</dc:rights>
<dc:publisher>O'Reilly and Associates, Inc.</dc:publisher>
</ns:metadata>
</ExtendedData>
<Point>
<coordinates>-71.7571,42.953</coordinates>
</Point>
</Placemark>
</Document>
</kml>
With your own namespace, you can store whatever XML you want with whatever nesting.
<Placemark>
<name>Test data</name>
<ExtendedData>
<data xmlns="urn:my.org:data">
<id>1</id>
<date>2018-01-01</date>
<client>
<name>Brad</name>
<since>2017-12-01</since>
</client>
<products>
<product>
<name>P1</name>
<quantity>20</quantity>
</product>
<product>
<name>P2</name>
<quantity>40</quantity>
</product>
</products>
</data>
</ExtendedData>
</Placemark>
Note however that this approach passes along the data within the KML for a machine-to-machine exchange since Google Earth does not process nor display this type of data. A third party application could take advantage of this type of XML data contained within the KML.
If you want at least part of the data to be human-readable via Google Earth, consider a hybrid solution with name-value pairs in Data/value elements for the simple values and a custom XML element for the more complex nested XML data.
<Placemark>
<name>Test data</name>
<ExtendedData>
<Data name="id">
<value>123</value>
</Data>
<Data name="date">
<value>2018-01-01</value>
</Data>
<customData xmlns="urn:custom">
<client>
<name>Brad</name>
<since>2017-12-01</since>
</client>
</customData>
</ExtendedData>
<Point>
<coordinates>-71.7571,42.953</coordinates>
</Point>
</Placemark>