GMLAS - Mapping examples

This page gives a few examples of how XML constructs are mapped to OGR layers and fields by the GMLAS - Geography Markup Language (GML) driven by application schemas driver.

Mapping examples

Schema

Document

OGR layers

Comments

 
<schema xmlns="http://www.w3.org/2001/XMLSchema">
<element name="MyFeature">
<complexType>
    <sequence>
        <element name="name" type="string"/>
    </sequence>
    <attribute name="id" type="ID" use="required"/>
    <attribute name="attr" type="string"/>
</complexType>
</element>
</schema>

<MyFeature id="my_id" attr="attr_value">
    <name>my_name</name>
</MyFeature>

Layer name: MyFeature
Geometry: None
id: String (0.0) NOT NULL
attr: String (0.0)
name: String (0.0) NOT NULL
OGRFeature(MyFeature):1
    id (String) = my_id
    attr (String) = attr_value
    name (String) = my_name

Element with attributes and sub-elements of simple type and maximum cardinality of 1.

 
<schema xmlns="http://www.w3.org/2001/XMLSchema">
<element name="MyFeature">
<complexType>
    <sequence>
        <element name="str_array" type="string"
                maxOccurs="2"/>
        <element name="dt_array" type="dateTime"
                maxOccurs="unbounded"/>
    </sequence>
    <attribute name="id" type="ID" use="required"/>
</complexType>
</element>
</schema>

<MyFeature id="my_id">
    <str_array>first string</str_array>
    <str_array>second string</str_array>
    <dt_array>2016-09-24T15:31:00Z</dt_array>
    <dt_array>2016-09-24T15:32:00Z</dt_array>
</MyFeature>

Layer name: MyFeature
Geometry: None
id: String (0.0) NOT NULL
str_array: StringList (0.0) NOT NULL
OGRFeature(MyFeature):1
    id (String) = my_id
    str_array (StringList) =
        (2:first string,second string)

Layer name: MyFeature_dt_array
Geometry: None
ogr_pkid: String (0.0) NOT NULL
parent_id: String (0.0) NOT NULL
value: DateTime (0.0)
OGRFeature(MyFeature_dt_array):1
    ogr_pkid (String) = my_id_dt_array_1
    parent_id (String) = my_id
    value (DateTime) = 2016/09/24 15:31:00+00

OGRFeature(MyFeature_dt_array):2
    ogr_pkid (String) = my_id_dt_array_2
    parent_id (String) = my_id
    value (DateTime) = 2016/09/24 15:32:00+00

Example with array and child layer

 
<schema xmlns="http://www.w3.org/2001/XMLSchema">
<element name="MyFeature">
<complexType>
    <sequence>
    <element name="identifier">
        <complexType>
        <sequence>
            <element name="name">
            <complexType>
                <simpleContent>
                <extension base="string">
                    <attribute name="lang"
                            type="string"/>
                </extension>
                </simpleContent>
            </complexType>
            </element>
            <element name="namespace" type="string"
                    minOccurs="0"/>
        </sequence>
        </complexType>
    </element>
    </sequence>
    <attribute name="id" type="ID" use="required"/>
</complexType>
</element>
</schema>

<MyFeature id="my_id">
    <identifier>
        <name lang="en">my_name</name>
        <namespace>baz</namespace>
    </identifier>
</MyFeature>

Layer name: MyFeature
Geometry: None
id: String (0.0) NOT NULL
identifier_name_lang: String (0.0)
identifier_name: String (0.0)
identifier_namespace: String (0.0)
OGRFeature(MyFeature):1
    id (String) = my_id
    identifier_name_lang (String) = en
    identifier_name (String) = my_name
    identifier_namespace (String) = baz

Example of nested element, that can be folded into main layer. Use of an attribute on a sub-element.

 
<schema xmlns:myns="http://myns"
        targetNamespace="http://myns"
        elementFormDefault="qualified"
        xmlns="http://www.w3.org/2001/XMLSchema">

<element name="AbstractFeature" abstract="true"/>

<element name="FeatureCollection">
<complexType><sequence>
    <element ref="myns:AbstractFeature" maxOccurs="unbounded"/>
</sequence></complexType>
</element>

<complexType name="namesType">
<sequence>
    <element ref="myns:name" maxOccurs="unbounded"/>
</sequence>
</complexType>

<element name="MyFeature" substitutionGroup="myns:AbstractFeature">
<complexType><sequence>
    <element name="names" type="myns:namesType"/>
    </sequence>
    <attribute name="id" type="ID" use="required"/>
</complexType>
</element>

<element name="MyFeature2" substitutionGroup="myns:AbstractFeature">
<complexType><sequence>
    <element name="names" type="myns:namesType"/>
    </sequence>
    <attribute name="id" type="ID" use="required"/>
</complexType>
</element>

<element name="name">
<complexType><sequence>
    <element name="name" type="string"/>
    <element name="lang" type="string"/>
</sequence></complexType>
</element>

</schema>

<FeatureCollection xmlns="http://myns">
    <MyFeature id="my_id">
        <names>
            <name>
            <name>name</name>
            <lang>en</lang>
            </name>
            <name>
            <name>nom</name>
            <lang>fr</lang>
            </name>
        </names>
    </MyFeature>
    <MyFeature2 id="my_id2">
        <names>
            <name>
            <name>nom2</name>
            <lang>fr</lang>
            </name>
        </names>
    </MyFeature2>
</FeatureCollection>

Layer name: name
OGRFeature(name):1
    ogr_pkid (String) = _name_1
    name (String) = name
    lang (String) = en

OGRFeature(name):2
    ogr_pkid (String) = _name_2
    name (String) = nom
    lang (String) = fr

OGRFeature(name):3
    ogr_pkid (String) = _name_3
    name (String) = nom2
    lang (String) = fr

Layer name: MyFeature
OGRFeature(MyFeature):1
    id (String) = my_id

Layer name: MyFeature2
OGRFeature(MyFeature2):1
    id (String) = my_id2

Layer name: MyFeature_names_name_name
OGRFeature(MyFeature_names_name_name):1
    occurrence (Integer) = 1
    parent_pkid (String) = my_id
    child_pkid (String) = _name_1

OGRFeature(MyFeature_names_name_name):2
    occurrence (Integer) = 2
    parent_pkid (String) = my_id
    child_pkid (String) = _name_2

Layer name: MyFeature2_names_name_name
OGRFeature(MyFeature2_names_name_name):1
    occurrence (Integer) = 1
    parent_pkid (String) = my_id2
    child_pkid (String) = _name_3

Example of of a common element "name" referenced by 2 layers "MyFeature" and "MyFeature1". The links are established through the junction layers "MyFeature_names_name_name" and "MyFeature2_names_name_name".

swe:DataArray

The following snippet

<swe:DataArray>
    <swe:elementCount>
        <swe:Count>
                <swe:value>2</swe:value>
        </swe:Count>
    </swe:elementCount>
    <swe:elementType name="Components">
        <swe:DataRecord>
                <swe:field name="myTime">
                    <swe:Time definition="http://www.opengis.net/def/property/OGC/0/SamplingTime">
                            <swe:uom xlink:href="http://www.opengis.net/def/uom/ISO-8601/0/Gregorian"/>
                    </swe:Time>
                </swe:field>
                <swe:field name="myCategory">
                    <swe:Category definition="http://dd.eionet.europa.eu/vocabulary/aq/observationverification"/>
                </swe:field>
                    <swe:field name="myQuantity">
                    <swe:Quantity definition="http://dd.eionet.europa.eu/vocabulary/aq/primaryObservation/hour">
                            <swe:uom xlink:href="http://dd.eionet.europa.eu/vocabulary/uom/concentration/ug.m-3"/>
                    </swe:Quantity>
                </swe:field>
                <swe:field name="myCount">
                    <swe:Count definition="http://"/>
                </swe:field>
                    <swe:field name="myText">
                    <swe:Text definition="http://"/>
                </swe:field>
                    <swe:field name="myBoolean">
                    <swe:Boolean definition="http://"/>
                </swe:field>
        </swe:DataRecord>
    </swe:elementType>
    <swe:encoding>
            <swe:TextEncoding decimalSeparator="." blockSeparator="@@" tokenSeparator=","/>
    </swe:encoding>
    <swe:values>2016-09-01T00:00:00+01:00,1,2.34,3,foo,true@@2017-09-01T00:00:00,2,3.45</swe:values>
</swe:DataArray>

will receive a special processing to be mapped into a dedicated layer:

Layer name: dataarray_1_components
Geometry: None
Feature Count: 2
Layer SRS WKT:
(unknown)
parent_ogr_pkid: String (0.0) NOT NULL
mytime: DateTime (0.0)
mycategory: String (0.0)
myquantity: Real (0.0)
mycount: Integer (0.0)
mytext: String (0.0)
myboolean: Integer(Boolean) (0.0)
OGRFeature(dataarray_1_components):1
  parent_ogr_pkid (String) = BAE8440FC4563A80D2AB1860A47AA0A3_DataArray_1
  mytime (DateTime) = 2016/09/01 00:00:00+01
  mycategory (String) = 1
  myquantity (Real) = 2.34
  mycount (Integer) = 3
  mytext (String) = foo
  myboolean (Integer(Boolean)) = 1

OGRFeature(dataarray_1_components):2
  parent_ogr_pkid (String) = BAE8440FC4563A80D2AB1860A47AA0A3_DataArray_1
  mytime (DateTime) = 2017/09/01 00:00:00
  mycategory (String) = 2
  myquantity (Real) = 3.45

See Also