SWE Common Data Model 2.0 Encoding Rule

The following is a list of schema conversion rules that apply to the SWE Common Data Model 2.0 encoding rule. These are in addition to the common conversion rules.

Since the SWE Common Data Model 2.0 encoding rule has been developed using the GML 3.2 encoding rule as a starting point, it shares a large number of conversion rules with the GML 3.2 encoding rule.

The standard itself lists the following differences from the GML 3.2 encoding rule in Annex C:

Relaxed rule on the mandatory ‘id’ attribute that is kept optional in the SWE Common Data Model schemas.

Introduced the additional XMI tagged value ‘soft-typed’, so that soft-typed- properties can be encoded in XML with an additional ‘name’ attribute.

Added support for encoding certain simple-type properties as XML attributes by introducing the additional XMI tagged value ‘asXMLAttribute’.

Use different base type for <<Type>> stereotype (Elements are derived from swe:AbstractSWE instead of gml:AbstractGML).

However, in reality the differences are greater and additional conversion rules have been added to be able to generate XML Schema that reflects the XSDs of SWE Common Data Model 2.0 (note that basicTypes.xsd as it is can only be constructed manually and not by automated conversion).

Note also that SWE Common claims in its Foreword that “all elements are substitutable for gml:AbstractValue (and thus transitively for gml:AbstractObject) so that they can be used directly by GML application schemas.” This seems to be an outdated statement as it is not correct.

Rule	Description
rule-xsd-cls-codelist-asDictionary	If a the tagged value asDictionary of a code list is not ‘true’, create a global type for the code list; otherwise reference code list values using gml:CodeType
rule-xsd-cls-noPropertyType	If a the tagged value noPropertyType of a feature type, class, data type or union type is ‘true’, the property type creation is suppressed
rule-xsd-cls-byValuePropertyType	If a the tagged value byValuePropertyType of a feature type or class is ‘true’, an additional by-value property type is created
rule-xsd-pkg-gmlProfileSchema	Include gmlProfileSchema appinfo, if the tagged value is set on the application schema package
rule-xsd-prop-defaultCodeSpace	Include defaultCodeSpace appinfo, if applicable
rule-xsd-prop-inlineOrByReference	Take tagged value inlineOrByReference on properties into account when setting the type of a property element
rule-xsd-prop-reverseProperty	Include reversePropertyName appinfo, if applicable
rule-xsd-prop-targetElement	Include targetElement appinfo, if a property is byReference
rule-xsd-cls-global-enumeration	Convert enumerations to global types
rule-xsd-all-naming-swe	Use the naming strategy for schema components as specified by SWE Common Data Model 2.0
rule-xsd-cls-standard-swe-property-types	Use the strategy for property types as specified by SWE Common Data Model 2.0
rule-xsd-cls-union-as-group-property-type	Encode <<union>> types as groups
rule-xsd-prop-xsdAsAttribute	Support tagged values xsdAsAttribute / asXmlAttribute
rule-xsd-prop-soft-typed	Support tagged value “soft-typed” to encode properties as XML elements with a generic element name but provide a “name” attribute for further disambiguation.
rule-xsd-prop-initialValue	Support default and fixed values

rule-xsd-cls-codelist-asDictionary

If a the tagged value asDictionary of a code list is not ‘true’, create a global type for the code list; otherwise reference code list values using gml:CodeType

rule-xsd-cls-noPropertyType

If a the tagged value noPropertyType of a feature type, class, data type or union type is ‘true’, the property type creation is suppressed

rule-xsd-cls-byValuePropertyType

If a the tagged value byValuePropertyType of a feature type or class is ‘true’, an additional by-value property type is created

rule-xsd-cls-standard-gml-property-types

Reuse property types or create anonymous property types according to GML 3.2

rule-xsd-pkg-gmlProfileSchema

Include gmlProfileSchema appinfo, if the tagged value is set on the application schema package

rule-xsd-prop-defaultCodeSpace

Include defaultCodeSpace appinfo, if applicable

rule-xsd-prop-inlineOrByReference

Take tagged value inlineOrByReference on properties into account when setting the type of a property element

rule-xsd-prop-reverseProperty

Include reversePropertyName appinfo, if applicable

rule-xsd-prop-targetElement

Include targetElement appinfo, if a property is byReference

rule-xsd-cls-global-enumeration

Convert enumerations to global types

rule-xsd-all-naming-swe

Use the naming strategy for schema components as specified by SWE Common Data Model 2.0

The difference to the GML 3.2 naming strategy is that a new abstract base type / element is used. A custom base element “AbstractSWE” and a base type “AbstractSWEType” is used for all complex types in the a SWE-Common-based schema.

rule-xsd-cls-standard-swe-property-types

The conversion rules for reusing existing or creating new property types are similar to those in GML 3.2, with the following differences:

SWE Common specifies its own swe:AssociationAttributeGroup attribute group and swe:ReferenceType with a similar content model as the GML 3.2 equivalents.
Property values from a code list are referenced using Xlinks like in the GML 3.3 encoding rule.
Soft-typed properties are treated differently, see rule-xsd-prop-soft-typed.

rule-xsd-cls-union-as-group-property-type

<<union>> types are encoded as groups and property types reference these groups.

For example, the <<union>> Quality is

<group name="Quality">
 <choice>
  <element ref="swe:Quantity"/>
  <element ref="swe:QuantityRange"/>
  <element ref="swe:Category"/>
  <element ref="swe:Text"/>
 </choice>
</group>

<complexType name="QualityPropertyType">
 <sequence minOccurs="0">
  <group ref="swe:Quality"/>
 </sequence>
 <attributeGroup ref="swe:AssociationAttributeGroup"/>
</complexType>

rule-xsd-prop-xsdAsAttribute

If the tagged value ‘asXMLAttribute’ (or ‘xsdAsAttribute’) is set to ‘true’ on a property, the property has a maximum multiplicity of 1 and the value of the property is simple, the property is converted to an XML attribute instead of an XML element.

For example, the property “referenceFrame” in Vector is encoded as:

<attribute name="referenceFrame" type="anyURI" use="required"/>

rule-xsd-prop-soft-typed

Properties with a tagged value “soft-typed” with a value “true” are encoded as XML elements with a generic element name but provide an additional NCName-valued “name” attribute for further disambiguation.

For example, the property “field” in DataRecord is encoded as:

<element maxOccurs="unbounded" minOccurs="1" name="field">
 <complexType>
  <complexContent>
   <extension base="swe:AbstractDataComponentPropertyType">
    <attribute name="name" type="NCName" use="required"/>
   </extension>
  </complexContent>
 </complexType>
</element>

rule-xsd-prop-initialValue

If an attribute has an initial value, it is converted to a default value in XML Schema. If the attribute carries the constraint “{frozen}”, too, the initial value is converted to a fixed element value in XML Schema.