See ISO/DIS 19136 7.2.
The gmlBase schema components establish the GML model and syntax, in particular
- a root XML type from which XML types for all GML objects should be derived,
- a pattern and components for GML properties,
- patterns for collections and arrays, and components for generic collections and arrays,
- components for associating metadata with GML objects,
- components for constructing definitions and dictionaries.
Application Data
gmlBase.xsd More information at: urn:ogc:specification:gml:schema-xsd:gmlBase:3.2.0.
</sch:title><sch:ns prefix="gml" uri="http://www.opengis.net/gml"/><sch:ns prefix="xlink" uri="http://www.w3.org/1999/xlink"/><sch:pattern name="Check either href or content not both">
The attribute gml:id supports provision of a handle for the XML element representing a GML Object. Its use is mandatory for all GML objects. It is of XML type ID, so is constrained to be unique in the XML document within which it occurs.
The abstract element gml:AbstractGML is “any GML object having identity”. It acts as the head of an XML Schema substitution group, which may include any element which is a GML feature, or other object, with identity. This is used as a variable in content models in GML core and application schemas. It is effectively an abstract superclass for all GML objects.
This element has no type defined, and is therefore implicitly (according to the rules of W3C XML Schema) an XML Schema anyType. It is used as the head of an XML Schema substitution group which unifies complex content and certain simple content elements used for datatypes in GML, including the gml:AbstractGML substitution group.
Applying this pattern shall restrict the multiplicity of objects in a property element using this content model to exactly one. An instance of this type shall contain an element representing an object, or serve as a pointer to a remote object.
Applying the pattern to define an application schema specific property type allows to restrict
- the inline object to specified object types,
- the encoding to „by-reference only“ (see 7.2.3.7),
- the encoding to „inline only“ (see 7.2.3.8).
This element shows how an element
declaration may include a Schematron constraint to limit the property to act
in either inline or by-reference mode, but not both.
The value of this property is a text description of the object. gml:description uses gml:StringOrRefType as its content model, so it may contain a simple text string content, or carry a reference to an external description. The use of gml:description to reference an external description has been deprecated and replaced by the gml:descriptionReference property.
The value of this property is a remote text description of the object. The xlink:href attribute of the gml:descriptionReference property references the external description.
Often, a special identifier is assigned to an object by the maintaining authority with the intention that it is used in references to the object For such cases, the codeSpace shall be provided. That identifier is usually unique either globally or within an application domain. gml:identifier is a pre-defined property for such identifiers.
The gml:name property provides a label or identifier for the object, commonly a descriptive name. An object may have several names, typically assigned by different authorities. gml:name uses the gml:CodeType content model. The authority for a name is indicated by the value of its (optional) codeSpace attribute. The name may or may not be unique, as determined by the rules of the organization responsible for the codeSpace. In common usage there will be one name per authority, so a processing application may select the name from its preferred codeSpace.
If the value of an object property is another object and that object contains also a property for the association between the two objects, then this name of the reverse property may be encoded in a gml:reversePropertyName element in an appinfo annotation of the property element to document the constraint between the two properties. The value of the element shall contain the qualified name of the property element.
A GML Object Collection is any GML Object with a property element in its content model whose content model is derived by extension from gml:AbstractMemberType.
In addition, the complex type describing the content model of the GML Object Collection may also include a reference to the attribute group gml:AggregationAttributeGroup to provide additional information about the semantics of the object collection. This information may be used by applications to group GML objects, and optionally to order and index them.
The allowed values for the aggregationType attribute are defined by gml:AggregationType. See 8.4 of ISO/IEC 11404:1996 for the meaning of the values in the enumeration.
XLink components are the standard method to support hypertext referencing in XML. An XML Schema attribute group, gml:AssociationAttributeGroup, is provided to support the use of Xlinks as the method for indicating the value of a property by reference in a uniform manner in GML.
Encoding a GML property inline vs. by-reference shall not imply anything about the “ownership” of the contained or referenced GML Object, i.e. the encoding style shall not imply any “deep-copy” or “deep-delete” semantics. To express ownership over the contained or referenced GML Object, the gml:OwnershipAttributeGroup attribute group may be added to object-valued property elements. If the attribute group is not part of the content model of such a property element, then the value may not be “owned”.
When the value of the owns attribute is "true", the existence of inline or referenced object(s) depends upon the existence of the parent object.
To create a collection of GML Objects that are not all features, a property type shall be derived by extension from gml:AbstractMemberType.
This abstract property type is intended to be used only in object types where software shall be able to identify that an instance of such an object type is to be interpreted as a collection of objects.
By default, this abstract property type does not imply any ownership of the objects in the collection. The owns attribute of gml:OwnershipAttributeGroup may be used on a property element instance to assert ownership of an object in the collection. A collection shall not own an object already owned by another object.
To associate metadata described by any XML Schema with a GML object, a property element shall be defined whose content model is derived by extension from gml:AbstractMetadataPropertyType.
The value of such a property shall be metadata. The content model of such a property type, i.e. the metadata application schema shall be specified by the GML Application Schema.
By default, this abstract property type does not imply any ownership of the metadata. The owns attribute of gml:OwnershipAttributeGroup may be used on a metadata property element instance to assert ownership of the metadata.
If metadata following the conceptual model of ISO 19115 is to be encoded in a GML document, the corresponding Implementation Specification specified in ISO/TS 19139 shall be used to encode the metadata information.
The XML Instance Representation table above shows the schema component's content as an XML instance.
The minimum and maximum occurrence of elements and attributes are provided in square brackets, e.g. [0..1].
Model group information are shown in gray, e.g. Start Choice ... End Choice.
For type derivations, the elements and attributes that have been added to or changed from the base type's content are shown in bold.
If an element/attribute has a fixed value, the fixed value is shown in green, e.g. country="Australia".
Otherwise, the type of the element/attribute is displayed.
If the element/attribute's type is in the schema, a link is provided to it.
For local simple type definitions, the constraints are displayed in angle brackets, e.g. <<pattern = [1-9][0-9]{3}>>.
If a local element/attribute has documentation, it will be displayed in a window that pops up when the question mark inside the attribute or next to the element is clicked, e.g. <postcode>.
Abstract(Applies to complex type definitions and element declarations). An abstract element or complex type cannot used to validate an element instance. If there is a reference to an abstract element, only element declarations that can substitute the abstract element can be used to validate the instance. For references to abstract type definitions, only derived types can be used.
Collapse Whitespace PolicyReplace tab, line feed, and carriage return characters with space character (Unicode character 32). Then, collapse contiguous sequences of space characters into single space character, and remove leading and trailing space characters.
Disallowed Substitutions(Applies to element declarations). If substitution is specified, then substitution group members cannot be used in place of the given element declaration to validate element instances. If derivation methods, e.g. extension, restriction, are specified, then the given element declaration will not validate element instances that have types derived from the element declaration's type using the specified derivation methods. Normally, element instances can override their declaration's type by specifying an xsi:type attribute.
Nillable(Applies to element declarations). If an element declaration is nillable, instances can use the xsi:nil attribute. The xsi:nil attribute is the boolean attribute, nil, from the http://www.w3.org/2001/XMLSchema-instance namespace. If an element instance has an xsi:nil attribute set to true, it can be left empty, even though its element declaration may have required content.
Prohibited Derivations(Applies to type definitions). Derivation methods that cannot be used to create sub-types from a given type definition.
Prohibited Substitutions(Applies to complex type definitions). Prevents sub-types that have been derived using the specified derivation methods from validating element instances in place of the given type definition.
Replace Whitespace PolicyReplace tab, line feed, and carriage return characters with space character (Unicode character 32).
Substitution GroupElements that are members of a substitution group can be used wherever the head element of the substitution group is referenced.
Substitution Group Exclusions(Applies to element declarations). Prohibits element declarations from nominating themselves as being able to substitute a given element declaration, if they have types that are derived from the original element's type using the specified derivation methods.
Target NamespaceThe target namespace identifies the namespace that components in this schema belongs to. If no target namespace is provided, then the schema components do not belong to any namespace.