182 4 Geometry standards
The style variation element is used in cases where a symbol is displayed repeatedly, but with slight variations each time. In this case the geometry of the symbol has
to be transmitted only once.
Animation attributes are used to describe the animation behaviour of the geometry, topology, label, or graph (SMIL 2001).
XLink
XLink is an XML-technique that explicitly relates two or more data objects or
portions of data objects. XLink is widely used in GML. XLink components are used
in GML to implement associations between objects by reference. It is currently restricted to unidirectional links between two resources in most GML applications.
The associated objects may be physically as elose as two elements in the same GML
document or as far as any node in the world wide web. Further details related to
XLink are described in annex C "Extensible Marlrup Language (XML)".
Profile
A profile of GML defines a subset of the constructs of GML. GML profiles use a
"copy-and-delete-approach". To create a profile, adeveloper might copy the applicable schema files from GML and simply delete any global types, elements and local
optional partieles that he or she does not need for his or her application schema.
A profile can be the basis of an application schema. The building of an application
schema is a two-part process. The profile acts as a restrietion of GML to produce
types and elements consistent with the complete GML 3 but potentially lacking in
some optional partieles. The application schema then uses these types as a common
base, and uses them in new types and elements by extensions or inelusions.
GML 3 --- (selection and restrietion) --> GML profile --- (extension and inelusion) --> application schema
The ISO 19136 defines a set ofrules that have to be applied for creating a profile.
They can be summarized as follows:
1. A profile of GML is a logical restrietion of a subset of GML.
2. A profile must not change the name, definition, or data type of mandatory GML
elements or attributes.
3. The relevant schema or schemas that define a profile must use the core GML
namespace.
4. An application schema mayextend and use types from the profile, but must do so
in its own namespace.
Other topics of GML 3
In addition to the constructs explained above, GML offers further techniques for
the description of data elements:
1. Description of observations
2. Units, measures, and values
The style variation element is used in cases where a symbol is displayed repeatedly, but with slight variations each time. In this case the geometry of the symbol has
to be transmitted only once.
Animation attributes are used to describe the animation behaviour of the geometry, topology, label, or graph (SMIL 2001).
XLink
XLink is an XML-technique that explicitly relates two or more data objects or
portions of data objects. XLink is widely used in GML. XLink components are used
in GML to implement associations between objects by reference. It is currently restricted to unidirectional links between two resources in most GML applications.
The associated objects may be physically as elose as two elements in the same GML
document or as far as any node in the world wide web. Further details related to
XLink are described in annex C "Extensible Marlrup Language (XML)".
Profile
A profile of GML defines a subset of the constructs of GML. GML profiles use a
"copy-and-delete-approach". To create a profile, adeveloper might copy the applicable schema files from GML and simply delete any global types, elements and local
optional partieles that he or she does not need for his or her application schema.
A profile can be the basis of an application schema. The building of an application
schema is a two-part process. The profile acts as a restrietion of GML to produce
types and elements consistent with the complete GML 3 but potentially lacking in
some optional partieles. The application schema then uses these types as a common
base, and uses them in new types and elements by extensions or inelusions.
GML 3 --- (selection and restrietion) --> GML profile --- (extension and inelusion) --> application schema
The ISO 19136 defines a set ofrules that have to be applied for creating a profile.
They can be summarized as follows:
1. A profile of GML is a logical restrietion of a subset of GML.
2. A profile must not change the name, definition, or data type of mandatory GML
elements or attributes.
3. The relevant schema or schemas that define a profile must use the core GML
namespace.
4. An application schema mayextend and use types from the profile, but must do so
in its own namespace.
Other topics of GML 3
In addition to the constructs explained above, GML offers further techniques for
the description of data elements:
1. Description of observations
2. Units, measures, and values