GML Model and Syntax

1
GML Model and Syntax

• Courtesy of Galdos Systems Inc
• This presentation provides a short GML basic
  concept review, which is intended to facilitate
  the understanding of the AIXM Schema structure.

2
GML Model and Syntax

• Topics
• GML model Object-Property-Value
• XML Syntax representation
• Lexical conventions

3
GML Conceptual Model

• The basic constructs of the GML data model are
  object and property.
• GML object - an entity represents a real word
  entity but with a more generic meaning to
  represent any meaningful thing in an application
  context.
• GML property - an attribute of objects or
  relationships between entity objects.

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XML Syntax Representation

• A GML object is encoded as an XML element with a
  type definition that is derived from the GML
  predefined type gmlAbstractGMLType.
• The properties of the GML object are represented
  as sub-elements of the corresponding GML object
  element.

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Example GML Representation
ltRoadgt ltnamegtlt/namegt ltnumOfLanesgt lt/numOfL
anesgt ltshapegtlt/shapegt lt/Roadgt
Road
name
numOfLanes
shape
GML Representation of Road Feature
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Property Value RepresentationInline

• Inline the value of the property is encoded as
  content of the property element.
• simple valued property the value is encoded as
  XML text content of the property element
• complex valued property the value is encoded as
  a sub-element of the property element.

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Example for Value Representation
Simple value encoded as text content
ltRoadgt ltgmlnamegtCambie Streetlt/gmlnamegt
ltnumOfLanesgt4lt/numOfLanesgt ltshapegt
ltgmlLineStringgt lt/gmlLineStringgt
lt/shapegt lt/Roadgt
Complex value encoded as a sub-element
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Property Value Representation By Reference

• By reference the value is identified by
  xlinkhref.

ltObjectAgt ltproperty1 xlinkhrefhttp//www.el
sewhere.org/remoteGML.xmlB_1/gt ltproperty2
xlinkhrefRoad_1gt lt/ObjectAgt ltRoad
gmlidRoad_1gt ltgmlnamegt lt/Roadgt
ltObjectB gmlidB_1gt ltpropertyb1gt ltpropertyb2gt
lt/ObjectBgt
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Property Value RepresentationMultiple-Valued
Property (Possibilities)

• ltObjectElementgt
• ltmultipleValuedPropertygt
• ltValueObjectgt
• ltValueObjectgt
• ltValueObjectgt
• lt/multipleValuedPropertygt
• lt/ObjectElementgt
• Note Single property element with multiple value
  objects as itd content.

ltObjectElementgt ltmultipleValuedPropertygt ltValue
Objectgt lt/multipleValuedPropertygt ltmultipleValue
dPropertygt ltValueObjectgt lt/multipleValuedProper
tygt lt/ObjectElementgt Note multiple property
elements, each of them contains a single value
object.
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Ownership of Property Values

• The owns attribute may be added to property
  elements to indicate whether the value is owned
  by the parent object.
• ltObjectElementgt
• ltpropertyElement ownstruegt
• ltValueObjectgt
• lt/propertyElementgt
• lt/ObjectElementgt
• The true value of the attribute owns
  indicates the ltValueObjectgt.
• is owned by the ltObjectElementgt.
• delete ltObjectElementgt delete ltValueObjectgt

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Lexical Convention

• Object names UpperCamelCase
• Property names lowerCamelCase
• Abstract object names Abstract object name
• Abstract property names abstract property
  name
• Complex type names UpperCamelCase Type
• Abstract complex type names Abstract
  complex type name

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XML Tree Structure for GML Object

• ltObjectgt
• ltproperty1gtsimple valued lt/property1gt
• ltproperty2 ownstruegt
• ltValueObjectgtlt/ValueObjectgt
• lt/property2gt
• ltproperty3 ownsfalse xlinkhrefgt
• lt/Objectgt