Changes for page 8 Hierarchy

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5	5	== 8.1 Scope ==
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7		-The [[Codelist>>doc:sdmx:Glossary 2\.1.Code list.WebHome]] described in the section on structural definitions supports a simple [[hierarchy>>doc:sdmx:Glossary 2\.1.Hierarchy.WebHome]] of Codes and restricts any [[child>>doc:IMElements.child.WebHome]] [[Code>>doc:IMElements.AnnotableArtefact.IdentifiableArtefact.NameableArtefact.Item.Code.WebHome]] to having just one [[parent>>doc:IMElements.parent.WebHome]] [[Code>>doc:IMElements.AnnotableArtefact.IdentifiableArtefact.NameableArtefact.Item.Code.WebHome]]. Whilst this [[structure>>doc:IMElements.structure.WebHome]] is useful for supporting the needs of the [[DataStructureDefinition>>doc:IMElements.AnnotableArtefact.IdentifiableArtefact.NameableArtefact.VersionableArtefact.MaintainableArtefact.Structure.DataStructureDefinition.WebHome]] and the [[MetadataStructureDefinition>>doc:IMElements.AnnotableArtefact.IdentifiableArtefact.NameableArtefact.VersionableArtefact.MaintainableArtefact.Structure.MetadataStructureDefinition.WebHome]], it may not be sufficient for supporting the more complex associations between codes that are often found in coding schemes such as a [[classification>>doc:sdmx:Glossary 2\.1.Statistical Classification.WebHome]] scheme. Often, the [[Codelist>>doc:sdmx:Glossary 2\.1.Code list.WebHome]] used in a [[DataStructureDefinition>>doc:IMElements.AnnotableArtefact.IdentifiableArtefact.NameableArtefact.VersionableArtefact.MaintainableArtefact.Structure.DataStructureDefinition.WebHome]] is derived from a more complex coding scheme. Access to such a coding scheme can aid applications, such as OLAP applications or data visualisation systems, to give more views of the data than would be possible with the simple [[Codelist>>doc:sdmx:Glossary 2\.1.Code list.WebHome]] used in the [[DataStructureDefinition>>doc:IMElements.AnnotableArtefact.IdentifiableArtefact.NameableArtefact.VersionableArtefact.MaintainableArtefact.Structure.DataStructureDefinition.WebHome]]. A [[Hierarchy>>doc:sdmx:Glossary 2\.1.Hierarchy.WebHome]] may be linked to an IndentifiableArtefact, in order to assist.
	7	+The [[Codelist>>doc:sdmx:Glossary 2\.1.Code list.WebHome]] described in the section on structural definitions supports a simple [[hierarchy>>doc:sdmx:Glossary 2\.1.Hierarchy.WebHome]] of [[Codes>>doc:sdmx:Glossary 2\.1.Code.WebHome]] and restricts any child [[Code>>doc:sdmx:Glossary 2\.1.Code.WebHome]] to having just one parent [[Code>>doc:sdmx:Glossary 2\.1.Code.WebHome]]. Whilst this structure is useful for supporting the needs of the DataStructureDefinition and the MetadataStructureDefinition, it may not be sufficient for supporting the more complex associations between [[codes>>doc:sdmx:Glossary 2\.1.Code.WebHome]] that are often found in coding schemes such as a [[classification>>doc:sdmx:Glossary 2\.1.Statistical Classification.WebHome]] scheme. Often, the [[Codelist>>doc:sdmx:Glossary 2\.1.Code list.WebHome]] used in a DataStructureDefinition is derived from a more complex coding scheme. Access to such a coding scheme can aid applications, such as OLAP applications or data visualisation systems, to give more views of the data than would be possible with the simple [[Codelist>>doc:sdmx:Glossary 2\.1.Code list.WebHome]] used in the DataStructureDefinition. A [[Hierarchy>>doc:sdmx:Glossary 2\.1.Hierarchy.WebHome]] may be linked to an IndentifiableArtefact, in order to assist.
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9	9	Note that a [[Hierarchy>>doc:sdmx:Glossary 2\.1.Hierarchy.WebHome]] is not necessarily a balanced tree. A balanced tree is where
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11		-levels are pre-defined and fixed, (i.e. a level always has the same set of codes, and any code has a fixed [[parent>>doc:IMElements.parent.WebHome]] and [[child>>doc:IMElements.child.WebHome]] relationship to other codes). A [[statistical classification>>doc:sdmx:Glossary 2\.1.Statistical Classification.WebHome]] is an example of a balanced tree, and the support for a balanced [[hierarchy>>doc:sdmx:Glossary 2\.1.Hierarchy.WebHome]] is a subset, and special case, of [[hierarchies>>doc:sdmx:Glossary 2\.1.Hierarchy.WebHome]].
	11	+(% style="color:#e74c3c" %)levels(%%) are pre-defined and fixed, (i.e. a (% style="color:#e74c3c" %)level(%%) always has the same set of [[codes>>doc:sdmx:Glossary 2\.1.Code.WebHome]], and any [[code>>doc:sdmx:Glossary 2\.1.Code.WebHome]] has a fixed parent and child relationship to other [[codes>>doc:sdmx:Glossary 2\.1.Code.WebHome]]). A [[statistical classification>>doc:sdmx:Glossary 2\.1.Statistical Classification.WebHome]] is an example of a balanced tree, and the support for a balanced [[hierarchy>>doc:sdmx:Glossary 2\.1.Hierarchy.WebHome]] is a subset, and special case, of [[hierarchies>>doc:sdmx:Glossary 2\.1.Hierarchy.WebHome]].
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13	13	The principal features of the [[Hierarchy>>doc:sdmx:Glossary 2\.1.Hierarchy.WebHome]] are:
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15		-1. A [[child>>doc:IMElements.child.WebHome]] code can have more than one [[parent>>doc:IMElements.parent.WebHome]].
16		-1. There can be more than one code that has no [[parent>>doc:IMElements.parent.WebHome]] (i.e. more than one “root node”).
17		-1. The levels in a [[hierarchy>>doc:sdmx:Glossary 2\.1.Hierarchy.WebHome]] can be explicitly defined or they can be implicit: i.e. they exist only as [[parent>>doc:IMElements.parent.WebHome]]/[[child>>doc:IMElements.child.WebHome]] relationships in the coding [[structure>>doc:IMElements.structure.WebHome]].
	15	+1. A child [[code>>doc:sdmx:Glossary 2\.1.Code.WebHome]] can have more than one parent.
	16	+1. There can be more than one [[code>>doc:sdmx:Glossary 2\.1.Code.WebHome]] that has no parent (i.e. more than one “root node”).
	17	+1. The (% style="color:#e74c3c" %)levels(%%) in a [[hierarchy>>doc:sdmx:Glossary 2\.1.Hierarchy.WebHome]] can be explicitly defined or they can be implicit: i.e. they exist only as parent/child relationships in the coding structure.
18	18	1. [[Hierarchies>>doc:sdmx:Glossary 2\.1.Hierarchy.WebHome]] may be associated to the structures they refer to, via the HierarchyAssociation.
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20	20	== 8.2 Inheritance ==