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AliasNameCategoryType instances are used to organize the AliasNameType instances that a Server defines. They can also include instances of AliasNameCategoryType to allow hierarchical groupings of AliasNames. It includes a mandatory Method for finding instances of AliasNameType in the AliasName hierarchy, starting at this instance of AliasNameCategoryType. For example, if the Method call is made on the Aliases AliasNameCategoryType instance (see 9.2), it would apply the AliasNameSearchPattern to all AliasNames that are defined under TagVariables, Topics and any other AliasNameCategoryType instance in the hierarchy.

The AliasNameCategoryType is a subtype of FolderType and is formally defined in Table 2.

Table 2 – AliasNameCategoryType Definition

Attribute	Value
BrowseName	AliasNameCategoryType
IsAbstract	False
References	NodeClass	BrowseName	DataType	TypeDefinition	ModellingRule
Subtype of the FolderType from OPC 10000-5
HasComponent	Object	<Alias>		AliasNameType	OptionalPlaceholder
HasComponent	Object	<SubAliasNameCategories>		AliasNameCategoryType	OptionalPlaceholder
HasComponent	Method	FindAlias	Defined in 6.3.2		Mandatory

The list of AliasNames that an Object contains may be dynamic. For example, AliasNames may be added in an aggregating Server as underlying Servers become available or may be removed if a Server is no longer available.

<Alias> represents any number of instances of AliasNameType. Each instance shall have at least one AliasFor Reference to a Node. Multiple <Alias > instances can point to the same Node.

<SubAliasNameCategories> allows the nesting or structuring of AliasNames into hierarchical groupings.

An <Alias> can appear in more than one place in the hierarchy of AliasNameCategories.