The following standard Objects are defined for maintaining the hierarchical structure of AliasNameCategories in a Server. Server vendors are free to add additional instances of AliasNameCategoryType under this hierarchy.

The Aliases Node is formally defined in Table 9.

Table 9 – Aliases definition

Attribute	Value
BrowseName	Aliases
References	NodeClass	BrowseName	DataType	TypeDefinition
OrganizedBy by the Objects Folder defined in OPC 10000-5
HasTypeDefinition	ObjectType	AliasNameCategoryType	Defined in 6.3
HasProperty	Variable	LastChange	VersionTime	PropertyType
ConformanceUnits
AliasName Hierarchy

This is the root folder for all alias related Objects. It can contain instances of AliasNameType Objects and / or instances of AliasNameCategoryType Objects.

The LastChange Property, which is optional in the AliasNameCategoryType, shall be present for the root Aliases instance. This property shall reflect the last time any changes to AliasName occurred (see 6.3).

TagVariables is an instance of AliasNameCategoryType. TagVariables shall restrict instances of AliasNameType to those that have an AliasFor References that point to Variables. The TagVariables instance is formally defined in Table 10.

Table 10 – TagVariables definition

Attribute	Value
BrowseName	TagVariables
References	NodeClass	BrowseName	DataType	TypeDefinition
OrganizedBy by the Aliases defined in 9.2
HasTypeDefinition	ObjectType	AliasNameCategoryType	Defined in 6.3
ConformanceUnits
AliasName Category Tags

This is the root folder for AliasNameType instances that contain an AliasFor reference to Variables. It can contain additional AliasNameCategoryType Objects, which could be used to create a hierarchy. A single instance of AliasNameType can exist in more than one location in the Alias hierarchy.

Topics is an instance of AliasNameCategoryType. Topics shall restrict instances of AliasNameType to only have AliasFor References that point to PublishedDataSetType (or subtypes) instances (PublishedDataSetType is defined in OPC 10000-14). The Topics Node instance is formally defined in Table 11.

Table 11 – Topics definition

Attribute	Value
BrowseName	Topics
References	NodeClass	BrowseName	DataType	TypeDefinition
OrganizedBy by the Aliases defined in 9.2
HasTypeDefinition	ObjectType	AliasNameCategoryType	Defined in 6.3
ConformanceUnits
AliasName Category Topics

It can contain additional AliasNameCategoryType Objects, which could be used to create a hierarchy or other structure. A single instance of AliasNameType can exist in more than one location in the hierarchy, but all instances in the Topics hierarchy must point to an instance of a PublishedDataSetType.