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
OrganizedBy by the Aliases defined in 9.2
|HasTypeDefinition||ObjectType||AliasNameCategoryType||Defined in 6.3|
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.