9 Instances

9.1 Overview

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.

9.2 Aliases

The Aliases Node is formally defined in Table 22.

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).

9.3 TagVariables

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 23.

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.

9.4 Topics

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 24.

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.