You can use search keys as an alternative to name fields to identify database items. In certain circumstances, using search keys can provide a more effective way of referencing historic tags in your expressions.
Search keys for OPC historic tags work in a similar way to search keys for OPC data tags, see Search Key Tags.
Further Information
Configuring Search Keys: see Extra Database Fields in the ClearSCADA Guide to Server Administration.
Accessing Search Key Tags (OPC Historic Data): see Access Historic Search Key Tags in the ClearSCADA Guide to Core Configuration.