NOTE: Tags do not apply to Template expressions, instead you use Template Parameters.
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 Geo SCADA Expert Guide to Server Administration.
Accessing Search Key Tags (OPC Historic Data): see Access Historic Search Key Tags in the Geo SCADA Expert Guide to Core Configuration.