Some Data Source types provide the ability to configure a “Custom Expression”, rather than using one of the standard aggregation methods. Custom expressions allow for the querying of more than one tag from the data source.
The results of the query are transposed into a “data” object that returns a set of columns containing the tag values and qualities. The custom expression uses Microsoft.NET’s C# syntax. A single “Result” object must be returned by the custom expression.
The custom expression must be validated before being saved.
Custom expressions can be used for custom calculations (e.g. integrate one tag by another), lookups (e.g. convert the returned values based on a lookup table), etc.