Tag Execution by Scan Class
Tags are executed by scan classes inside of a Tag Provider. In a typical system, there are a number of scan classes and one or more Tag Providers. Tag Providers can be either internal or external.
- Internal provider stores the Tag configuration and values inside Ignition.
Tags inside Internal Providers are available to other Ignition Gateways that use the Remote provider type.
- External provider stores Tag configuration and values in a database.
Tags stored in an external provider are available to all Ignition installations that have access to that database. One of the installations must be specified as the Tag's driver. The driving system has a copy of the scan class that it executes, which in turn evaluates the Tag. The value is stored to the database and all of the other installations are notified of the new value.
The words scan class "types" and "modes" used interchangeability
When referring to scan classes, we often use the words scan class "type" and "mode" interchangeably throughout this manual. Ignition has three scan class modes (i.e., Direct, Driven, and Leased), but there can be different variations of these modes that can change their behavior. For example, the Driven scan class has "one-shot" and "any change" options that you can set, and we often refer to these as different "types" of scan classes as well. When you create a new scan class, you will select one of the three "modes" and any properties you need to build your scan class.