Rockwell Automation Logix5000 Controllers I/O and Tag Data Programming Manual - Manual (Page 48)

Chapter 2 Organize tags
The tags window displays alias information.
Item Description
drill_1_depth_limit is an alias for Local:2:I.Data.3 (a digital input point). When the input turns on, the alias
tag also turns on.
drill_1_on is an alias for Local:0:O.Data.2 (a digital output point). When the alias tag turns on, the output
tag also turns on.
north_tank is an alias for tanks[0,1].
The (C) indicates that the tag is at the controller scope.
A common use of alias tags is to program logic before wiring diagrams are available.
1. For each I/O device, create a tag with a name that describes the device, such
as conveyor for the conveyor motor.
2. Program your logic by using the descriptive tag names.
You can even test your logic without connecting to the I/O.
3. Later, when wiring diagrams are available, add the I/O modules to the I/O
configuration of the controller.
4. Finally, convert the descriptive tags to aliases for their respective I/O points
or channels.
48 Rockwell Automation Publication 1756-PM004E-EN-P - October 2014