Technical Reference Manual - InduSoft

Introduction
Note: Tags are variables (such as communication points in field equipment, calculation results,
alarm points, and so on) that are used in screens and worksheets. For more information, see About
Tags and the Project Database on page 109.
The architecture of the IWS project runtime
Each IWS module contains a virtual table of the tags that are relevant for that module at the current time.
The tags database uses this table to determine which information must be updated in each module. For
example, the Viewer contains a virtual table that lists all tags configured for all of the open project screens. If
a tag value changes, the tags database sends a message to the Viewer, and then the Viewer updates the value
in all objects where the tag is configured.
For example, if a driver reads a new value from the PLC, the driver updates the tag associated with this value
in the tags database. Then, if this new information must display on the project screen, the tags database
sends the new tag value to the Viewer task, and the Viewer updates the screen.
An example of data flow
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