In Taverna 2.3 and earlier, Text Constant was known as String Constant.
A Text constant service allows you to set a fixed-value input for a service or the whole workflow. This is useful for inputs that are fixed across multiple runs of the same workflow, and also for publishing your workflows since the string constant provides an example input for people wanting to try out the workflow.
Note that you can add a Text constant from the Insert menu as well.
The value for a Text constant can be loaded from a file, saved to a file or cleared.
When you load the text from a file, it copies the text into the text constant. If you later change the file, then this has no effect on the text constant.
Alternatively, you can drag in a Text Constant from the Service Templates section of the Service Panel, as explained in the previous section, and connect it to the appropriate input port of your service.