Create a new empty project in IntelliJ or use an existing one. In your main resources directory, create a directory named “mappings” to hold your DataSonnet files. Create a new file called “mapping.ds” (or any other name with that suffix). When you open that file, you’ll see three panes (though one will not be very visible, on the left). Click the left-most + on the left-most pane to add a Scenario, which is a grouping of inputs useful for testing the DataSonnet transformation. That creates a directory in your test resources.
You’ll see a second + to the right of the first. Click that to add an input file. Name it something like “payload” or “input”. (Note: if you want to try the Example above without modification, you must name it “payload”). The name of each of your input files will be the name of the variable in your transformation. You should use the name “payload” for the input that will receive the main payload during a transformation, as that’s what other tooling assumes. You can add as many inputs as you would like.
Write your DataSonnet transformation in the second pane. You can use the variables defined by your inputs there. (If your transformation isn’t running automatically, click the “refresh” icon on the left of the third pane, which will rerun the transformation with the current Scenario.)