Going through Corticon User Guide... Very well written documentation. There are some, very infrequent glitches. Here is one. In "Path 2 - Using Bundled Sample Code to Consume a Decision Service"->"Creating a Request Message for a Decision Service" the guide tells to "Set a work document entity (WDE) for the Ruleflow".
Whatever I did I couldn't find anything in Corticon eStudio that used either WDE or "Work document entity" terminology. So I settled with "Rulesheet Activity" as presented on the following screenshot:
Please note that to see the Rulesheet Activity and be able to change it to Cargo.ers you need to double-click on tutorial_example.erf. If you do a single click you'll see a different view: