FCM is basically use to connect to a remote system and perform actions like Create Work, Open Work etc.
Let's say you are connecting two systems using FCM : Master System (having Claim case) and Remote system (having Police Investigation case).
Now while working on Claim case in master system, you want to create a Police investigation case which is actually in some other Pega system/instance. This could be achieved by FCM using pxFCMCreateWork gadget. Now let's say you created the Police investigation case for this Claim case and you want to store this Police investigation work object id with this claim (since it is associated) with PoliceInvID property.
This is where you need to use Data mapping.
Left hand side property : .PoliceInvID = Right hand side property : .pyID
As far as I understand, what you described is mapping for case creation. But we have two types of data mapping: mapping for new case creation and mapping for opening cases. I'm asking mapping properties for opening cases. Also, I'm interesting in how technically we can use it.
I investigated this problem and have found how this works.
The mapping is only for situations, when you open a remote case with explicit use of "open gadget", which can be obtained on remote case type rule. So, in order to test it you need the following on your local (consuming) system:
1) define properties that wil recieve values from remote case in the local stub case.
2) define mapping from _published_ remote properties to just cretaed ones in your local stub case type rule.
3) include "open gadget" on your portal. The gadget, which is a section by the way, must be included using THE STUB PAGE. For example, you can define data page D_RemoteStub on the stub class, initialize property, which holds remote work hanlde, and use this data page to include "open gadget" on it.
4) after rendering the section with gadget you will see that mapped properties on the data page will be populated with the remote data. They are populated right at the moment of rendering remote content in the gadget. And don't forget to make the page editable (by default it is not).
Of course, data page is used here just like an exmaple. You may use any other type of page data (page poperty, for example).