Release 10.1A: OpenEdge Development:
ADM Reference

ChildDataKey

When a program is run for a specific record, that is a specific customer, ChildDataKey would record that this instance of the object is for this specific piece of child data, and the key would represent the key passed into the object.

Then, when selecting a record in an object controller, you can use this key to determine if an object containing data for the selected key is already open. If that is the case, that window can be brought to the top.

Data type: CHARACTER

Notes:

Read and Write.
Used in a Progress Dynamics Dynamics environment by the Session Manager when it is keeping track of the running instance of programs.
Use this property when multiple windows are supported, and you do not want to bring up two windows containing the same child data.
ChildDataKey is an input parameter to the launch container API.