I am doing some scripts with the Web API and Curl, and this problem
arised when I was trying to add a child link to a WI.

I found out there are two ways(at least) to identify a WI:
1-https://localhost:9443/jazz/oslc/workitems/232.xml
2-https://localhost:9443/jazz/resource/itemOid/com.ibm.team.workitem.WorkItem/_v_OOMEIkEd-LWZ-HXG-mhg

I have access to the first way, but when adding a child relationship,
I need the WI in the second form.

Is there any way to transform from one to another?

Usually, you would get the URL from a query. Either using the OSLC-CM
query syntax or the delegated picker UI. You shouldn't rely on a
specific URL pattern and assemble it yourself.

The change request representation also contains a canonical reference to
itself. E.g. the XML for .../jazz/oslc/workitems/232.xml contains:

<oslc_cm>
....

If really nothing else helps, you can also use this URL format:

https://localhost:9443/jazz/resource/itemName/com.ibm.team.workitem.WorkItem/232

--
Regards,
Patrick
Jazz Work Item Team