Mainframe security and building alerts into SIEM - any advice or thoughts? What questions/research should I being doing?

Not even sure where to properly start - first off, I have no experience with mainframes beyond basic concept of what a mainframe is at a high level.

Got an email that we are going to be potentially receiving alerts into our SIEM.

* My immediate thought was who/how was the mainframe being handled prior to this?
* Why and who is pushing this - where did the requirement come from and why now?
* Does any documentation exist?
* …

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