what is the different between idm and 389-ds module in RHEL8 ?

As above topic. This is confuse me a lot. As i understand, on RHEL7, the idm is equivalent to ipa. I have no idea what is 389-ds ?

if i plan to implement a directory server with One Way Forest Trust from MS AD server. What should i use ? 389-ds or idm module ?

based on RHEL8 IDM setup doc , the configuration using ipa-server-install"
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html-single/installing_identity_management/index

i can't find any doc related to 389-ds in RedHat.com

Thanks