Official OAL script
First, read the OAL introduction.
From 8.0.0, you may find the OAL script at
/config/oal/*.oal of the SkyWalking dist.
You could change it, such as by adding filter conditions or new metrics. Then, reboot the OAP server, and it will come into effect.
All metrics named in this script may be used in alarm and UI query.