Entities as described earlier are based on the table and column names within the database, if you are unsure of what the entity is you want then have a browse around inside MySQL using show tables and desc <tablename>.
Below are some common entities that you can use within the alerting system. This list is not exhaustive and you should look at the MySQL database schema for the full list.
The device hostname
The device sysName
The device sysDescr
The device hardware
The device os version
The device location
The status of the device, 1
The reason the device was detected as down (icmp or snmp)
If the device is ignored this will be set to 1
If the device is disabled this will be set to 1
The the last polled datetime (yyyy-mm-dd hh:mm:ss)
The device type such as network, server, firewall, etc.
This is the description of the BGP Peer
The IP address of the BGP Peer
The AS number of the BGP Peer
The operational state of the BGP session
The administrative state of the BGP session
The local address of the BGP session.
The remote VPN peer address
The local VPN address
The VPN tunnels operational status.
The memory pool type such as hrstorage, cmp and cemp
The description of the pool such as Physical memory, Virtual memory and System memory
The used percentage of the memory pool.
The interface description
The interface name
The port speed in bps
The port speed in mbps
The operational status of the port (up or down)
The administrative status of the port (up or down)