Yes the Junos interface naming convention is very standardized as follows:
XX-99/99/99.999
The values to the left of the period represent the physical interface name, where XX is the interface type:
ge, xe, vlan, etc . . .
and 99/99/99 represent the line card / interface card / port #
Then the value(s) to the right of the period represent the naming of the logical interface:
.0 is a standard (non vlan) based logical IF for ge, xe, fe, etc.
.999 could be a vlan IF or some other type of logical IF.
You can configure / access the logical I/F's by using either of the two conventions
user@host# set interfaces xx-99/99/99.999 . . . .
or
user@host# set interfaces xx-99/99/99 unit 999 . . . .
Hope this provides you with your answer.