The (Legends) ranking system is described in The Essential Guide to Warfare by Del Rey (2012).
The guide describes the difference between positions and line ranks as following:
Position is an officer's current assignment to a specific ship of
unit, as opposed to permanent rank. The positions of Warlord and High
Admiral are essentially honorary, normally held by Grand Admirals and
Line rank is held by line officers, the men who command the bridge
crew, captain ships, and hoist their flag over fleets. There are very
few officers with permanent line ranks above senior captain (formally
known as captain of the line).
Out-of-universe, the inspiration seems to come from the military rank systems on Earth, with great influence of American and British systems. There are many similar rank names, with some fictional flavor added, of course.
There is a good list of naval officer ranks in Wikipedia.