Data Structure with multiple indexes
There are many data structures you could use for this purpose.

One possibility is a relational database (just like you've shown).

Another possibility is any data structure for storing equivalence relations; for instance, the standard Union-Find data structure would do.  Here you'd be storing that (System 1, level1-1) is equivalent to (System 2, level1-2), and so on.  That would work, too.



[ General advice for asking in the future: Don't worry too much about "names" for something.  Names matter a lot less than finding a reasonable solution.  Instead, think of the task you're trying to accomplish, what your requirements are, what you're trying to optimize, and then ask how to do that. You might get back an answer that says "read up on this standard thing"; or you might get back an answer that just directly describes a solution to your problem.  Either way, you win! ]