Comment by UltraSane

Parent commenter was asking compare to datalog (not SQL) which eats recursive graph transitions like this for lunch, making the queries very elegant to read ... while still staying relational.

I'm personally of the opinion that "graph databases" should be relational databases; the relational model can subsume "graph" queries, but for all the reasons Codd laid out back in the 60s... network (aka connected graph) databases cannot do the latter.

Let the query planner figure out the connectivity story, not a hardcoded data model.

  % 1. Base case: Directly connected systems (1 hop) with   bandwidth > 10
  fast_path(StartSys, EndSys, 1) :- 
      link(StartSys, EndSys, Bandwidth), 
      Bandwidth > 10.

  % 2. Recursive case: N-hop connections via an intermediate system
  fast_path(StartSys, EndSys, Hops) :- 
      fast_path(StartSys, IntermediateSys, PrevHops), 
      link(IntermediateSys, EndSys, Bandwidth), 
      Bandwidth > 10,
      Hops = PrevHops + 1.

  % 3. The Query: Find all systems connected to 'System_A' within 5 hops
  ?- fast_path('System_A', TargetSystem, Hops), Hops <= 5.

or in RelationalAI's "Rel" language, such as I remember it, this is AI assisted it could be wrong:

  // 1. Base case: Directly connected systems (1 hop)
  def fast_path(start_sys, end_sys, hops) =
    exists(bw: link(start_sys, end_sys, bw) and bw > 10 and hops = 1)

  // 2. Recursive case: Traverse to the next system
  def fast_path(start_sys, end_sys, hops) =
    exists(mid_sys, prev_hops, bw:
      fast_path(start_sys, mid_sys, prev_hops) and
      link(mid_sys, end_sys, bw) and bw > 10 and hops = prev_hops + 1)

  // 3. The Query: Select targets connected to "System_A" within 5 hops
  def output(target_sys, hops) =
    fast_path("System_A", target_sys, hops) and hops <= 5

https://www.relational.ai/post/graph-normal-form

https://www.dataversity.net/articles/say-hello-to-graph-norm...

...

That said, modern SQL can do this just fine, just... much harder to read.

  WITH RECURSIVE fast_path AS (
    -- 1. Base case: Directly connected systems from our starting node
    SELECT
      start_sys,
      end_sys,
      1 AS hops
    FROM link
    WHERE start_sys = 'System_A' AND bandwidth > 10
    UNION ALL

    -- 2. Recursive case: Traverse to the next system
    SELECT 
      fp.start_sys, 
      l.end_sys, 
      fp.hops + 1
    FROM fast_path fp
    JOIN link l ON fp.end_sys = l.start_sys
    WHERE l.bandwidth > 10 AND fp.hops < 5
  )

  -- 3. The Query: Select the generated graph paths
  SELECT * FROM fast_path;