Best Way to Store/Access a Directed Graph

Question

I have around 3500 flood control facilities that I would like to represent as a network to determine flow paths (essentially a directed graph). I\'m currently using SqlServer an

Answer 1

I know nothing about flood control facilities. But I would take the first facility. And use a temp table and a while loop to generate the path.

-- Pseudo Code
TempTable (LastNode, CurrentNode, N)


DECLARE @intN INT
SET @intN = 1

INSERT INTO TempTable(LastNode, CurrentNode, N)
  -- Insert first item in list with no up stream items...call this initial condition
  SELECT LastNode, CurrentNode, @intN
  FROM your table
  WHERE node has nothing upstream

WHILE @intN <= 3500
BEGIN
     SEt @intN = @intN + 1
    INSERT INTO TempTable(LastNode, CurrentNode, N)
      SELECT LastNode, CurrentNode, @intN
      FROM your table
      WHERE LastNode IN (SELECT CurrentNode FROM TempTable WHERE N = @intN-1)

IF @@ROWCOUNT = 0
     BREAK


END

If we assume that every node points to one child. Then this should take no longer than 3500 iterations. If multiple nodes have the same upstream provider then it will take less. But more importantly, this lets you do this...

SELECT LastNode, CurrentNode, N FROM TempTable ORDER BY N

And that will let you see if there are any loops or any other issues with your provider. Incidentally 3500 rows is not that much so even in the worst case of each provider pointing to a different upstream provider, this should not take that long.