October 27, 2016 at 8:35 am #2810tringo335Participant
I have been having some major trouble with diagraming these rules. I found a post by another user who was having the same issues and perfectly explained why:
“I’m suddenly encountering some issues — specifically, complex “or” rules. I’m consistently using a different notation for about half of the questions, and I can tell that I’m misunderstanding the underlying logic, but I’m not sure why. Basically, it seems like I keep wanting to diagram: “A-B-C or C-B-A” for rules that should be diagrammed using diagonal lines. like this:
A \ / A
B or B
C / \ C
I’m not sure how to get this into my head or why/how I’m approaching these questions wrong. I guess the key is that I’m just not understanding how these “diagonal line” diagrams are logically different than simply drawing out “A-B-C or C-B-A.”
Can someone assist with explaining this? As the user stated above, I also don’t really see a difference in using the diagonal diagram vs. the horizontal diagram. Is there really a difference? Or is it just preference? I want to try and understand fully before moving forward. Any help would be great!
October 28, 2016 at 12:15 pm #2811Mike KimKeymaster
Hi Tristan —
Happy to try and help —
If you saw that other post, I imagine you also saw my response to it — but in case you didn’t, here’s a link and maybe some of that will help —
In terms of the specific q you brought up —
wanting to draw something with the horizontal vs with the diagonals —
let’s try and break down exactly what that means —
There are two distinct parts of understanding the issue correctly:
When you have a rule represented:
“A -B – C”
what that means, specifically, about the order of those three elements, is that
A must go before B, which then must go before C.
When you have a rule represented:
“A with two diagonals to the right, one going to B, and one going to C”
what that means, specifically, is that
A is before both B and C, but we don’t know the order of B and C relative to one another.
That’s the basic and fundamental difference between those two notations.
So, if you got the rule “B is after A but before C” it would be correct to diagram it A – B – C
But if you got the rule “A is before both B and C” it would be incorrect to draw A – B – C..
Instead, you’d want to draw both B and C to the right of A, and that’s where the diagonal lines come into play.
Okay, so that’s the first key — and that’s the fundamental difference between notation that goes all in an order and the one with diagonals.
The second concern is the “or” issue — so, if we are told:
“These three elements, A, B, and C, must be ordered in one of just two possible ways.
One way these three elements can be ordered is that A is after both B and C.
And the other way these elements an be ordered is that A is before both B and C.”
So, the first option would cause us to draw both B and C to the left of A —
and the second option would cause us to draw both B and C to the right of A.
And we’d end up with one of these situations, or the other.
It would be incorrect to represent the situation with a A – B – C linear chain, because again, nothing in the rules told us that B comes before C.
So those are the two separate concerns that add up to these complex or scenarios — I probably end up saying the same thing over and over again in the book and my various responses, but I hope hearing it that way helps clear things up a bit more —
Let me know if you have any follow-up — MK
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