Re: [Neo4j] How to modelize roads with constraints?

[Craig Taverner]

Here's an idea:

Model intersection nodes like B as as a set of entry/exit points to the intersection. In your case there would be three such nodes, BA, BC and BD, each representing the entry/exit to the road to destinations A, C and D. The relationships between the different nodes of B would all be of a different type than the road relationships. Traversing the graph needs a rule that you can never traverse two intersection relationships in a row (cannot drive round and round in the intersection). Then all you need to add is a direction constraint to the intersection relationships, and you will have achieved your goal.

       BC---C

       /|

      / |

 A---BA |

      \ |

       \|

       BD---D

Roads:

• A---BA, bi-directional road
• C---BC, bi-directional road
• D---BD, bi-directional road

Intersection:

• BA---BD, bi-directional
• BA---BC, bi-directional
• BC-->BD, only one direction - you cannot turn from D to C, only from C to D

So, as long as your traversal algorithm respects the direction of the relationships (both road and interesection) and also enforces the rule that you can never traverse two intersection relationships in a row, then you will not be able to take a right turn from D to C through the intersection.

On Tue, Aug 14, 2012 at 10:41 AM, Benoît Lafontaine <joel...@gmail.com> wrote:

Hi,

I have to modelize roads. And I have the following problem

                     /--[Road]-->(C)

                    /

(A)<--[Road]-->(B)<=

                    \

                     \--[Road]-->(D)

A, C and D are points like cities, B is an intersection.

The constraint is that is not allowed to turn to C when you come from D. So you can drive from A to C, from A to D, but you can't drive from D to C.

What's the best way to modelize such graph with this constraint?

Tx