# [AccessD] Design Pointers - Mapping Routes

Stuart McLachlan stuart at lexacorp.com.pg
Wed Nov 3 15:53:43 CDT 2021

```"Graph Theory"
https://en.wikipedia.org/wiki/Graph_theory

:)

--
Stuart

On 4 Nov 2021 at 9:22, David Emerson wrote:

> Hi Listers,
>
> A table storing travel routes has fields for two points.  Data might
> look like this:
>
> Point 1		Point 2
> A		B
> A		C
> B		C
> B		D
> C		D
> C		E
> E		D
>
> As can be seen from the last record, the order of the point data may
> not be lowest/highest (it would be easier if the record could be
> entered as D/E but this is not the case).  There will however only be
> one combination of points (eg since there is a record for E/D there
> cannot be a record entered for D/E).
>
> Questions to be answered from the data could be:
> 1) What are the possible routes from A to C (without covering the same
> section twice)? Answers: A-B, B-C A-C
>
> 2) What are the possible routes from A to D (without covering the same
> section twice)? Answers: A-B, B-C, C-D A-B, B-C, C-E, E-D A-B, B-D
>
> 3) What are the possible routes from A to E (without covering the same
> section twice)? Answers: A-B, B-C, C-D, D-E (note that D-E is the E/D
> record) A-B, B-C, C-E A-B, B-D, D-E (note that D-E is the E/D record)
> A-C, C-D, D-E (note that D-E is the E/D record) A-C, C-E
>
> To get the answers it seems that I will need to use queries to come up
> with the different permutations for each record (eg E/D and D/E) so I
> can get all the matches of end point to start point values (and I
> would also need to check that the same route isn't used more than
> once)
>
> Is there a better table structure to achieve this?
>
> Can anyone point me in the right direction as to any theory behind
> this type of mapping, and any code that might help generate the
> solutions?
>
> Regards
>
> David Emerson
> Dalyn Software Ltd
> Wellington, New Zealand
>
>
>
>
>
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