[AccessD] Design Pointers - Mapping Routes

[Bill Benson]

Does 2 also contain
A-D
A-C ,C- D
A-C, C-B, B-D

?

On Wed, Nov 3, 2021 at 4:22 PM David Emerson <newsgrps at dalyn.co.nz> 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
>
>
>
>
>
> --
> AccessD mailing list
> AccessD at databaseadvisors.com
> https://databaseadvisors.com/mailman/listinfo/accessd
> Website: http://www.databaseadvisors.com
>