[AccessD] Design Pointers - Mapping Routes

[David Emerson]

No to A-D because there is no record with A-D or D-A.
Yes to second and third routes.  

-----Original Message-----
From: AccessD <accessd-bounces+newsgrps=dalyn.co.nz at databaseadvisors.com> On
Behalf Of Bill Benson
Sent: Friday, 5 November 2021 12:02 pm
To: Access Developers discussion and problem solving
<accessd at databaseadvisors.com>
Subject: Re: [AccessD] Design Pointers - Mapping Routes

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
>
>
>
>
>
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