# [postgis-users] Creating a Flow Diagram

Sufficool, Stanley ssufficool at rov.sbcounty.gov
Mon Jun 2 10:06:14 PDT 2008

```Comments below

> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net] On
> Behalf Of Bob Pawley
> Sent: Monday, June 02, 2008 9:30 AM
> To: PostGIS Users Discussion
> Subject: [postgis-users] Creating a Flow Diagram
>
>
> Hi Stanley
>
> I'm still in the primary learning stage with Postgis.
>
> I would appreciate you critiquing my thoughts.
>
> With the two tables - entity and entity_relationship - the idea is to
> establish a parent geometry (perhaps a point known to be
> within established
> boundries) and establish the position of  child entities ( in
> my case,
> process graphics) in relationship to the parent.

That is correct. The entitity table would contain 2d/3d Polygons of your
diagram entities. Points in this table would not work due to st_centroid
in the would-be trigger function. A slight modification would fix this.

>
> Furthermore, you seem to indicate that any entity can be both
> a parent
> and/or a child to another entity.
>

Yes, this allows for one to many relations of parent to child (1-->2 &&
1-->3) and for network diagrams

> You also indicate that the placement of the child entity can
> be established
> in relation to the relative geometric sizes of the entities.
>

Yes, examples:
For a parent entity (1) with a child (2) placed to the right of the
parent, you would have entity_relation (1,2,1,0,0)
For a parent entity (1) with a child (2) placed to the top of the
parent, you would have entity_relation (1,2,0,1,0)
For a parent entity (1) with a child (2) placed to the left of the
parent, you would have entity_relation (1,2,-1,0,0)
*If anyone actually produces a 3d diagram using the ratio_z, this would
be a first in my book and would be very interesting to see.

> Have I been somewhat correct so far?
>
> Bob
>
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```