[postgis-users] Data Versioning?

[Craig Miller]

I would just like to chime in that there is a distinct difference between a
spatio-temporal database and database versioning.  Chris outlines a number
of great examples of spatio-temporal database requirements which would all
be wonderful to have.  I almost responded with an identical post as his
yesterday.  I realized that being able to "version" or create a branch of
the content where one can explore "what if" scenarios with spatial data is
not the same thing as capturing spatial data lifeline information.

Versioning support is more inline with CVS.  A good implementation probably
requires a wrapper around the database and a schema to support it.  If done
cleanly, I would imagine that a spatio-temporal schema could then be layered
on top of that.  This is very interesting... Now I am thinking about writing
an SDE for PostGIS!

--Craig


----- Original Message ----- 
From: <chodgson at refractions.net>
To: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
Sent: July 10, 2003 9:52 AM
Subject: RE: [postgis-users] Data Versioning?


> > I would do this versioning in the database though with a before trigger
on
> > the spatial table that on insert/update/or delete copies the prior
version
> > of the record into the meta table.
>
> At first, this sounds like a nice solution - but there are some use cases
which
> cause problems with this sort of "automatic" historical tracking.
>
> It might be the case that you want the "retired" or "deleted" date in the
> database to correspond with the actual date the corresponding real-life
> geographical feature changed, not the date and time that it was updated in
the
> database. Along the same lines, you might also want to go back and update
your
> history to show something that you now know to be true, which was
previously in
> error - this change wouldn't affect the "current" data at all.
>
> To go even further, perhaps you want to track the changes to the
historical
> data - there was a presentation this at the Mapserver user meeting. That
is, so
> that you are able to ask questions like:
>
> What did we think this road looked like in 1991, when we were in 1995?
> What do we think it looked like in 1991, now?
> What do we think the road looks like today?
>
> The key is that you are separately tracking differences due to actual
re-paving
> of the road, and due to corrections in digitizing errors. Perhaps the
first
> thing you should think about when starting to develop a geographic data
> versioning system should be defining what changes you are tracking -
real-life
> changes to the actual geographic features, or just updates to the digital
> model - or both.
>
> Either way, the solution can be as simple as just adding a created date
and
> deleted date to the table, and the code to support the updates to those
fields.
>
> Chris
>
>
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users