[postgis-users] Data Versioning?

[Chris G. Nicholas]

A few years back, we had a lot of discussion at OpenGIS mtgs about "long transactions."  I personally walked away from these talks feeling it was pretty much the same set of issues CVS grapples with, except on a per-row basis for feature tables.

The typical scenario occurs where several technicians are trying to update/edit an entire coverage and can't "lock" the entire table, the most basic reason that  others need to be able to redraw their screens.  So they do "long transactions" - i.e. check out an entire copy, make their edits, and perform some form of a "merge" operation later on. 

In practice, this sort of thing has far more to do with careful database design and organizational procedure(s) than any catch-all 'feature' in the spatial database. The most basic questions, for this or any other enterprise workflow, come to bear: Who is authorized to make such edits? What is the source data for the  updates; orthophotography?  If so, what scene/frame/date was the image, and what client software was used?  etc. etc. etc.

Chris Nicholas
GlobeXplorer

-----Original Message-----
From:	Jeff McKenna [mailto:mckenna at dmsolutions.ca]
Sent:	Mon 7/14/2003 5:45 AM
To:	PostGIS Users Discussion
Cc:	
Subject:	Re: [postgis-users] Data Versioning?
Thank you everyone for your replies to my spatial versioning question. 
It's given me lots to think about.  cya.


Jeff




Paul Ramsey wrote:
> Hi Jeff,
> I'll just finish off the Refractions tag-teaming of you :)
>   I am writing from the Heart of Darkness itself, the ESRI UC, so I know 
> whereof I speak, when I say: Jeff, free your mind! Do not confuse the 
> particular terminology and implementation of a vendor with the application 
> of a broader concept. ArcSDE versioning is a particular application of a 
> form of spatio-temporal database schema. But it is not the only possible 
> application, and it may not fit the needs of every user -- Chris has given 
> some examples of change tracking which go well beyond the ArcSDE paradigm, 
> but which *can* be supported through a well designed database schema.
>   Remember, at root, all that ArcSDE "versioning" is, is a particular schema 
> implemented in the RDBMS, and managed via the ArcSDE middleware. You can go 
> into your ArcSDE geodatabase and interrogate the tables, see how they 
> modelled the particular problem.
>   Here in the Heart of Darkness, it is easy to forget that GIS transcends 
> the particular boundaries and terminology used by ESRI, but it does.
> Yours,
> Paul
> 
> 
> Quoting Jeff McKenna <mckenna at dmsolutions.ca>:
> 
> 
>>I guess I was hoping to hear that PostGIS/PostgreSQL already handled
>>spatial data versioning similar to ArcSDE.
>>I understand the concept of 'meta tables' storing extra timestamp info,
>>but are there examples of this already in use out there?  Has anyone
>>been successful in implementing spatial data versioning with
>>PostGIS/PostgreSQL????  (we deal with large datasets and this would
>>impact the way we do things bigtime)
>>
>>thanks.
>>
> 
> 
> 
> 
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> 


-- 
Jeff McKenna
GIS Specialist
DM Solutions Group Inc.
http://www.dmsolutions.ca


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