[GRASS5] Proposal for a GRASS daemon to deliver metadata

[Roger Bivand]

Hello Justin,

On Tue, 29 Aug 2000, Justin Hickey wrote:
> 
> OK, I think I understand the problem. So, for example, in PostgreSQL, we
> would want to store attribute data corresponding to geographic data in
> GRASS. And to link the two pieces of data we need to also keep track of
> the metadata (location, mapset). Now the question being raised is "How
> to link the two data items using the metadata?" Is this a correct
> analogy of the problem?

Yes, as a subset. I'm not clear myself (as you can see!), but potentially
external programs like R or PostgreSQL can generate new or modified GRASS
data objects themselves, that ought to be related to the location
metadata. So it's potentially not just to link two data items, but maybe
to build an audit trail for data moving in and out of the GRASS database.

> 
> If so, then I still don't understand how a daemon could be used to solve
> this problem. The metadata would still need to be obtained from
> somewhere and sent to the appropriate process that is requesting the
> data. I do not see how the duplication is avoided.
> 
> Could you please indicate how you expect the daemon to operate and how
> the duplication is avoided, in terms of data management? I'm not clear
> on this part.
> 
One possibility would be to ask processes making transactions against the
GRASS database to check them in and out (like CVS?), say in a
database. The daemon idea would be a "middleware" to link the transactions
(what, how, which metadata?) to the database back-ends on the one hand and
application front-ends on the other. A daemon is one way (maybe?), but
it's rather like an object-broker interface too. A daemon would look like
"postmaster", for registering transactions or for retrieving data about
transactions (given that the transaction key is "glued" to the data
object). I know that this isn't too clear, but I'm not sure that it's
entirely fruitless either.

Yours,

Roger

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand at nhh.no
and: Department of Geography and Regional Development, University of
Gdansk, al. Mar. J. Pilsudskiego 46, PL-81 378 Gdynia, Poland.


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