[GRASS5] Proposal for a GRASS daemon to deliver metadata

[Justin Hickey]

Hello Roger

Roger Bivand wrote:
> The reason for the question is that when GRASS data are used by GRASS
> programs in the GRASS environment, they are associated with
> "their" metadata (location, region etc.) through environmental
> variables. When the data are interfaced to R or indeed PostgreSQL, it
> isn't too clear how to maintain consistency between the data and their
> initial metadata, which ought to matter in general, and does matter
> when they move back into the environment used by GRASS programs. In
> the first R/GRASS interface version, all the data moved were tagged
> with their metadata, but this led to lots of duplication. The fact
> that the same question appears to affect PostgreSQL made us feel that
> it is a general one, calling for consideration of how to keep the
> metadata and the data consistent.

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?

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.

-- 
Sincerely,

Jazzman (a.k.a. Justin Hickey)  e-mail: jhickey at hpcc.nectec.or.th
High Performance Computing Center
National Electronics and Computer Technology Center (NECTEC)
Bangkok, Thailand
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