distributed data

[Stephen Lime]

The balancing script I sent assumed mirrored machines where a full map
would be composed on a single machine. Balancing takes place in choosing
which machine to use.

There are a couple of interesting possibilities dealing with distributed data. One
is a technology called OGDI (Open Geographic Data Interface - I think) developed
in Canada. Simliar in concept to ODBI for relational databases it allows clients to
retrieve data, in a structured manner, from spatial data servers. These servers
use datatype drivers (eg. shapefile, mif, dxf, etc...) to return *raw* data to the
client. It's possible that the MapServer could be a OGDI client and that remote
data could be incorporated into any map. Mechanism would be easy, instead of
refering to a local data file (using DATA keyword) you'd refer to a remote resource
using the OGDI gltp protocol. For more info, see http://www.ogdi.org/.

A second possibilty would be working within the framework being developed by the
OpenGIS Consortium "Web Mapping Testbed". I haven't read much on this yet
and there are several MapServer users who are a part of this that can comment
better than I. One concept they've put forth is a "cascading" map server where
gifs from multiple map engines would be composited and returned to the client. 
MapServer could pretty easily become WMT compliant and could serve GIFs. There
are questions as to symbology and annotation that would need to be addressed.
See www.opengis.org for more info.

Steve

Stephen Lime
Internet Applications Analyst
MIS Bureau - MN DNR

(651) 297-2937
steve.lime at dnr.state.mn.us

>>> "Grzegorz Myrda" <mapadm at polsl.gliwice.pl> 09/23 5:22 PM >>>
Some weeks ago Steven wrote something about balancing.
May it be used to make a map from shapefiles located at different servers
(each with mapserv), on joining GIFs (as layers) from 2 (or more) servers
basis?

Grzegorz