[Freegis-list] Clearinghouse

[Felipe Nievinski]

Hi.

On Mon, 01 Apr 2002, John Reid wrote:
> I'm currently looking at setting up a demo dataset using freely
> available datasets for my local area, concentrating initially on storage
> of data catalogues and metadata.

John,
I just read your message. The message below is in response to Alexander's message.
The idea of the addition to the SDI Cookbook is great. I'll get back to you asap.


On Tue, Mar 26, 2002, Alexander Pucher wrote:
> I'm recently planning to set up an geodata clearinghouse using free
> software. Right now, all data is stored in an ArcGIS personal
> geodatabase. I've searched the web and found some stuff from the FGDC
> (mainly the Isite package).

By clearinghouse I understand a decentralized system of servers
full of metadata in a networked environment, used for resource
discovery.

The Z39.50 protocol is widely used for communication between
computers in a clearinghouse. Isite is a package of (free
software) programs for distributed searching. It contains a
Z39.50 server implementation, besides other things.

By using Isite you can:
- index a file collection, each file being a metadata record,
- search locally this database,
- receive queries via Z39.50.

If you just want to create and add a server peer to an existing
clearinghouse (for example, registry.gsdi.org) this is almost
all you'll need to do. You can then notify the clearinghouse
maintainer that your server is ready to be accessed, and
perform queries on local or remote Z39.50 servers using a
Z39.50 client or through an already available http to Z39.50
gateway.

To manage your metadata file collection (create, update and
delete records), do it by hand offline, or build a web-based
system using your prefered language. There is available (see
URL below) a set of very elucidative Perl scripts which makes
a metadata entry system.
Any modification to your metadata-base you'll have to re-index
it and restart the Z server.

If you also want to build your own http to z39.50 gateway, be
prepared to dig deep. As far as I can tell you, the Isite zcon
defines the presentation of the search results (the way it
formats Z39.50 responses into HTML) in its source code, so
you'll have to hack its internals just to add your
university logo to the results page, for example.
Maybe the PHPYAZ (again, see URL below), a Z39.50 client
for PHP, can do a better job.

If you want to serve the actual data online, provide links for
it in the metadata records (the metadata standards usually
define linkage fields to provide this information). Look at a (free)
Web Map Service server or a Web Feature Server if you want
to provide dynamic content rather than just static files.

Just some ideas.
Commentaries are welcomed.

The URLs:
- Isite 2.05 - General Instructions
  http://www.awcubed.com/Isite/FGDC-README.html
- Web-based FGDC Metadata Entry System
  http://130.11.52.178/metaover.html
- PHPYAZ
  http://www.indexdata.dk/phpyaz/
- Spatial Data Infrastrucures Implementation Guide
  Chapter Four: Geospatial Data Catalog -- Making data discoverable
  http://www.gsdi.org/pubs/cookbook/cookbook0515.pdf

regards,
Felipe N.