[OSGeodata] Re: [Geotools-devel] On the catalog tutorial
Jody Garnett
jgarnett at refractions.net
Mon Sep 25 22:29:09 EDT 2006
Stefan F. Keller wrote:
>
> Jody,
>
> Could'nt follow all details of your post but you hit one of the core
> problems of modeling geo-information and services, namely
> relationships, especially mutual relationship between these.
>
Yes that is a core problem, but one that is very accessible. I always
get stuck on modeling associations between resources. You have been
correctly pointing out that I miss out on some of this information (like
"source").
>
> To me geo-information and services have a many-to-many relationship.
>
Check.
>
> When there is a containment relationship with data access services
> containing geo-information (which is OK for an API) and a set of
> containers you obviously can compute reverse associations to
> re-establish this many-to-many relationship in a libary behind an API.
>
I am afraid we were not that nice, we simply return a list of handles
that satisfy the query, the set of handles returned will all refer to
the same data. But each handle (as they come from different services)
may offer different abilities (from WFS data access, to WMS service side
portrayal).
>
> As you know, I am trying to reach consensus about a minimal
> information metadata model (to all: I'm still awaiting comments or
> counter proposals to http://tinyurl.com/kfkyv). So I like to give my
> 0.25 pennies to this open problem:
>
Will review now, I am afraid I am some weeks behind in reading email
lists that are not part of my core functions :-)
> Having the use case of minimal metadata exchange - not the API - in
> mind, I'm strongly proposing a containment relationship of
> geo-information containing zero to many data access services (data
> binding protocols).
Nice way to slice it, no argument here. May wish to extend it to refer
to other associated information, so in addition to "data binding
protocols" you can refer to associated "intrinsic" resources, such as
FeatureType, Style and different flavours of metadata.
Sorry if that was not clear:
- my road collection
-- WFS data binding:
http://localhost/geoserver/wfs?REQUEST=GetCapabilities+SERVICE=WFS+VERSION=1.0
-- WMS data binding:
http://localhost/geoserver/wms?REQUEST=GetCapabilities+SERVICE=WMS+VERSION=1.3
-- ISO19115: ... could be an intrinsic entry in GeoNetwork containing
traditional ISO19115 metadata
-- SLD: http://localhost/geoserver/wms?REQUEST=GetStyles+Style=road_style
Aka leave it open so you can go beyond data binding later ..., not the
reference to the original source ISO19115 meta data for applications
that can actually care.
> Consider also the fact that geodata can exist without data access
> services but data access services can't.
We do have some odd balls, Web Processing Service, Feature Portrayal
Service which seem to leave by data chaining alone.
> In addition, I'm making a difference between data access services (as
> mentioned above) and 'services on it's own' like filter or label
> placement services. Here I think there is no solution out yet because
> these 'services on it's own' wouldn't contain associations to specific
> geodata (= data access services) but would try to describe kinds and
> structures of geodata they can process.
Point taken, to translate into OGC OWS speak the services you described
have no "resource type" that they are responsible for managing. This is
why a FeaturePortrayalService is not a subset of WMS, FPS has no
resource it is responsible for managing.
>
> So to me, when looking for the best approach to auto-discover
> and publish geo-information, I'd like to ask the following questions:
>
> * What's easier for webcrawlers: find data sets (or metadata about it)
> or services?
So far services seem to be easiest, it is what Paul managed to do.
> * What do data providers more likely do (if they do): register data
> sets or metadata about it containing some data access services or
> services (containing many views to data sets)?
So far they seem to grab geoserver, fill in a little bit of information
as they configure it to publish their information.
> * And finally: What is easier to describe in a minimal metadata model:
> data sets or data access services?
Services seem easier, their is simply less information needed to
describe them. When describing data there is a wider range of
information that may be useful (and indeed the usefulness depends on
what client application is trying to answer the question).
Cheers,
Jody
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