[fdo-internals] Standardising FDO Schema's

Wed Sep 3 09:57:33 EDT 2008

Haris,

Well I think the layer is less tightly linked to MapGuide then you might think. If you look at AutoCAD Map, we have the same API and a lot of shared code with MapGuide. We sometimes call it the Platform API and use it within Autodesk to do things similarly as to what you describe. In fact I keep encouraging people to use these platform API's more and it is what we build our applications on. You will find the projects files to create a lean version of the core API's to be part of the mapguide source stream.

The biggest problem I think is that we would need an open source version that is an AutoCAD and MapGuide independent implementation of the resource service and feature service. The other API's including coordinate system are already pretty independent. We have not done that yet so it is not free but it is what I would recommend to this group if we were to entertain the creation of an "FDO application layer" ...

Cheers,
  Carsten

-----Original Message-----
From: fdo-internals-bounces at lists.osgeo.org [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Haris Kurtagic
Sent: Wednesday, September 03, 2008 8:28 AM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] Standardising FDO Schema's

Carsten,
I think yes, but layer tightly coupled with Mapguide. Some of those
functionalities I see in FDO application layer.

One of things I would like to point out is that in my opinion FDO
providers need to be very light, without extra layers (being too smart,
sorry don't know how to say it in English).

For example, I am thinking to add functionality to FDO KML provider to
allow to write data from different coordinate systems. So you can write
any CS data to KML.
Most probably , right now way to do it is to take some code from MG
feature services ( I hope a lot :) ) and put it inside FDO provider.
That is no way I would like to do it , not even if it is shared library
to use. I would rather do it in "FDO application layer".

Haris

-----Original Message-----
From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Carsten Hess
Sent: Wednesday, September 03, 2008 1:49 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] Standardising FDO Schema's

Haris,

I wonder ... do you thinkt he MG resource service and feature service
are just that, an application layer on top of FDO? At least that is how
I think of the MG service API's quite often ...

Cheers,
  Carsten
________________________________
From: fdo-internals-bounces at lists.osgeo.org
[fdo-internals-bounces at lists.osgeo.org] On Behalf Of Haris Kurtagic
[haris at sl-king.com]
Sent: Wednesday, September 03, 2008 6:40 AM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] Standardising FDO Schema's

Hi Orest,

I would like to add my point here. I think naming or adding db schema
name or column name to FDO class name doesn't have anything to do with
FDO capabilities, architecture, etc... Such method was choosed to get
unique FDO class name, nothing more. Name could be any kind of random
generated character string (while it is unique inside schema).
As you said FDO class supports many geometry columns as properties and
has main geometry property. As far as I can remember it doesn't work
well with client like MG. I can't remember all issue I had, I think one
of them was spatial context. To fully support "choose any geometry
property" concept then it should not be main geometry property for FDO
class.

I run into this naming problems across providers while writing Fdo2Fdo
as well as providers.
For Oracle provider we have metadata table for KML it is configuration
file.

My thinking was that solution would be (again) FDO application layer. In
that middle level between application and provider such name overrides
would occur.

Haris

From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Orest
Halustchak
Sent: Tuesday, September 02, 2008 10:15 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] Standardising FDO Schema's

Hi,

I don't have a problem with defining some simple conventions such as a
default schema name if one isn't specified explicitly, especially if
it's a generic issue.

However, regarding the geometry property example in the discussion where
'~GeomColName' is appended to the class name, there is another approach.
FDO allows for more than one geometry property in a class. There is one
that is tagged as the main geometry, but there can be others in the
class. It's not a common case, but I have seen examples where additional
geometry properties provide additional information for label points,
schematics, or other things. So, it is valid to generate a single
feature class from an rdbms table that has more than one geometry
column. Some providers have chosen to generate separate feature classes
with only one geometry property per class. In some ways, that is easier
for a client application to deal with, but is not an FDO restriction.
MapGuide Studio, for instance, allows you to choose which geometry
property to use when creating a layer from a feature class definition.

FDO has a component for physical schema overrides that was meant to help
the user with mapping the fdo logical elements with a data stores
physical elements. I suspect that fdo users and developers may not be
finding this that helpful as currently specified. Maybe we need to look
at this in conjunction with the other schema mapping discussions to see
if improving this may help the current issues. The theory was that it
would provide users with a way to add explicit mapping from classes and
properties to physical elements such as tables and columns for rdbms'
and also to be able to identify physical elements from the logical
elements when accessing existing schema. However, because the physical
aspects of data stores are specific to the particular formats, these
overrides were provider-dependent, with provider-dependent api, hence
not easy to use with a general client application. Providers that
supported this override saved the override mapping information in
metadata tables or a configuration file. Finding a more general way to
do this by not using provider specific api's might make this much more
usable. I wonder if anyone has thoughts on this.

Thanks,
Orest.

From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Traian
Stanev
Sent: Friday, August 29, 2008 11:10 PM
To: FDO Internals Mail List
Subject: RE: [fdo-internals] Standardising FDO Schema's

I agree with Robert on this one. There's a schema (or schemas). It has a
name. It has classes. The classes have names. From the point of view of
the FDO client app, those remain consistent within the boundary of the
FDO connection.

If the provider is doing some monkeying around with class names that
come from the source database, it's the provider's job to be consistent
about handling such mangled names. How the provider does that? Who
cares, as long as it does?

Traian

From: fdo-internals-bounces at lists.osgeo.org
[mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Zac Spitzer
Sent: Friday, August 29, 2008 10:54 PM
To: FDO Internals Mail List
Subject: Re: [fdo-internals] Standardising FDO Schema's

On Sat, Aug 30, 2008 at 5:08 AM, Robert Fortin
<robert.fortin at autodesk.com<mailto:robert.fortin at autodesk.com>> wrote:
As Orest said, FDO represents the data in different layer Datastore,
Schema and Class. That's the rule.  That's the standard.
The fact that some provider doesn't have/require schema doesn't mean we
don't need a generic schema representation in FDO.  It's up to the
provider to say what this schema is named and what it maps to (e.g.
default or something else). FDO doesn't impose rules around the name of
the schema.

but currently there is no standard implementation pattern! that's the
problem!
which means every implementation can be different!

should a fdo client really care about which provider and data source is
being used?

Isn't FDO meant to flatten out all these differences...

In Orest's example with the oracle database, the database already
exists, with a well known
and understood access pattern right.  the database supports the use of
grants, synonyms,
roles etc. there is an existing structure in place.

create user denver identified by datamonkey
grant select on parcels.denver to denver.parcels
and so on

Isn't that a much easier and better place to be managing this kind of
thing?
For example, removing the schema from SHP would result that you could
have 2 flavors of shp depending on the connection.  Connect to a single
file and you get no schema.  Connect to a directory and you get a schema
name "default".  SHP provider standardize to using "default" every time.
Also applications relies on that standard: there will be a schema and it
will have a name.  This result in consistant representation of the
schemas and classes in a tree view for example. Changing this behavior
has impacts on applications relying on that standard.

I agree the my suggestion of an empty schema would cause headaches, does
FDO have the concept of
a default schema? Ie GetDefaultSchema()? I just know fdo mostly from the
mapguide api side of things

standardising along these lines, primarily for databases providers,
means that any updating
to support this model would mostly involve removing custom provider
specific workarounds....

A lot of applications wouldn't be affected at all, they just pull
whatever structure the provider represents.

Those which do, probably have a lot of case statements to handle each
different provider's quirks,
which could potentially be deleted.

z

Robert

-----Original Message-----
From:
fdo-internals-bounces at lists.osgeo.org<mailto:fdo-internals-bounces at lists
.osgeo.org>
[mailto:fdo-internals-bounces at lists.osgeo.org<mailto:fdo-internals-bounc
es at lists.osgeo.org>] On Behalf Of Mateusz Loskot
Sent: Friday, August 29, 2008 11:05 AM
To: FDO Internals Mail List
Subject: Re: [fdo-internals] Standardising FDO Schema's

Orest Halustchak wrote:
> [...]
> The above is a logical schema. How could that be mapped to physical
> schema? The discussion started with Oracle. Let's say I have an
> Oracle instance called ORCL. The main physical grouping mechanism
> that Oracle has is an Oracle Owner. So, one mapping is that the FDO
> Data Store maps to Oracle Owner, then FDO Schema.Class maps to table.
> That keeps the integrated set of data within a single Oracle owner.
> Another mapping is to map FDO schema to Oracle Owner, i.e. define
> Oracle owners LANDUSE, TRANSPORTATION, etc. But, then how do we
> separate CityOfDenver parcels from CityOfBoulder parcels? I could
> have DENVER_LANDUSE, BOULDER_LANDUSE, etc. There is a third mapping
> possible, and that's to use a separate Oracle instance for each data
> store, but users may not want to set up separate physical instances
> for this purpose, especially if they have a large number of data
> stores.

Orest,

Thanks for the very in-depth explanation of schema naming issues.

But we still need a consistent way to define and describe all
possibilities of mapping and naming paths in text.
As Zac proves, using only separators (like ::, ~, etc.) is insufficient.

I think more self-describing approach is needed, perhaps we would use
XML or JSON for naming schemas?

Best regards,
--
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org
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--
Zac Spitzer -
http://zacster.blogspot.com (My Blog)
+61 405 847 168
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