[Mapserver-users] SDE Direct Connect

[Steve Lime]

Regarding 4, which functions are those? I wasn't able to  find any
references to direct connect in my admittedly outdated SDE C API
documentation.

Steve

>>> <Michael.Smith at erdc.usace.army.mil> 12/11/2003 12:45:52 PM >>>
There is some errors is here that I have to correct.

1. Oracle does indeed have direct spatial support but that is not
necessarily incompatitble with SDE. SDE can store data in sdebinary
format,
longraw format (which is being deprecated I belive) and native Oracle
Spatial format. 

2. Direct connect actually has nothing to do with how SDE stores
information. SDE can operate in two modes. Standard or 3 tier mode, in
which
the client connects to an SDE server which will then communicate with
the
database. Or Direct Connect or 2 tier mode, in which some of abilities
of
the sde server are done in the client. ArcGIS can operate this way. The
part
of SDE that communicates with the database in built in to ArcGIS to do
this.
Mapserver still doesn't have to know anything about Oracle Spatial as
that
is all part of the direct connect code built into the client. However,
the
client abilities are limited in that it is a read only connection, even
if
you have an sde license. 

3. I wouldn't say that SDE 3 tier is slower than 2 tier. As with so
many
things, it depends.

4. The C Api that mapserver links to does support direct connect
however I
don't believe that the direct connection functions have been
implemented

Here what Esri says about Direct Connect

Direct Connect is a method for ArcSDE client applications to connect
directly to the spatial database (hosted on either Oracle 8i or
Microsoft
SQL Server) without having to use the ArcSDE application server. 

The classic ArcSDE connection architecture is three-tiered, it includes
an
application server process (giomgr), a per-connection server process
(gsrvr), and a client application. ESRI client applications include
ArcGIS
Desktop and ArcView. Within this architecture, the ArcSDE giomgr
process
manages connections from client applications. When a connection to
Oracle8i
is granted through the giomgr process, a gsrvr process is spawned to
service
the new connection. The gsrvr process manages all subsequent query
operations between the client application and the RDBMS for the
duration of
the connection. Both the giomgr process and gsrvr process exist on the
server machine that hosts ArcSDE and (usually) Oracle. 

Direct-connect is a two-tiered architecture, wherein ArcSDE client
applications can connect directly to an Oracle8i instance. The
functionality
of the gsrvr process has been added to a set of libraries used directly
by
ArcSDE clients. Typically, ArcSDE clients run on remote desktop
machines,
while the Oracle8i instance runs on a server-class machine. The
functions of
the gsrvr process become part of the client application running on the
client machine. The ArcSDE giomgr process (part of the three-tiered
architecture) is not used to manage direct-connect connections, though
it
can continue to be used for three-tiered client connections
simultaneously
with two-tiered direct-connect client connections. 

-----Original Message-----
From: Charles Greer [mailto:CGREER at sonoma-county.org] 
Sent: Thursday, December 11, 2003 12:16 PM
To: godwinl at agr.gc.ca; Jean-Francois.Doyon at CCRS.NRCan.gc.ca;
mapserver-users at lists.gis.umn.edu 
Subject: RE: [Mapserver-users] SDE Direct Connect


I've been following this list for some time now, eager to do more
MapServer
development and to contribute to the discussion, but for the time being
all
my time is taken up by things like SDE and ArcIMS, 
so now I've got the opportunity to clarify the issues a little bit. 
Caveat
- I'm a DB2 spatial guy 
and don't know Oracle I've become more familiar over time with the
bizarre
issues surrounding Oracle and spatial stuff, so...

Oracle has inherent spatial support that is in many ways incompatible
with
the way that SDE handles things.  In fact, spatial types in "ArcSDE
with
Oracle" are simply BLOBS, whereas the "direct connect" method supports
Oracle's native geometric/geographic types.  The creation of a "direct
connect" for Oracle was ESRI's response to the inherent
incompatability
between how Oracle Spatial and ArcSDE handle things.

In other words, direct connect is a way to bypass SDE.  Thus as J.F.
says
below MapServer would have to know a lot more about native Oracle
Spatial
support in order to support the sde:oracle method.  That's also why,
for
Oracle, SDE is 
slower than direct connect in many applications.

ArcSDE is a "lowest common denominator" API, which supports geographic
types
even when the underlying RDBMS doesn't (like SQL Server, or the base
Oracle
product).  
So its a good API to deliver geography to MapServer, but will not take
advantage of all the 
full range of spatial features in any of the spatial databases.

I hope that helps with the discussion somewhat.  Hope to participate
more
fully in the future,

Charles Greer


>>> <Jean-Francois.Doyon at CCRS.NRCan.gc.ca> 12/11/03 08:53AM >>>
Liz,

The Arc clients do provide that flexibility, though I don't think you
can do
that right now with MapServer.

The main problem is that the underlying organization of data (i.e. SDE
table
structure) doesn't lend itself to that kind of access without the
client
explicitly understanding it, which mapserver natively wouldn't ...

If you really wanted you could do something like use PHP/MapScript to
read
the data directly out of Oracle, and then put it into a format
MapScript
understands and so on, but that's probably much slower than just using
the
SDE service !!

As a general rule MapServer's SDE support is fairly basic ... It only
reads
basic tables and so on ... If for example you use more advanced
features
such as geodatabases, you can no longer really use MapServer with SDE
(That's what I was told by someone who looked at that at least ...)

As a general idea it might be nice to look at expanding MapServer
support
for SDE to be more aware of some SDE specific features, such as
GeoDatabases
and the direct connect feature ... We'd have to find out whether the
latest
Client SDK provides the necessary functionality and look at adding
mapserver
support for it.  What you've found about "sde:oracle" suggests that at
least
part of the funcitonality is probably there, but mapserver doesn't work
with
it nicely ...

But I'm pretty sure the short answer right now is that you can't do it
:)

J.F.

-----Original Message-----
From: mapserver-users-admin at lists.gis.umn.edu 
[mailto:mapserver-users-admin at lists.gis.umn.edu]On Behalf Of Liz
Godwin
Sent: Thursday, December 11, 2003 11:24 AM
To: mapserver-users at lists.gis.umn.edu 
Subject: [Mapserver-users] SDE Direct Connect


Hello,

Is it possible to connect directly to SDE through mapserver, or only to
the
the sde service?  I have tried playing with the connection string in my
map
file, but to no avail.  

I have heard that a direct connection is faster than a service
connection,
that is why I would like to try this.

In the SDE config/tuning guide for Oracle, it suggests I use
"sde:oracle" as
my service, instead of "esri_sde " for a direct connection. My
connection
string in my map file: 
"<hostname>,sde:oracle,<database>,<user>,<password>"  (all
<parameters>
filled in) My error:  msSDELayerOpen(): SDE error.
SE_connection_create():
The file path does not exist, or is too long (> 512 chars), or has
invalid
characters.. (-269)

This error suggests to me that the SDE handler in Mapserver doesn't
like the
colon.  Is this a bug, or is it just not possible for a direct
connection?

Thanks!!

Liz Godwin



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