Hi,
I want to add my 2 cents (all AFAIK):
WFS is a standard for data exchange as has been pointed out by
Alessandro already. The data are in an XML format (GML) which is _slow_
compared to data from a database for several reasons. QGIS downloads the
complete layer as GML which, depending on the amount of datasets, can be
huge. There is no spatial index helping QGIS in rendering. Using a layer
from a database is fast because - assuming you created a spatial index -
QGIS only loads the data needed for the particular part of the map you
are currently viewing.
AFAIU you are running different database systems in you network (or
different instances of the same system or different databases on one
system). Depending on the amount of layers e.g. PostreSQL's concept of
foreign data wrappers might be a solution (I do not know anything about
performance though) enabling you to bundle all your layers in one
PostgreSQL database.
Apart from the technical perspective: If you have e.g. several hundred
layers you will always face the problem of how users know where to find
a particular layer, even if theses layers are all in the same database
(same would be true for several hundred WFS layers on one server btw).
In this case you will always need some kind of metadata system where
users can search for data and that tells them how they can access them.
regards
Bernhard
Am 06.01.2021 um 16:48 schrieb Paul Wittle:
Hi Alessandro,
I guess the key is ease of data discovery. So if all your geodata is on one
database then it is all easy enough but if you have multiple database types /
instances then you are relying a lot on users being able to find the right
database / instance and then having potentially different login mechanisms for
each database.
This is why the idea of WFS seems appealing because we can authenticate at
access to the WFS server using a single method; expose all the accessible
datasets in a single list and in theory potentially employ greater consistency
to the method of updates.
We have found that the SQL issued by each database driver can vary in terms of
the SQL optimisation because each one is developed independently of others
(i.e. the Oracle data access is not necessary developed with much reference to
the Postgres or SQL database data access clients). Whilst fundamentally the SQL
statements are still in effect translated into the appropriate SQL for each
database type the original statement should in theory be more consistent?
In terms of speed; I suspect you are definitely correct hence my asking the
question really.
The comments above are really to simply flesh out the question as to whether or
not using a database is really simpler though.
That said; we may also use something like a custom plugin or GeoNetwork as a
data discovery tool which is another way of helping users add the right layer
without needing to know which database it comes from.
I hope that clarifies the question a little better?
Cheers,
Paul
-----Original Message-----
From: Alessandro Pasotti <[email protected]>
Sent: 06 January 2021 15:11
To: Paul Wittle <[email protected]>
Cc: [email protected]
Subject: Re: [Qgis-user] Best practice, database vs WFS
Hi Paul,
if you want to share geodata within your organization on a private network a
database is the best solution: faster and simpler. The constraint is that you
will need an application (like QGIS) to access your data..
WFS is a web service standard for interoperability, it is ideal for sharing
data on the internet over HTTP, there is no need for a particular application
to use the service: any HTTP client is able to do that.
Regards
On Wed, Jan 6, 2021 at 3:43 PM Paul Wittle <[email protected]>
wrote:
Hi,
As I’m sure is clear from the number of posts I’ve done of late we are
currently looking at how we use QGIS within our business. I thought I’d ask a
question here to see if others are considering it as I can’t find too much chat
online about it but I wondered if perhaps there should be some.
We have concluded that in theory the WFS and WFS-T protocols are an OGC
standard (https://www.ogc.org/standards/wfs) and that using an OGC compliant
server they can be used to front various data source formats; i.e. Postgres,
Oracle, SQL Server etc. In theory that means that if you use WFS and WFS-T in
QGIS it should mean that user experience becomes more consistent for the people
using those layers in QGIS.
That all sounds great, but I can’t seem to even get my WFS to load correctly in
QGIS at present and it doesn’t seem to be something that is recommended online.
Given that both WFS and direct database access both return full details (vector
geometries and attributes) to QGIS; would you expect performance of WFS to be
similar or significantly slower?
Is the use of OGC compliant WFS something that you personally feel is something
we should be aspiring to use more widely at the local / network level in QGIS
or do you favour just loading directly from databases?
I’m honestly very interested to hear what others think on this as theoretically
you would think the creation of an OGC standard would have this sort of
aspiration but I’m increasingly concluding that this kind of use of WFS is very
limited. It seems to me that the most common use case is just for occasional
layers where you need to work with others over the internet.
To ensure we are talking about the same thing; I’m thinking that the access to
WFS in this context would be locally within your own network or device as
clearly going over the internet will add a significant overhead and potential
for delay.
Feel free to message me back directly or message the group if you think it is a
worthwhile discussion but as I say I’d love to hear what others think.
Cheers,
Paul
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