Yeah, I wouldn't worry too much about this requirement, I've been
thinking about it a bit and I think we could do some decent stuff at the
datastore level. Like a caching datastore could just take two other
datstores - the source (likely a wfs or some other remote one) and the
local.
The goal of caching WFS would be to be able to make use of different
strategies that are particular to a WFS. Things like the
geosynchronization work, which is looking like it'd be a georss feed
notifying on what has changed, or leveraging http cache control headers
(though this won't so much work with wfs, needs an atom type thing). Or
client controlled caching, like expire after a certain amount of time,
or when the user asks for a reload. But yeah, I think we should be able
to design something later that covers several use cases, and could work
with different datastores that might have different ways of notifying
about cache expirations. We can later gather some use cases and make an
informed design.
Chris
Gabriel Roldán wrote:
Hi,
so one requirement for this DataStore is to be "caching friendly".
Yet, though doing some caching strategy specific for it, I've always thought
of a "cached" datastore as a cross-cutting concern, and both Andrea's
original thoughts [1] as well as Christophe Rousson's summer of code work [2]
seem to share that conception.
So I guess I'm not going to do anything in particular to support caching. I
think as long as a DataStore properly implements feature events would be a
good candidate to be wrapped by caching one. It also makes sense for the
client application to decide which of them deserve to be cached and which
not.
Another possibility would be to supply the DataStoreFactory some sort of
implementation hint to, for example, signal the datastore to plug into a SPI
discoverable cache. But, I'm not sure this is a good usage of hints.
thoughts?
Gabriel
[1] <http://docs.codehaus.org/display/GEOTOOLS/Datastore+caching>
[2] <http://docs.codehaus.org/display/GEOTOOLS/SoC+2007+Caching+data>
On Thursday 10 January 2008 06:15:39 pm Jody Garnett wrote:
Gabriel Roldán wrote:
If this seems ok, it'd imply moving some stuff around on the wfs plugin,
mostly some package refactoring to isolate version specific code from
general one. In my opinion it shouldn't be a problem as its the DataStore
nature not to be API, and the only public class should be the datastore
factory.
This is the same approach we took for OWS-3 you can find an example of
how to subclass WFS1.0 datastore
and override just enough methods for GML3 parsing.
The code is still available in svn here:
- http://svn.geotools.org/udig/branches/ows3/gt/owswfs/
While you are there see if you can make a public method for
getCapabilities() it is one of the main reasons we still
subclass WFSDataStore in uDig :-)
This may be obvious but the approach to take is make a strictly 1.0
datastore and a 1.1 specific datastore and let the
WFSDataStoreFactory do the version negotiation in order to choose the
correct version. You will find ShapefileDataStoreFactory
takes the same approach when choosing between ShapefileDataStore and
IndexedShapefileDataStore.
Cheers,
Jody
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