[OpenSDI] Image Caching, when to update?

[Josh at oklieb]

The good news is that there are a whole raft of standard HTTP header  
tags for controlling caching, such as "If-Modified-Since". The bad  
news is that most software neither generates nor acts on them at  
present.

-josh

On Aug 4, 2005, at 4:28 PM, Cameron Shorter wrote:

> I've always wondered whether a caching of a WMS/WFS can be  
> controlled by the "Last-Modified" metadata in the HTML response.
>
> For instance, a typical HTML response contains meta data like the  
> following:
>
> HTTP/1.1 200 OK
> Date: Fri, 30 Oct 1998 13:19:41 GMT
> Server: Apache/1.3.3 (Unix)
> Cache-Control: max-age=3600, must-revalidate
> Expires: Fri, 30 Oct 1998 14:19:41 GMT
> Last-Modified: Mon, 29 Jun 1998 02:28:12 GMT
> ETag: "3e86-410-3596fbbc"
> Content-Length: 1040
> Content-Type: text/html
>
> I think image responses contain something similar.
> Proxies usually use the Last-Modified tag to determine whether a  
> cache should be used or not.  I'd suggest that the WFS/WMS should  
> set the Last-Modified flag to the last time the database was updated.
>
> Jody Garnett wrote:
>
>> Chris Holmes wrote:
>>
>>> One thought I've had about this is rigging up extend WFS-T  
>>> functionality
>>> to handle notification and subscriptions.
>>>
>> This is what Galdos does with their "Cascading WFS-T", the  
>> probably initially used it to handle replication between clustered  
>> WFS servers, but once that was in place they pushed it as a way  
>> for clients to be notified of changes.
>> Cheers,
>> Jody
>>
>
> -- 
> Cameron Shorter
> http://cameron.shorter.net
> http://mapbuilder.sourceforge.net
>
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