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From Giacomo Pati <>
Subject Re: Why is the SourceValidity isValid( SourceValidity newValidity ) method needed?
Date Mon, 15 Nov 2004 19:23:39 GMT
On Mon, 15 Nov 2004, Peter Hunsberger wrote:

> On Mon, 15 Nov 2004 19:45:42 +0100, Carsten Ziegeler
> <> wrote:
>> Peter Hunsberger wrote:
>>> I'm currently reworking our system to add finer grained cache
>>> normalization and I'm a tad confused as to exactly how Cocoon
>>> checks cache validity.  In particular, as the subject line
>>> says, I can't see why the SourceValidity class needs the
>>> capability to check against a new SourceValidity?
> <snip/>
>> This method is required if the source validity can't tell by
>> itself if it is still valid. For example, if the source
>> validity stores a last modification date of a file (an http
>> request etc.), it can't tell by itself if the resource has
>> changed. In this case the new (current) last modification
>> date is required and the implementation of the source validity
>> would check if they are the same or not.
>> We used to use this for our file based validities for example,
>> until someone had the clever idea to store the file object
>> into the source validity. But if you would only store the
>> last modification date, you need this method.
> I'm still confused:
> 1) Why can't the validity itself figure out whatever it needs to know.
> Eg, go look at the file to see if has been modified?

Becasue the SourceValidity is just a Validity not the resource the 
validity is about.

> 2) Who generates the new source validity for the second check?  I
> can't see how sequence of methods would be actually invoked...

Either a client class using/managing a resource or the resource itself.

> Storing all the knowledge the validity needs to determine validity
> within the validity itself seems like the only thing that makes sense?

Well, depends on the POV. The Validity is all about validity checks not 
about producing them.

>> So, in the general this method is imho needed ;)
> I'll take your word for it, perhaps the real question is, if I'm
> implementing a caching generator what do I really need to worry about?

Giacomo Pati
Otego AG, Switzerland -
Orixo, the XML business alliance -

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