Re: wish: could composite store info about datastores that have been changed?

Axel Hecht wrote:
> Marja wrote:
> 
>> I wrote code that updates datastore changes to Web too. I'm using 
>> several composite stores for different purposes. One composite is for 
>> reading (because that you can do from the Web directly) and some 
>> others for writing and updating. However, as far as I understand the 
>> composite does in no way support finding out which stores included in 
>> the composite need refreshing e.g. which stores in the composite 
>> changed when I asserted something.
> 
> 
> Asserting into a composite DS is considered harmful. I strongly suggest 
> that you directly put your arcs into the datasource they should go to.

I realized that after some experimenting, but why then offer that 
interface? Or at least document this warning anywhere with the interface?

And actually the documentation for which store is written to in a 
composite is wrong anyways: I think the documentation says write to last 
one but it actually writes to the first one or vice versa. But that does 
not really matter because there was no way to control that something was 
last or first if the store was already in the list.

I still try to use composites, but now several of them for different 
reading, writing, and updating purposes as I thought they would offer 
some benefits, e.g. be able to have store assertions etc. to a default 
store if the others did not work and keep track of things so I can just 
give one object to observers. But the composite does not give much help 
for anything.
> 
>> Would it be possible to keep track and tell which one of stores in the 
>> composite need refreshing after the composite RDF was modified by 
>> doing assertions, modifications etc. to the composite? This would help 
>> to optimize some Web traffic.
> 
> 
> This optimization should be handled by the datasource itself. Just make 
> it store a dirty flag. There is no need to do this in the composite DS.

I could not find a dirty flag interface for datasource:
http://xulplanet.com/references/xpcomref/comps/c_rdfdatasource1namexmldatasource.html

I guess you mean I keep track of changed datasources myself and hope I'm 
in right context after all the observations when I finally need to 
refresh to have the updated info. (I think the context actually works in 
and out when systematically using openDialog parameters for it but it 
would be so nice to do it in a simpler way.)
> 
>> I understand that when I use http to upload something to Web it may be 
>> difficult to find that out but if I know which stores were written 
>> locally with RDF store APIs I can keep track of the Web modifications 
>> and save some unnecessary Web reading and uploading.
>>
>> Naturally it would also help if composites and other datastores would 
>> do the uploading in the Web without my code. But that is a bit more 
>> work. Has someone done this already as a package?
> 
> 
> How do you upload?

I have tried different ways for HTTP both read and write. Now I use 
nsIUploadChannel and stream for upload, unfortunately my operator does 
not accept HTTP so testing has been not so easy but I did manage to do 
some in another site. I think adding ftp should be easy now too but 
haven't done it yet.

I also use XMLHttpRequest for GET to read stuff from Web to temporary 
local files so that I can use remote datasource RDF API for updating. I 
also wrote XMLHttpRequest code for POST and PUT but haven't tested that 
thoroughly only parts. I'm not sure anymore if authentication was done 
automatically with XMLHttpRequest or if I should do something similar 
I'm doing with uploadChannel and nsIAuthPrompt but coudn't figure out how.

I did try nsIDownload and WebBrowserPersist too for downloading but 
there were some problems in writing the loaded stuff to a local file so 
I finally gave up on it.

I'll do some more testing (maybe need my own http server) and then hope 
to be able to put the code to CVS (and then try to optimize it better).

Marja
(some day hoping to get back on focusing on semantic Web and social 
bookmark/annotation user interfaces and not on protocols :-) )

> 
> Axel