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Re: Keeping crawlers up-to-date

From: Richard Cyganiak <richard@cyganiak.de>
Date: Tue, 28 Apr 2009 19:28:09 +0100
Cc: Leigh Dodds <leigh.dodds@talis.com>, Linking Open Data <public-lod@w3.org>, Nicholas J Humfrey <njh@aelius.com>, Patrick Sinclair <metade@gmail.com>
Message-Id: <EC25A347-80F1-4ED9-BF23-D11F8178CBE1@cyganiak.de>
To: Yves Raimond <yves.raimond@gmail.com>
Possibly relevant:

Feed paging and archiving for Atom feeds. Paging is a nice solution to  
the "small window" problem with syndication feeds. The concept might  
be translatable to RSS 1.0.

Although I have to say that I find the idea of pushing RDF updates via  
Atom quite appealing.


On 28 Apr 2009, at 17:01, Yves Raimond wrote:

> Hello!
>> I think the two main options are either to publish a feed containing
>> pointers to changes, or using a messaging system to push out  
>> notifications.
>> Despite the recent discussion around benefits of, say, Jabber or  
>> other
>> mechanisms for pushing out notifications, I think that a more RESTful
>> approach using RSS or Atom feeds might be nicer. Then we can focus  
>> on the
>> resource design, i.e. what kinds of changes do we need to publish.
>> So for example for /programmes it may be sufficient to publish a  
>> set of
>> feeds for new, e.g. brands, episodes, versions, etc. These could be  
>> RSS 1.0
>> and then include additional RDF data as appropriate.
> My only concern about this is that you need to limit the number of
> items in the feed. If you have a sudden burst of activity and the
> crawler just ping the feed at regular intervals, it may miss some
> updates. However, even with 1M updates in a day, with a feed capped to
> 100 items would just need the crawlers to ping the feed about every
> hour and a half. So that's not too bad.
> (Just noticed that Soren's proposal includes pagination of feeds,
> which might solve that problem).
> So yes, I guess it could be done, using RDF feeds e.g.
> http://www.bbc.co.uk/programmes/updates/2009/04/28/brands.rdf etc.
> We'd need to carefully think about the feeds we offer though.
> Cheers!
> y
>> This has the added advantage that a crawler that only wanted to  
>> collect
>> certain information, e.g. about brands, could monitor just the  
>> resource(s)
>> it was interested in. Similarly with careful resource design, the  
>> timing of
>> updates could also be under the control of the crawler, e.g. new  
>> versions in
>> last 12 hours, 24 hours, 7 days (avoiding a massive firehose of  
>> updates).
>> This could be easily done with URIs and avoids having to build that  
>> into the
>> messaging system.
>> Interested to know what you think.
>> Cheers,
>> L.
>> 2009/4/28 Yves Raimond <yves.raimond@gmail.com>
>>> Hello!
>>> I know this issue has been raised during the LOD BOF at WWW 2009,  
>>> but
>>> I don't know if any possible solutions emerged from there.
>>> The problem we are facing is that data on BBC Programmes changes
>>> approximately 50 000 times a day (new/updated
>>> broadcasts/versions/programmes/segments etc.). As we'd like to  
>>> keep a
>>> set of RDF crawlers up-to-date with our information we were  
>>> wondering
>>> how best to ping these. pingthesemanticweb seems like a nice option,
>>> but it needs the crawlers to ping it often enough to make sure they
>>> didn't miss a change. Another solution we were thinking of would  
>>> be to
>>> stick either Talis changesets [1] or SPARQL/Update statements in a
>>> message queue, which would then be consumed by the crawlers.
>>> Did anyone tried to tackle this problem already?
>>> Cheers!
>>> y
>>> [1] http://n2.talis.com/wiki/Changeset
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>> --
>> Leigh Dodds
>> Programme Manager, Talis Platform
>> Talis
>> leigh.dodds@talis.com
>> http://www.talis.com
Received on Tuesday, 28 April 2009 18:28:54 UTC

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