W3C home > Mailing lists > Public > public-lod@w3.org > June 2011

Re: Think before you write Semantic Web crawlers

From: Jiří Procházka <ojirio@gmail.com>
Date: Wed, 22 Jun 2011 16:03:58 +0200
Message-ID: <4E01F64E.1020703@gmail.com>
To: Martin Hepp <martin.hepp@ebusiness-unibw.org>
CC: public-lod@w3.org
I understand that, but I doubt your conclusion, that those crawlers are
targeting semantic web, since like you said they don't even properly
identify themselves and as far as I know, on Universities also regular
web search and crawling is researched. Maybe lot of them are targeting
semantic web, but we should look at all measures to conserve bandwidth,
from avoiding regular web crawler interest, aiding infrastructure like
Ping the Semantic Web to optimizing delivery and even distribution of
the data among resouces.

Best,
Jiri

On 06/22/2011 03:21 PM, Martin Hepp wrote:
> Thanks, Jiri, but the load comes from academic crawler prototypes firing from broad University infrastructures.
> Best
> Martin
> 
> 
> On Jun 22, 2011, at 12:40 PM, Jiří Procházka wrote:
> 
>> I wonder, are ways to link RDF data so that convential crawlers do not
>> crawl it, but only the semantic web aware ones do?
>> I am not sure how the current practice of linking by link tag in the
>> html headers could cause this, but it may be case that those heavy loads
>> come from a crawlers having nothing to do with semantic web...
>> Maybe we should start linking to our rdf/xml, turtle, ntriples files and
>> publishing sitemap info in RDFa...
>>
>> Best,
>> Jiri
>>
>> On 06/22/2011 09:00 AM, Steve Harris wrote:
>>> While I don't agree with Andreas exactly that it's the site owners fault, this is something that publishers of non-semantic data have to deal with.
>>>
>>> If you publish a large collection of interlinked data which looks interesting to conventional crawlers and is expensive to generate, conventional web crawlers will be all over it. The main difference is that a greater percentage of those are written properly, to follow robots.txt and the guidelines about hit frequency (maximum 1 request per second per domain, no parallel crawling).
>>>
>>> Has someone published similar guidelines for semantic web crawlers?
>>>
>>> The ones that don't behave themselves get banned, either in robots.txt, or explicitly by the server. 
>>>
>>> - Steve
>>>
>>> On 2011-06-22, at 06:07, Martin Hepp wrote:
>>>
>>>> Hi Daniel,
>>>> Thanks for the link! I will relay this to relevant site-owners.
>>>>
>>>> However, I still challenge Andreas' statement that the site-owners are to blame for publishing large amounts of data on small servers.
>>>>
>>>> One can publish 10,000 PDF documents on a tiny server without being hit by DoS-style crazy crawlers. Why should the same not hold if I publish RDF?
>>>>
>>>> But for sure, it is necessary to advise all publishers of large RDF datasets to protect themselves against hungry crawlers and actual DoS attacks.
>>>>
>>>> Imagine if a large site was brought down by a botnet that is exploiting Semantic Sitemap information for DoS attacks, focussing on the large dump files. 
>>>> This could end LOD experiments for that site.
>>>>
>>>>
>>>> Best
>>>>
>>>> Martin
>>>>
>>>>
>>>> On Jun 21, 2011, at 10:24 AM, Daniel Herzig wrote:
>>>>
>>>>>
>>>>> Hi Martin,
>>>>>
>>>>> Have you tried to put a Squid [1]  as reverse proxy in front of your servers and use delay pools [2] to catch hungry crawlers?
>>>>>
>>>>> Cheers,
>>>>> Daniel
>>>>>
>>>>> [1] http://www.squid-cache.org/
>>>>> [2] http://wiki.squid-cache.org/Features/DelayPools
>>>>>
>>>>> On 21.06.2011, at 09:49, Martin Hepp wrote:
>>>>>
>>>>>> Hi all:
>>>>>>
>>>>>> For the third time in a few weeks, we had massive complaints from site-owners that Semantic Web crawlers from Universities visited their sites in a way close to a denial-of-service attack, i.e., crawling data with maximum bandwidth in a parallelized approach.
>>>>>>
>>>>>> It's clear that a single, stupidly written crawler script, run from a powerful University network, can quickly create terrible traffic load. 
>>>>>>
>>>>>> Many of the scripts we saw
>>>>>>
>>>>>> - ignored robots.txt,
>>>>>> - ignored clear crawling speed limitations in robots.txt,
>>>>>> - did not identify themselves properly in the HTTP request header or lacked contact information therein, 
>>>>>> - used no mechanisms at all for limiting the default crawling speed and re-crawling delays.
>>>>>>
>>>>>> This irresponsible behavior can be the final reason for site-owners to say farewell to academic/W3C-sponsored semantic technology.
>>>>>>
>>>>>> So please, please - advise all of your colleagues and students to NOT write simple crawler scripts for the billion triples challenge or whatsoever without familiarizing themselves with the state of the art in "friendly crawling".
>>>>>>
>>>>>> Best wishes
>>>>>>
>>>>>> Martin Hepp
>>>>>>
>>>>>
>>>>
>>>>
>>>
>>
> 


Received on Wednesday, 22 June 2011 14:04:33 UTC

This archive was generated by hypermail 2.4.0 : Thursday, 24 March 2022 20:29:54 UTC