> Common Crawl will use blekko’s metadata to improve its crawl quality, while avoiding webspam, porn, and the influence of excessive SEO (search engine optimization)
Why avoid porn? Millions of people deliberately search for porn on the internet every day. It's hardly less worthy of crawling than any other content. The next sentence goes on to suggest that porn is not "useful to humans", which is obviously false.
If Common Crawl is indeed filtering out content they determine to be pornographic, I hope they are taking care not to also remove information on sexual and relationship health and LGBT rights, which are often collateral damage of porn-blocking systems. And it would be nice to see an open acknowledgement that filtering is going on - I couldn't find any references to this at commoncrawl.org.
We do not have anything against porn. However, when people are not searching for porn, showing them porn results makes for a bad search experience. So identifying porn, and only showing porn on relevant porn results is vitally important to search quality.
Your answer is a bit at odds with http://news.ycombinator.com/item?id=4933437
One of the funny things about language is that there is always a 'pun' or an innuendo which can trigger a hit on a porn site, however if most of what you're looking for isn't porn then the web site has to assume you are not looking for porn and avoid some NSFW link from surfacing into your search results. You could always explicitly ask for it with /porn but then that is a clear signal of what you are looking for.
Part of the crawl data includes an indication as to whether or not the ranker thought the document was 'porn' or 'not porn', so if you're selecting things to return you can ignore that bit, mixing porn with non-porn when someone searches for 'beavers' you get a wider variety of results than you would if you were assuming you meant the furry critters which chew on trees or sports teams and limiting results to those documents.
Having it there but tagged is halfway towards being able to use it to filter them out. Not having it means that when you merge it with another set that you're not going to be able to remove the porn.
And it also allows you to use it as a training set for classifiers.
One could imagine a project on Common Crawl which auto-generated a list of slang terms for porny things by creating a list of n-grams from the words used in documents tagged as porn.
I really appreciate your mention of LGBT and sexual health sites being collateral damage - we need to draw more attention to that problem. I would love to see someone work with Common Crawl to improve methods of distinguishing.
> The next sentence goes on to suggest that porn is not
> "useful to humans", which is obviously false.