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salam every one, this is a topic from google web master centrale blog:
Web publishers often ask us how they can maximize their visibility on the web. Much of this has to do with search engine optimization -- making sure a publisher's content shows up on all the search engines. However, there are some cases in which publishers need to communicate more information to search engines -- like the fact that they don't want certain content to appear in search results. And for that they use something called the Robots Exclusion Protocol (REP), which lets publishers control how search engines access their site: whether it's controlling the visibility of their content across their site (via robots.txt) or down to a much more granular level for individual pages (via META tags). Since it was introduced in the early '90s, REP has become the de facto standard by which web publishers specify which parts of their site they want public and which parts they want to keep private. Today, millions of publishers use REP as an easy and efficient way to communicate with search engines. Its strength lies in its flexibility to evolve in parallel with the web, its universal implementation across major search engines and all major robots, and in the way it works for any publisher, no matter how large or small. While REP is observed by virtually all search engines, we've never come together to detail how we each interpret different tags. Over the last couple of years, we have worked with Microsoft and Yahoo! to bring forward standards such as Sitemaps and offer additional tools for webmasters. Since the original announcement, we have, and will continue to, deliver further improvements based on what we are hearing from the community. Today, in that same spirit of making the lives of webmasters simpler, we're releasing detailed documentation about how we implement REP. This will provide a common implementation for webmasters and make it easier for any publisher to know how their REP directives will be handled by three major search providers -- making REP more intuitive and friendly to even more publishers on the web. So, without further ado... Common REP Directives The following list are all the major REP features currently implemented by Google, Microsoft, and Yahoo!. With each feature, you'll see what it does and how you should communicate it. Each of these directives can be specified to be applicable for all crawlers or for specific crawlers by targeting them to specific user-agents, which is how any crawler identifies itself. Apart from the identification by user-agent, each of our crawlers also supports Reverse DNS based authentication to allow you to verify the identity of the crawler. 1. Robots.txt Directives
2. HTML META Directives
These directives are applicable for all forms of content. They can be placed in either the HTML of a page or in the HTTP header for non-HTML content, e.g., PDF, video, etc. using an X-Robots-Tag. You can read more about it here:X-Robots-Tag Post or in our series of posts about using robots and Meta Tags. Other REP Directives The directives listed above are used by Microsoft, Google and Yahoo!, but may not be implemented by all other search engines. In addition, the following directives are supported by Google, but are not supported by all three as are those above: UNAVAILABLE_AFTER Meta Tag - Tells a crawler when a page should "expire", i.e., after which date it should not show up in search results. NOIMAGEINDEX Meta Tag - Tells a crawler not to index images for a given page in search results. NOTRANSLATE Meta Tag - Tells a crawler not to translate the content on a page into different languages for search results. Going forward, we plan to continue to work together to ensure that as new uses of REP arise, we're able to make it as easy as possible for webmasters to use them. So stay tuned for more! Learn more You can find out more about robots.txt in our documentation and at Google's Webmaster help center, which contains lots of helpful information, including:
To see what our colleagues have to say, you can also check out the blog posts published by Yahoo! and Microsoft.this is a topic published in 2013... to get contents for your blog or your forum, just contact me at: devnasser@gmail.com |
Labels: crawling and indexing
