Search Engine Robots or web Crawlers
Most of the popular consumers or website traffic hire option offered search engines towards search out the piece of articles they essential. However how this material is delivered by search engines? Exactly where towards they comprise gathered these types of information? In essence most of such search engines continue to keep their particular database of content material. Those people databases consists of the internet websites out there within just the webworld which inevitably hold the matter world-wide-web webpages written content for each available internet sites. Simply just search engine do some background effort and hard work by means of utilizing robots in direction of gather articles and preserve the database. They generate catalog of accumulated material and then clearly show it publicly or at-times for personal employ the service of.
Inside of this article we will talk about regarding people entities which loiter in just the worldwide net entire world or we will about world-wide-web crawlers which transfer in the vicinity of inside netspace. We will understand
· What it’s all around and what reason they serve ?
· Pros and shortcomings of using such entities.
· How we can hold our pages absent towards crawlers ?
· Differences in between the popular crawlers and robots.
In the following portion we will divide the whole research work under the following two sections :
I. Search Engine Spider : Robots.txt.
II. Search Engine Robots : Meta-tags Explained.
I. Search Engine Spider : Robots.txt
What is robots.txt file ?
A web robot is a program or search engine software that visits sites regularly and automatically and crawl through the web’s hypertext structure by fetching a document, and recursively retrieving all the documents which are referenced. Sometimes site owners do not want all their site pages to be crawled by the web robots. For this reason they can exclude few of their pages being crawled by the robots by using some standard agents. So most of the robots abide by the ‘Robots Exclusion Standard’, a set of constraints to restricts robots behavior.
‘Robot Exclusion Standard’ is a protocol used by the site administrator to control the movement of the robots. When search engine robots come to a site it will search for a file named robots.txt in the root
domain of the site (
http://www.anydomain.com/robots.txt). This is a plain text file which implements ‘Robots Exclusion Protocols’ by allowing or disallowing specific files within the directories of files. Site administrator can disallow access to cgi, temporary or private directories by specifying robot user agent names.
The format of the robot.txt file is very simple. It consists of two field : user-agent and one or more disallow field.
What is User-agent ?
This is the technical name for an programming concepts in the world wide networking environment and used to mention the specific search engine robot within the robots.txt file.
For example :
User-agent: googlebot
We can also use the wildcard character “*” to specify all robots :
User-agent: *
Means all the robots are allowed to come to visit.
What is Disallow ?
In the robot.txt file second field is known as the disallow: These lines guide the robots, to which file should be crawled or which should not be. For example to prevent downloading email.htm the syntax will be:
Disallow: email.htm
Prevent crawling through directories the syntax will be:
Disallow: /cgi-bin/
White Space and Comments :
Using # at the beginning of any line in the robots.txt file will be considered as comments only and using # at the beginning of the robots.txt like the following example entail us which url to be crawled.
# robots.txt for
www.anydomain.comEntry Details for robots.txt :
1) User-agent: *
Disallow:
The asterisk (*) in the User-agent field is denoting “all robots” are invited. As nothing is disallowed so all robots are free to crawl through.
2) User-agent: *
Disallow: /cgi-bin/
Disallow: /temp/
Disallow: /private/
All robots are allowed to crawl through the all files except the cgi-bin, temp and private file.
3) User-agent: dangerbot
Disallow: /
Dangerbot is not allowed to crawl through any of the directories. “/” stands for all directories.
4) User-agent: dangerbot
Disallow: /
User-agent: *
Disallow: /temp/
The blank line indicates starting of new User-agent records. Except dangerbot all the other bots are allowed to crawl through all the directories except “temp” directories.
5) User-agent: dangerbot
Disallow: /links/listing.html
User-agent: *
Disallow: /email.html/
Dangerbot is not allowed for the listing page of links directory otherwise all the robots are allowed for all directories except downloading email.html page.
6) User-agent: abcbot
Disallow: /*.gif$
To remove all files from a specific file type (e.g. .gif ) we will use the above robots.txt entry.
7) User-agent: abcbot
Disallow: /*?
To restrict web crawler from crawling dynamic pages we will use the above robots.txt entry.
Note : Disallow field may contain “*” to follow any series of characters and may end with “$” to indicate the end of the name.
Eg : Within the image files to exclude all gif files but allowing others from google crawling
User-agent: Googlebot-Image
Disallow: /*.gif$
Disadvantages of robots.txt :
Problem with Disallow field:
Disallow: /css/ /cgi-bin/ /images/
Different spider will read the above field in different way. Some will ignore the spaces and will read /css//cgi-bin//images/ and may only consider either /images/ or /css/ ignoring the others.
The correct syntax should be :
Disallow: /css/
Disallow: /cgi-bin/
Disallow: /images/
All Files listing:
Specifying each and every file name within a directory is most commonly used mistake
Disallow: /ab/cdef.html
Disallow: /ab/ghij.html
Disallow: /ab/klmn.html
Disallow: /op/qrst.html
Disallow: /op/uvwx.html
Above portion can be written as:
Disallow: /ab/
Disallow: /op/
A trailing slash means a lot that is a directory is offlimits.
Capitalization:
USER-AGENT: REDBOT
DISALLOW:
Though fields are not case sensitive but the datas like directories, filenames are case sensitive.
Conflicting syntax:
User-agent: *
Disallow: /
#
User-agent: Redbot
Disallow:
What will happen ? Redbot is allowed to crawl everything but will this permission override the disallow field or disallow will override the allow permission.
II. Search Engine Robots: Meta-tag Explained:
What is robot meta tag ?
Besides robots.txt search engine is also having another tools to crawl through web pages. This is the META tag which tells web spider to index a page and follow links on it, which may be more helpful in some cases, as it can be used on page-by-page basis. It is also helpful incase you don’t have the requisite permission to access the servers root directory to control robots.txt file.
We used to place this tag within the header portion of html.
Format of the Robots Meta tag :
In the HTML document it is placed in the HEAD section.
html
head
META NAME=”robots” CONTENT=”index,follow”
META NAME=”description” CONTENT=”Welcome to…….”
title……………title
head
body
Robots Meta Tag options :
There are four options that can be used in the CONTENT portion of the Meta Robots. These are index, noindex, follow, nofollow.
This tag allowing search engine robots to index a specific page and can follow all the link residing on it. If site admin doesn’t want any pages to be indexed or any link to be followed then they can replace “ index,follow” with “ noindex,nofollow”.
According to the requirements, site admin can use the robots in the following different options :
META NAME=”robots” CONTENT=”index,follow”> Index this page, follow links from this page.
META NAME=”robots” CONTENT =”noindex,follow”> Don’t index this page but follow link from this page.
META NAME=”robots” CONTENT =”index,nofollow”> Index this page but don’t follow links from this page
META NAME=”robots” CONTENT =”noindex,nofollow”> Don’t index this page, don’t follow links from this page.
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