Web Crawler: How Spiders Help Website Work Better

1
(No Transcript)
2
It is harder for a search bot to determine
whether all information has been properly indexed
on the Internet, as opposed to a library, which
has physical piles of books. If the web crawler
bot wishes to collect all the relevant
information that the Internet has to offer, it
begins by scanning a certain set of known
webpages and then follow hyperlinks from those
pages to other pages, follow hyperlinks from
those other pages to additional pages, and so
on. Search engine bots do not crawl all of the
websites that are publicly accessible. The
Internet contains billions of web pages but
only 40-70 can be searched.
3
The purpose of search indexing
By establishing search indexing, a search engine
can learn where on the Internet to find
information when a user searches for it. It is
similar to organizing a library card catalog for
the Internet. An annotated bibliography may also
be analogous to it, as it lists all references to
a particular topic or phrase in the book. Search
engines use indexing primarily to locate content
within pages and to identify data about the
pages that are not visible to users. In most
cases, when a search engine indexes a page, it
includes every word except for articles like A,
An and The in Googles case. Search engines use
an index of all pages that appear with those
terms to select the most relevant ones when users
use those words. A webpages metadata describes
what it contains to search engines as part of the
indexing process. Often, what appears on search
engine result pages are the meta title and meta
description, rather than the visible content on a
webpage.
4
How do web crawlers work?
Change and expansion are constants on the
Internet. The seed, or list of known URLs, is
used by web crawlers because it is impossible to
know the total number of web pages on the
Internet. Crawling starts with these URLs. The
crawlers find hyperlinks to various URLs as they
crawl those webpages, and they include those URLs
in their list of pages to crawl next. Considering
how many pages there are available on the
internet for search, it would take a very long
time to complete. Web crawlers, on the other
hand, are programmed to follow certain policies
that make it more selective about which pages to
crawl, the order they should crawl them in, and
how often they should crawl them to ensure they
have not updated their content. There is no
general method for finding the relative
importance of every webpage instead, web
crawlers choose which webpages to crawl first
based on how many other pages link to that page,
how many visitors the page receives, and other
factors indicating the likelihood the page
includes valuable information.
5
Its important that a search engine indexes a
webpage that gets a lot of traffic and is cited
by a lot of other web pages, just as a library
ensures that a popular book is available for
checkout frequently. Reviewing web pages Web
content constantly changes, disappears, or moves.
Crawlers will periodically have to visit pages in
order to index the most current versions of
content. The robots.txt protocol also dictates
which pages to crawl The process of crawling
each page is determined by a robots.txt file.
Prior to crawling a page, the search engine
spiders check the robots.txt file on the web
server that controls that page. Robots.txt files
are used to specify what rules bots should follow
if they access a website hosted on the server or
even an application. Bots can follow these links
and crawl these pages if they comply with these
rules. Each search engine makes their spider
bots weigh these factors differently based on its
own proprietary algorithm. Although the goal of
search engine web crawlers is to download and
index content from web pages, they act
differently depending on which search engine they
are running.
6
What is the meaning of the word "spider" in web
crawling
The access of web crawler bots to web properties
should always be allowed?
In fact, the www part of most website URLs
refers to parts of the World Wide Web, or at
least what most users access. As spiders crawl on
spiderwebs, so too have search engine bots
crawled worldwide on the Web.
That depends on a number of factors, and is up to
the web property. The server must respond to
requests made by web crawlers in order to index
content just as a user or another bot accessing
a website would. The website operator may find
it beneficial not to allow search indexing too
often, depending on how much content is on each
page, how many pages exist, or other factors. An
excessive amount of indexing can overburden the
server or drive up bandwidth costs.
7
Also, some organizations and developers may not
want certain webpages to be accessible to users
unless they have been given access to the page
beforehand, here access means a link to the web
page. Creating a landing page for a marketing
campaign is an example of a case where
enterprises do not want unauthorized individuals
to access it. They can use this information to
tailor messages or precisely measure a pages
performance. Businesses can use no-index or a
tag to block search engines from displaying
their landing pages. The disallow tag or
robots.txt file will prevent search engine
spiders from crawling the page. Numerous reasons
exist for not wanting to have a website indexed
by search engines. The search results pages on a
website that allows users to search within its
domain may be blocked since users are not
interested in them. Additionally, there should
also be a way to block automatically created
pages that are only meant for a few specific
users.
8
Web crawling vs. web scraping which is better?
Web scraping, data scraping, or content scraping
refers to the act of downloading content on a
website without the webmasters consent, usually
in order to use it maliciously. Scraping of web
pages is typically more targeted than web
crawling. Website scrapers are focused on
particular pages or websites, but web crawlers
will keep crawling those pages forever. Also,
scrapers may ignore the burden placed on servers,
while web crawlers, most notably search engine
crawlers, observe the robots.txt file and make
fewer requests to avoid overloading the server.
9
Does Web Crawling Affect SEO?
A websites search engine ranking can be improved
by search engine optimization, which prepares the
content for search engine indexing. Search
engines do not index a website if spider bots
havent crawled it. It is therefore very
important that a website owner does not block web
crawler bots if they want organic traffic from
search results.
10
Which web crawler spiders are currently operating
on the Internet?

• The bots from the major search engines are
  called
• Google Googlebot
• Yandex (Russian search engine) Yandex Bot
• Bing Bingbot
• Baidu (Chinese search engine) Baidu Spider
• Aside from web crawler bots associated with
  search engines, there are several less common
  bots that crawl the Internet.
• Finally, Web crawlers play an important role in
  understanding a website and its contents. Web
  spiders are an important aspect of search engines
  and how they communicate with our content.

11
(No Transcript)