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Using Web Crawler
What is web crawler?
Also known as a Web spider or Web robot.
Other less frequently used names for Web crawlers are ants, automatic indexers, bots, and worms.
“ A program or automated script which browses the World Wide Web in a methodical, automated manner”
(Kobayashi and Takeda, 2000).
What is web crawler?
The process or program used by search engines to download pages from the web for later processing by a search engine that will index the downloaded pages to provide fast searches.
How does web crawler work?
It starts with a list of URLs to visit, called the seeds. As the crawler visits these URLs, it identifies all the hyperlinks in the page and adds them to the list of visited URLs, called the crawl frontier.
URLs from the frontier are recursively visited according to a set of policies.
How does web crawler work?
Algorithms that we are using for extracting text
KNUTT-MORRIS-PRATT (KMP)
FINITE AUTOMATA
BOYER MOORE (BMM)
KNUTT-MORRIS-PRATT (KMP)
works much like finite automata algorithm. Pattern and text are compared in a left to right scan
The data we need to find the next shifting position is stored in an auxiliary “next” table which is computed in a pre- processing step by comparing the pattern with itself
BOYER MOORE (BMM)
The pattern is scanned from right to left when proceeding though the text.
BM works with two different pre-processing strategies to determine the smallest possible shift, each time a mismatch occursalgorithm computes both and then chooses the largest possible shift
FINITE AUTOMATA
uses a finite automaton to scan for occurrence of the pattern in the text.
A finite automaton is a 5-tuple(S,s0,A, ,d), where
- S is a finite set of states
- s0 is the start state
- A S is a distinguished set of accepting states
- * is a finite input alphabet
- D is a function from S × * into S, called the transition function of the automaton.
Implementation
We presented the working and design of web crawler. Here, the working of kmp, finite and boyer moore algorithm is also shown.
Here, to run the crawler we will give one seed url, keyword and the path for text file as input.
When we press the search button it will take the urls that match the keyword from internet.
Runing search engine
DATA DOWNLOAD
FILE DIRECTORY
FILE OPEN

Web Crawler

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INTRODUCTION


Definition:A Web crawler is a computer program that browses the World Wide Web in a methodical, automated manner.
The Role of crawlers is to collect web content


Types of crawler

Batch crawler : its sanpsnot of their crawl space,unlit reaching a certain size or time limit,certain number of pages are crawled
Incremental crawler : continuously crawl their crawl space,revisiting URLs to ensure freshness
Focused crawler : attempt to crawl pages pertaining to some topic,while minimizing number of off-topic pages that are collected


Features of a crawler


-Robustness: spider traps

-Infinitely deep directory structures
-Pages filled a large number of characters


conclusions

All the serch engines/companies employ research staff which are also academically involved: sit on PCs referee journal papers,present at conferences